ohhhhhhhh right backslashes on windows, shit

w00t

Cargo.toml

@@ -10,11 +10,12 @@ thiserror = "1.0"
 macros = { path = "macros" }
 dirs = "4"
 
-log = "0.4"
+log = { version = "0.4", features = [ "max_level_debug", "release_max_level_off" ] }
 
 [dependencies.windows]
 version = "0.44.0"
 features = [
     "Win32_Foundation",
     "Win32_System_Console",
+    "Win32_UI_Input_KeyboardAndMouse"
 ]

README.md

@@ -0,0 +1,44 @@
+# clyde
+
+A command-line shell for Windows.
+
+## examples
+
+In all examples, the Clyde prompt is written as follows:
+
+```
+▷
+```
+
+### Run a built-in command
+
+Built-in commands are invoked by executing them with a bare string
+
+```
+c:\dev\clyde ▷ cd src
+c:\dev\clyde\src ▷
+```
+
+### Run an external command
+
+External commands are invoked in the same way:
+
+```
+c:\dev\clyde ▷ git status
+On branch main
+Your branch is up to date with 'origin/main'.
+
+nothing to commit, working tree clean
+```
+
+### Run commands back to back
+
+To run two commands back to back, separate them with a semicolon. Note that
+this interaction is entirely unconditional: the second command executes
+regardless of whether the first command succeeded or not.
+
+```
+c:\dev\clyde ▷ echo one; echo two
+one
+two
+```

src/builtin.rs

@@ -0,0 +1,82 @@
+/// changes directory
+mod cd;
+
+mod ls;
+
+/// prints stuff
+mod echo;
+
+/// prints environment variables
+mod printenv;
+
+mod pwd;
+
+/// removes files
+mod rm;
+
+mod mkdir;
+
+/// the butt of a file
+mod tail;
+
+/// locates a binary on our PATH
+mod which;
+
+use crate::{
+    error::ExecError,
+    run::{Call, Context, Value},
+};
+use std::collections::HashMap;
+
+/// All of the builtin commands that exist
+#[derive(Clone, Copy)]
+pub enum Builtin {
+    Changedir,
+    Echo,
+    Ls,
+    Mkdir,
+    Printenv,
+    Pwd,
+    Rm,
+    Tail,
+    Which,
+}
+
+impl Builtin {
+    fn resolve(&self) -> &dyn Call {
+        use Builtin::*;
+        match self {
+            Changedir => &cd::Changedir,
+            Echo => &echo::Echo,
+            Ls => &ls::Ls,
+            Mkdir => &mkdir::Mkdir,
+            Printenv => &printenv::Printenv,
+            Pwd => &pwd::Pwd,
+            Rm => &rm::Rm,
+            Tail => &tail::Tail,
+            Which => &which::Which,
+        }
+    }
+}
+
+impl Call for Builtin {
+    fn call(&self, ctx: &mut Context, args: &[Value]) -> Result<Value, ExecError> {
+        self.resolve().call(ctx, args)
+    }
+}
+
+/// A mapping of all of the builtin command values to their names
+pub fn all() -> HashMap<&'static str, Builtin> {
+    use Builtin::*;
+    HashMap::from([
+        ("cd", Changedir),
+        ("echo", Echo),
+        ("ls", Ls),
+        ("mkdir", Mkdir),
+        ("printenv", Printenv),
+        ("pwd", Pwd),
+        ("rm", Rm),
+        ("tail", Tail),
+        ("which", Which),
+    ])
+}

src/builtin/cd.rs

@@ -0,0 +1,25 @@
+use crate::{
+    error::ExecError,
+    run::{Call, Context, Value},
+};
+use std::env;
+
+pub struct Changedir;
+
+impl Call for Changedir {
+    fn call(&self, _ctx: &mut Context, args: &[Value]) -> Result<Value, ExecError> {
+        match args.len() {
+            0 => {
+                todo!()
+            }
+            1 => {
+                let name = args[0].try_as_str()?;
+                env::set_current_dir(name).map_err(|e| ExecError::Misc(e.to_string()))?;
+            }
+            _ => {
+                todo!()
+            }
+        }
+        Ok(Value::None)
+    }
+}

src/builtin/echo.rs

@@ -0,0 +1,18 @@
+use crate::{
+    error::ExecError,
+    run::{Call, Context, Value},
+};
+use std::io::Write;
+
+pub struct Echo;
+
+impl Call for Echo {
+    fn call(&self, ctx: &mut Context, args: &[Value]) -> Result<Value, ExecError> {
+        let args = args
+            .into_iter()
+            .map(|v| v.try_as_str())
+            .collect::<Result<Vec<_>, _>>()?;
+        _ = write!(ctx.stdout, "{}\n", args.join(" "));
+        Ok(Value::None)
+    }
+}

src/builtin/ls.rs

@@ -0,0 +1,24 @@
+use crate::{
+    error::ExecError,
+    run::{Call, Context, Value},
+};
+use std::{env, fs, io::Write};
+
+pub struct Ls;
+
+impl Call for Ls {
+    fn call(&self, ctx: &mut Context, _args: &[Value]) -> Result<Value, ExecError> {
+        let cwd = env::current_dir()?;
+        let dir = fs::read_dir(&cwd)?;
+        for child in dir {
+            let child_path = child?.path();
+            let fname = child_path
+                .file_name()
+                .ok_or_else(|| ExecError::new("no file name"))?
+                .to_str()
+                .ok_or_else(|| ExecError::new("non-unicode file name"))?;
+            _ = write!(ctx.stdout, "{}\n", fname);
+        }
+        Ok(Value::None)
+    }
+}

src/builtin/mkdir.rs

@@ -0,0 +1,25 @@
+use crate::{
+    error::ExecError,
+    run::{Call, Context, Value},
+};
+use std::fs;
+
+pub struct Mkdir;
+
+impl Call for Mkdir {
+    fn call(&self, _ctx: &mut Context, args: &[Value]) -> Result<Value, ExecError> {
+        match args.len() {
+            0 => {
+                todo!()
+            }
+            1 => {
+                let path = args[0].try_as_str()?;
+                fs::create_dir(path)?;
+            }
+            _ => {
+                todo!()
+            }
+        }
+        Ok(Value::None)
+    }
+}

src/builtin/printenv.rs

@@ -0,0 +1,26 @@
+use crate::{
+    error::ExecError,
+    run::{Call, Context, Value},
+};
+use std::{env, io::Write};
+
+pub struct Printenv;
+
+impl Call for Printenv {
+    fn call(&self, ctx: &mut Context, args: &[Value]) -> Result<Value, ExecError> {
+        if args.len() > 0 {
+            for arg in args {
+                let name = arg.try_as_str()?;
+                _ = match env::var(name) {
+                    Ok(val) => writeln!(ctx.stdout, "{}", val),
+                    Err(e) => writeln!(ctx.stderr, "ERROR {}", e),
+                };
+            }
+        } else {
+            for (name, val) in env::vars() {
+                _ = writeln!(ctx.stdout, "{name}={val}");
+            }
+        }
+        Ok(Value::None)
+    }
+}

src/builtin/pwd.rs

@@ -0,0 +1,15 @@
+use crate::{
+    error::ExecError,
+    run::{Call, Context, Value},
+};
+use std::{env, io::Write};
+
+pub struct Pwd;
+
+impl Call for Pwd {
+    fn call(&self, ctx: &mut Context, args: &[Value]) -> Result<Value, ExecError> {
+        let cwd = env::current_dir()?;
+        _ = write!(ctx.stdout, "{}\n", cwd.display());
+        Ok(Value::None)
+    }
+}

src/builtin/rm.rs

@@ -0,0 +1,25 @@
+use crate::{
+    error::ExecError,
+    run::{Call, Context, Value},
+};
+use std::fs;
+
+pub struct Rm;
+
+impl Call for Rm {
+    fn call(&self, _ctx: &mut Context, args: &[Value]) -> Result<Value, ExecError> {
+        match args.len() {
+            0 => {
+                todo!()
+            }
+            1 => {
+                let path = args[0].try_as_str()?;
+                fs::remove_file(path).map_err(|err| ExecError::Misc(err.to_string()))?;
+            }
+            _ => {
+                todo!()
+            }
+        }
+        Ok(Value::None)
+    }
+}

src/builtin/tail.rs

@@ -1,30 +1,18 @@
 use crate::{
-    ext::Command,
-    output,
+    error::ExecError,
+    run::{Call, Context, Value},
 };
-
 use std::{
     fs::File,
-    io::{Seek, SeekFrom, Read, Write},
+    io::{Read, Seek, SeekFrom, Write},
 };
 
-use anyhow::Result;
-
-pub struct Tail { }
-
-impl Command for Tail {
-    fn name() -> String {
-        String::from("tail")
-    }
-
-    fn create() -> Self {
-        Self{ }
-    }
+pub struct Tail;
 
-    fn exec(&mut self, args: Vec<&str>) -> Result<bool> {
-        let mut stdout = output::Writer::stdout()?;
+impl Call for Tail {
+    fn call(&self, ctx: &mut Context, args: &[Value]) -> Result<Value, ExecError> {
         if args.len() > 0 {
-            let fname = args[0];
+            let fname = args[0].try_as_str()?;
             match File::options().read(true).open(fname) {
                 Ok(mut f) => {
                     _ = f.seek(SeekFrom::End(0));
@@ -36,7 +24,7 @@ impl Command for Tail {
                                 if n == 1 {
                                     buf.push(one_byte[0]);
                                     if let Ok(s) = std::str::from_utf8(&buf) {
-                                        stdout.write(s.as_bytes())?;
+                                        _ = ctx.stdout.write(s.as_bytes());
                                         buf.clear();
                                     }
                                 }
@@ -46,13 +34,10 @@ impl Command for Tail {
                     }
                 }
                 Err(e) => {
-                    println!("failed to open file: {}", e);
-                    return Err(e.into());
+                    _ = write!(ctx.stderr, "failed to open file: {}", e);
                 }
             }
-        } else {
-            println!("need a file name");
-            return Ok(false);
         }
+        Ok(Value::None)
     }
 }

src/builtin/which.rs

@@ -0,0 +1,26 @@
+use crate::{
+    error::ExecError,
+    run::{Call, Context, Value},
+};
+use std::{env, io::Write};
+
+pub struct Which;
+
+impl Call for Which {
+    fn call(&self, ctx: &mut Context, args: &[Value]) -> Result<Value, ExecError> {
+        let path = env::var("path").unwrap_or_default();
+        let dirs: Vec<&str> = path.split(";").collect();
+
+        for arg in args {
+            let name = arg.try_as_str()?;
+            for d in dirs.iter() {
+                let dir = std::path::Path::new(d);
+                let fname = dir.join(name).with_extension("exe");
+                if fname.exists() && fname.is_file() {
+                    _ = writeln!(ctx.stdout, "{}", fname.to_str().unwrap());
+                }
+            }
+        }
+        Ok(Value::None)
+    }
+}

src/edit.rs

@@ -0,0 +1,474 @@
+use crate::{
+    history::History,
+    input::{self, ControlCharacter, Escape},
+    log::*,
+    output,
+    prompt::Prompt,
+};
+
+use anyhow::Result;
+use std::{cmp::min, io::Write};
+
+/// The text buffer of a text editor.
+pub struct Buffer {
+    /// the current text of the edit buffer
+    chars: Vec<char>,
+
+    /// the position of our edit cursor within [Self::chars]
+    cursor: usize,
+}
+
+impl Buffer {
+    /// an empty buffer
+    pub fn new() -> Self {
+        Self {
+            chars: Vec::new(),
+            cursor: 0,
+        }
+    }
+
+    /// clears our edit buffer
+    pub fn clear(&mut self) {
+        self.cursor = 0;
+        self.chars.clear();
+        self.show_debug();
+    }
+
+    /// takes the text out of the editor, leaving an empty buffer in its place
+    fn pop(&mut self) -> String {
+        let s: String = self.chars.iter().collect();
+        self.clear();
+        self.show_debug();
+        s
+    }
+
+    fn show(&self) -> String {
+        self.chars.iter().collect()
+    }
+
+    /// moves the edit cursor back by a fixed number of characters without modifying the contents
+    /// of the buffer
+    fn back(&mut self, n: usize) -> bool {
+        if self.cursor > 0 {
+            if n > self.cursor {
+                self.cursor = n;
+            } else {
+                self.cursor -= n;
+            }
+            self.show_debug();
+            true
+        } else {
+            false
+        }
+    }
+
+    /// drops a character from the text buffer at the cursor's location
+    fn backspace(&mut self) -> bool {
+        if self.chars.len() > 0 {
+            if self.cursor > 0 {
+                self.cursor -= 1;
+            }
+            self.chars.remove(self.cursor);
+            self.show_debug();
+            true
+        } else {
+            false
+        }
+    }
+
+    /// removes the elements left of the cursor, returning the count of removed elements
+    fn clear_left(&mut self) -> usize {
+        if self.cursor > 0 {
+            let n = self.chars.drain(..self.cursor).count();
+            self.cursor = 0;
+            self.show_debug();
+            n
+        } else {
+            0
+        }
+    }
+
+    /// moves the edit cursor to the beginning of the buffer. The returned value is the index of
+    /// the edit cursor before the move.
+    fn seek_left(&mut self) -> usize {
+        let n = self.cursor;
+        self.cursor = 0;
+        self.show_debug();
+        n
+    }
+
+    /// moves the edit cursor to the end of the buffer. The returned value is the index of th eedit
+    /// cursor before the move.
+    fn seek_right(&mut self) -> usize {
+        let n = self.chars.len() - self.cursor;
+        self.cursor = self.chars.len();
+        self.show_debug();
+        n
+    }
+
+    /// moves the edit cursor forward by n positions
+    fn forward(&mut self, n: usize) -> bool {
+        if self.cursor < self.chars.len() {
+            self.cursor = min(self.chars.len(), self.cursor + n);
+            self.show_debug();
+            true
+        } else {
+            false
+        }
+    }
+
+    /// inserts a character into the edit buffer at the cursor's current location
+    fn insert(&mut self, c: char) {
+        self.chars.insert(self.cursor, c);
+        self.cursor += 1;
+        self.show_debug();
+    }
+
+    /// the portion of the text buffer from the edit cursor to the end of the buffer
+    fn tail(&self) -> String {
+        let mut start = self.cursor;
+        if start > 0 {
+            start -= 1;
+        }
+
+        let chars = &self.chars[start..];
+        chars.iter().collect()
+    }
+
+    /// the current position of the edit cursor
+    fn pos(&self) -> usize {
+        self.cursor
+    }
+
+    /// the length of the text buffer
+    fn len(&self) -> usize {
+        self.chars.len()
+    }
+
+    fn show_debug(&self) {
+        let before = if self.chars.len() > 0 {
+            self.chars[0..self.cursor].to_vec().iter().collect()
+        } else {
+            String::new()
+        };
+
+        let after = if self.chars.len() > 0 {
+            self.chars[self.cursor..].to_vec().iter().collect()
+        } else {
+            String::new()
+        };
+
+        debug!(
+            "  {: <5} {: >5} {}·{}",
+            self.cursor,
+            self.chars.len(),
+            before,
+            after
+        );
+    }
+}
+
+/// Describes how we handle an action from the editor
+enum Status {
+    /// Editing is still in progress
+    Ongoing,
+
+    /// A command has been entered in the editor and should be sent to the interpreter
+    Submit(String),
+
+    /// The edit session has ended and the shell should shut down
+    Done,
+}
+
+/// A primitive terminal-based text editor
+pub struct Editor {
+    /// the incoming terminal events
+    input: input::Reader,
+
+    /// the in-memory representation of the command that we're currently editing
+    buffer: Buffer,
+
+    /// our outgoing terminal events, which is used as the display portion of the editor
+    display: output::Writer,
+
+    /// this thing draws our prompt
+    prompt: Prompt,
+
+    /// Our current position when scrolling through the history. A hist_pos of 0 means that we're
+    /// not looking at the history. hist_pos of 1 means that we're looking at the first most-recent
+    /// command entered.
+    hist_pos: usize,
+}
+
+impl Editor {
+    pub fn new() -> Result<Self> {
+        Ok(Self {
+            input: input::Reader::new()?,
+            buffer: Buffer::new(),
+            display: output::Writer::stdout()?,
+            prompt: Prompt::new(),
+            hist_pos: 0,
+        })
+    }
+
+    /// reads one command from the editor. This function blocks until the user has entered an
+    /// entire command.
+    pub fn read_command(&mut self, history: &mut History) -> Result<Option<String>> {
+        use input::Event::*;
+
+        loop {
+            let event = self.input.next()?;
+            let status = match event {
+                Key(e) => self.handle_key_press(e)?,
+                Focus(true) => {
+                    self.focus_start();
+                    Status::Ongoing
+                }
+                Focus(false) => {
+                    self.focus_end();
+                    Status::Ongoing
+                }
+                Control(cc) => self.handle_control(cc)?,
+                Escape(escape) => self.handle_escape(escape, history)?,
+                Size => {
+                    debug!("ignoring size event");
+                    Status::Ongoing
+                }
+                Menu(_) => {
+                    debug!("ignoring menu event");
+                    Status::Ongoing
+                }
+                Mouse { x, y } => {
+                    debug!("ignoring mouse event {x}, {y}");
+                    Status::Ongoing
+                }
+            };
+            match status {
+                Status::Ongoing => {}
+                Status::Done => return Ok(None),
+                Status::Submit(e) => {
+                    self.hist_pos = 0;
+                    return Ok(Some(e));
+                }
+            }
+        }
+    }
+
+    fn handle_key_press(&mut self, event: crate::key::Event) -> Result<Status> {
+        use crate::key::codes::*;
+        match event {
+            _ if event.code == ENTER || event.char == '\r' => return self.submit(),
+            _ if event.code == TAB || event.char == '\t' => {}
+            _ if event.char == '\u{7f}' => self.backspace()?,
+            _ if event.ctrl && event.code == A => self.seek_left()?,
+            _ if event.ctrl && event.code == D => return Ok(Status::Done),
+            _ if event.ctrl && event.code == E => self.seek_right()?,
+            _ if event.ctrl && event.code == U => self.clear_left()?,
+            _ if event.down && !event.char.is_control() => self.insert(event.char)?,
+            _ => debug!("ignored key press: {event:?}"),
+        }
+        Ok(Status::Ongoing)
+    }
+
+    fn handle_escape(&mut self, esc: Escape, history: &History) -> Result<Status> {
+        use Escape::*;
+        match esc {
+            Left => self.back(1)?,
+            Right => self.forward(1)?,
+            Up => self.prev_history(history)?,
+            Down => self.next_history(history)?,
+            Home => self.seek_left()?,
+            End => self.seek_right()?,
+            esc => debug!("  Ignored escape: {esc:?}"),
+        }
+        Ok(Status::Ongoing)
+    }
+
+    fn handle_control(&mut self, cc: ControlCharacter) -> Result<Status> {
+        use ControlCharacter::*;
+        match cc {
+            StartOfHeading => self.seek_left()?,
+            EndOfTransmission => return Ok(Status::Done),
+            Enquiry => self.seek_right()?,
+            Formfeed => self.clear_screen()?,
+            Linefeed => self.insert_dot()?,
+            NegativeAcknowledge => self.clear_left()?,
+            cc => debug!("ignored control character: {cc:?}"),
+        }
+        Ok(Status::Ongoing)
+    }
+
+    fn insert_dot(&mut self) -> Result<()> {
+        self.insert('\u{2022}')?;
+        Ok(())
+    }
+
+    fn submit(&mut self) -> Result<Status> {
+        self.display.newline()?;
+        let text = self.buffer.pop();
+        info!("◇ {}", text);
+        Ok(Status::Submit(text))
+    }
+
+    fn focus_start(&mut self) {}
+
+    fn focus_end(&mut self) {}
+
+    /// moves the edit cursor one character to the left
+    pub fn back(&mut self, n: usize) -> Result<()> {
+        debug!("⛬ ←");
+        if self.buffer.back(n) {
+            self.display.back(n)?;
+        }
+        Ok(())
+    }
+
+    /// moves the edit cursor one character to the right
+    pub fn forward(&mut self, n: usize) -> Result<()> {
+        debug!("⛬ →");
+        if self.buffer.forward(n) {
+            self.display.forward(n)?;
+        }
+        Ok(())
+    }
+
+    /// moves the cursor position to the end of the line
+    pub fn seek_right(&mut self) -> Result<()> {
+        info!("»");
+        let n = self.buffer.seek_right();
+        if n > 0 {
+            // move right by the distance seeked
+            self.display.forward(n)?;
+        }
+        Ok(())
+    }
+
+    /// moves the cursor position to the beginning of the line
+    pub fn seek_left(&mut self) -> Result<()> {
+        info!("«");
+        let n = self.buffer.seek_left();
+        if n > 0 {
+            // move left by the distance seeked
+            self.display.back(n)?;
+        }
+        Ok(())
+    }
+
+    /// clears the line from the current cursor position to the beginning of the line
+    pub fn clear_left(&mut self) -> Result<()> {
+        info!("» clear left");
+        let n = self.buffer.clear_left();
+        if n > 0 {
+            // move left by the number of elements removed
+            self.display.back(n)?;
+            // draw the elements remaining, followed by a space for each removed
+            // element
+            let kept = self.buffer.show();
+            let text = format!("{}{:width$}", kept, "", width = n);
+            self.display.write(text.as_bytes())?;
+            self.display.back(n + kept.chars().count())?;
+        }
+        Ok(())
+    }
+
+    /// clears the scrollback buffer, moving the current edit line to the top of the screen, but
+    /// leaving the edit cursor in place
+    pub fn clear_screen(&mut self) -> Result<()> {
+        info!("» clear");
+        self.display.clear()?;
+        self.prompt.print(&mut self.display)?;
+        self.display.write(self.buffer.show().as_bytes())?;
+        self.display.back(self.buffer.len() - self.buffer.pos())?;
+        self.reset()?;
+        Ok(())
+    }
+
+    pub fn show_prompt(&mut self) -> Result<()> {
+        self.reset()?;
+        self.prompt.print(&mut self.display)?;
+        Ok(())
+    }
+
+    /// inserts a character at edit cursor's current position
+    pub fn insert(&mut self, c: char) -> Result<()> {
+        self.buffer.insert(c);
+
+        let tail = self.buffer.tail();
+        let n = tail.chars().count();
+
+        // write everything from the current line cursor out to the output buffer.
+        self.display.write(tail.as_bytes())?;
+        if n > 1 {
+            // if we wrote more than one character, because we weren't at the end, we
+            // need to rewind the terminal cursor to where it was.
+            self.display.back(n - 1)?;
+        }
+        Ok(())
+    }
+
+    pub fn backspace(&mut self) -> Result<()> {
+        if !self.buffer.backspace() {
+            return Ok(());
+        }
+
+        // move cursor back two spaces
+        self.display.back(2)?;
+        let tail = format!("{} ", self.buffer.tail());
+        let n = tail.chars().count();
+        self.display.write(tail.as_bytes())?;
+
+        // after writing out the tail, rewind by the number of characters in
+        // the tail
+        if n > 1 {
+            self.display.back(n - 1)?;
+        } else {
+            // honestly I can't remember how I figured this out
+            self.display.write(b" \x1b[1D")?;
+        }
+        Ok(())
+    }
+
+    pub fn reset(&mut self) -> Result<()> {
+        self.buffer.clear();
+        self.display.reset()?;
+        Ok(())
+    }
+
+    fn prev_history(&mut self, history: &History) -> Result<()> {
+        let text = match history.look_back(self.hist_pos + 1) {
+            Some(s) => {
+                self.hist_pos += 1;
+                s
+            }
+            None => return Ok(()),
+        };
+        self.seek_right()?;
+        self.clear_left()?;
+        for c in text.chars() {
+            self.insert(c)?;
+        }
+        Ok(())
+    }
+
+    fn next_history(&mut self, history: &History) -> Result<()> {
+        if self.hist_pos <= 1 {
+            self.seek_right()?;
+            self.clear_left()?;
+            self.hist_pos = 0;
+            return Ok(());
+        }
+        let text = match history.look_back(self.hist_pos - 1) {
+            Some(s) => {
+                self.hist_pos -= 1;
+                s
+            }
+            None => return Ok(()),
+        };
+        self.seek_right()?;
+        self.clear_left()?;
+        for c in text.chars() {
+            self.insert(c)?;
+        }
+        Ok(())
+    }
+}

src/error.rs

@@ -1,3 +1,8 @@
+use crate::{
+    lex::Token,
+    syntax::ExpandError,
+    topo::{Glyph, Position},
+};
 use std::io;
 use thiserror::Error;
 use windows::Win32::Foundation::{GetLastError, BOOL};
@@ -9,9 +14,126 @@ pub enum Error {
 
     #[error("i/o error: {0}")]
     IOError(#[from] io::Error),
+}
+
+#[derive(Error, Debug)]
+pub enum InputError {
+    #[error("unrecognized control character: {0}")]
+    UnrecognizedControlCharacter(u8),
+
+    #[error("input record cannot convert to control character because it is an up event")]
+    ControlCharactersOnlyGoDownNotUp,
+
+    #[error("unrecognized escape sequence: {0}")]
+    BadEscapeSequence(String),
+
+    #[error("fart")]
+    UnexpectedInputRecordDuringEscapeParting,
+}
+
+#[derive(Debug, Error)]
+pub enum LexError {
+    #[error("unexpected character {g} at {pos:?}", g = .0.glyph, pos = .0.position)]
+    UnexpectedCharacter(Glyph),
+
+    #[error("unexpected character {g} at {pos:?} while lexing a bare string", g = .0.glyph, pos = .0.position)]
+    UnexpectedCharacterInBareString(Glyph),
+
+    #[error("unexpected character {g} at {pos:?} while lexing a glob", g = .0.glyph, pos = .0.position)]
+    UnexpectedCharacterInGlob(Glyph),
+
+    #[error("unexpected eof")]
+    UnexpectedEOF(Position),
 
-    #[error("input error: {0}")]
-    InputError(String),
+    #[error("not yet supported: {1}")]
+    NotYetSupported(Position, String),
+}
+
+impl LexError {
+    pub fn not_yet(p: Position, msg: &str) -> Self {
+        LexError::NotYetSupported(p, msg.to_string())
+    }
+
+    fn position(&self) -> Position {
+        use LexError::*;
+        match self {
+            UnexpectedCharacter(g) => g.position,
+            UnexpectedCharacterInBareString(g) => g.position,
+            UnexpectedCharacterInGlob(g) => g.position,
+            UnexpectedEOF(p) => *p,
+            NotYetSupported(p, _) => *p,
+        }
+    }
+}
+
+#[derive(Debug, Error)]
+pub enum ParseError {
+    #[error("lex error at line {line}, column {col}", line=.0.position().line, col=.0.position().column)]
+    LexError(#[from] LexError),
+
+    #[error("Unexpected Token: {0:?}")]
+    UnexpectedToken(Token),
+
+    #[error("Illegal attempt to climb parse tree while already at root")]
+    AtRootAlready,
+
+    #[error("Illegal attempt to climb barse tree when target parent has already been dropped")]
+    ParentIsGone,
+
+    #[error("Illegal attempt to double-borrow a node")]
+    BorrowError(#[from] std::cell::BorrowMutError),
+
+    #[error("Illegal attempt to push a value as a child to a terminal value")]
+    PushOntoTerminal,
+
+    #[error("Statement node has no children")]
+    StatementIsEmpty,
+
+    #[error("dangling")]
+    DanglingElements,
+
+    #[error("shell expansion error")]
+    ExpansionError(#[from] ExpandError),
+
+    #[error("you wouldn't parse a semicolon")]
+    WhyParseSemicolon,
+}
+
+#[derive(Debug, Error)]
+pub enum ExecError {
+    #[error("failed waiting on child process '{name}' ({pid})")]
+    ProcessWaitError {
+        name: String,
+        pid: u32,
+        #[source]
+        source: io::Error,
+    },
+
+    #[error("failed to spawn '{name}' as a child process")]
+    ProcessSpawnError {
+        name: String,
+        #[source]
+        source: io::Error,
+    },
+
+    #[error("i/o error")]
+    IOError(#[from] std::io::Error),
+
+    #[error("value type error: {0}")]
+    ValueTypeError(String),
+
+    #[error("error: {0}")]
+    Misc(String),
+}
+
+impl ExecError {
+    pub fn type_error<S: Into<String>>(msg: S) -> Self {
+        Self::ValueTypeError(msg.into())
+    }
+
+    pub fn new<S: Into<String>>(msg: S) -> Self {
+        Self::Misc(msg.into())
+    }
 }
 
 impl Error {
@@ -26,10 +148,6 @@ impl Error {
             Err(Error::last_error())
         }
     }
-
-    pub fn input_error<S: Into<String>>(msg: S) -> Self {
-        Error::InputError(msg.into())
-    }
 }
 
 impl From<Error> for std::io::Error {

src/ext.rs

@@ -1,66 +0,0 @@
-mod command;
-mod tail;
-mod which;
-mod printenv;
-mod echo;
-
-pub use command::Command;
-pub use echo::Echo;
-pub use tail::Tail;
-pub use which::Which;
-pub use printenv::Printenv;
-
-/*
-Posix Shell builtins:
-
-  alias bg cd command false fc fg getopts hash jobs kill
-  newgrp pwd read true type ulimit umask unalias wait
-
-Bourne Shell builtins:
-
-  :         - do nothing except expand arguments and perform redirections
-  .         - read and execute a file in the current shell context
-  break     - exit from a loop
-  cd        - change the current working directory to directory
-  continue  - resume the next iteration of a loop
-  eval      - evaluate the arguments as a single command
-  exec      - replace the shell without creating a new process
-  exit      - exits the process with a status
-  export    - exports environment variables
-  getopts   - used by shell scripts to parse arguments
-  hash      - displays the hash table used by the shell to map command names to files
-  pwd       - prints the absolute path of the current directory
-  readonly  - mark each name as readonly so that they cannot be reassigned
-  return    - causes a shell function to stop execution and return a value
-  shift     - shifts the position parameters to the left by n
-  test      - evaluate a conditional expression and return a status of 0 or 1
-  times     - print out the user and system times used by the shell and its children. sorry, what the fuck is this
-  trap      - execute commands when a given signal is received
-  umask     - set the shell process's file creation mask
-  unset     - clears variable or function names
-
-Bash Builtins:
-
-  alias     - creates an alias for a command
-  bind      - adds key bindings
-  builtin   - access a builtin function even if it has been masked by another function
-  caller    - tells you what line number you're executing?
-  command   - runs a command with a given name, ignoring shell functions
-  declare   - declare variables and give them attributes
-  echo      - echos the outputs
-  enable    - enable and disable builtin shell commands
-  help      - display help text about builtin commands
-  let       - perform arithmetic on shell variables
-  local     - create local variables
-  logout    - exits a login shell with a status
-  mapfile   - read lines from stdin or a file into an array
-  printf    - formats arguments using a format string
-  read      - reads one line from stdin or from a file
-  readarray - read lines from stdin into an array or something
-  source    - executes the script in the current shell
-  type      - tells you if a thing is an alias, function, builtin, or file command
-  typeset   - synonym for declare, included for korn shell compatibility
-  ulimit    - provides control over the resources available to the processes started by the shell
-  unalias   - clears an alias
-
-*/

src/ext/command.rs

@@ -1,7 +0,0 @@
-use anyhow::Result;
-
-pub trait Command {
-    fn name() -> String;
-    fn create() -> Self;
-    fn exec(&mut self, args: Vec<&str>) -> Result<bool>;
-}

src/ext/echo.rs

@@ -1,19 +0,0 @@
-use crate::ext::Command;
-use anyhow::Result;
-
-pub struct Echo {}
-
-impl Command for Echo {
-    fn name() -> String {
-        String::from("echo")
-    }
-
-    fn create() -> Self {
-        Self {}
-    }
-
-    fn exec(&mut self, args: Vec<&str>) -> Result<bool> {
-        println!("{}", args.join(" "));
-        Ok(true)
-    }
-}

src/ext/printenv.rs

@@ -1,33 +0,0 @@
-use crate::ext::Command;
-use anyhow::Result;
-
-pub struct Printenv {}
-
-impl Command for Printenv {
-    fn name() -> String {
-        String::from("printenv")
-    }
-
-    fn create() -> Self {
-        Self {}
-    }
-
-    fn exec(&mut self, args: Vec<&str>) -> Result<bool> {
-        if args.len() > 0 {
-            let name = args[0];
-            match std::env::var(name) {
-                Ok(val) => {
-                    println!("{}", val);
-                    Ok(true)
-                }
-                Err(e) => {
-                    println!("ERROR {}", e);
-                    Ok(false)
-                }
-            }
-        } else {
-            println!("which variable you fucking dork");
-            Ok(false)
-        }
-    }
-}

src/ext/which.rs

@@ -1,34 +0,0 @@
-use crate::ext::Command;
-use anyhow::Result;
-
-pub struct Which {}
-
-impl Command for Which {
-    fn name() -> String {
-        String::from("which")
-    }
-
-    fn create() -> Self {
-        Self {}
-    }
-
-    fn exec(&mut self, args: Vec<&str>) -> Result<bool> {
-        if args.len() > 0 {
-            let path = std::env::var("path").unwrap();
-            let dirs: Vec<&str> = path.split(";").collect();
-            for d in dirs {
-                let dir = std::path::Path::new(d);
-                let fname = dir.join(args[0]).with_extension("exe");
-                if fname.exists() && fname.is_file() {
-                    println!("{}", fname.to_str().unwrap());
-                    return Ok(true);
-                }
-            }
-            println!("not found: {}", args[0]);
-            Ok(false)
-        } else {
-            println!("what do you want to look for?");
-            Ok(false)
-        }
-    }
-}

src/history.rs

@@ -0,0 +1,45 @@
+pub struct History {
+    events: Vec<String>,
+}
+
+impl History {
+    pub fn new() -> Self {
+        Self { events: Vec::new() }
+    }
+
+    pub fn add<S: Into<String>>(&mut self, event: S) {
+        let text = event.into();
+        if text.is_empty() {
+            return;
+        }
+        self.events.push(text);
+    }
+
+    pub fn look_back(&self, idx: usize) -> Option<&str> {
+        if idx == 0 || idx > self.events.len() {
+            return None;
+        }
+        Some(&self.events[self.events.len() - idx])
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn new_history() {
+        let mut history = History::new();
+        assert_eq!(history.look_back(1), None);
+        assert_eq!(history.look_back(0), None);
+
+        history.add("Hello");
+        assert_eq!(history.look_back(1), Some("Hello"));
+        assert_eq!(history.look_back(0), None);
+
+        history.add("Hello again");
+        assert_eq!(history.look_back(2), Some("Hello"));
+        assert_eq!(history.look_back(1), Some("Hello again"));
+        assert_eq!(history.look_back(0), None);
+    }
+}

src/input.rs

@@ -1,132 +1,132 @@
-use crate::{error::Error, key, log::*};
+use crate::{
+    error::{Error, InputError},
+    key,
+    log::*,
+};
 use anyhow::{Context, Result};
-use windows::Win32::Foundation::HANDLE;
-use windows::Win32::System::Console;
-use macros::escapes;
-
-#[allow(dead_code)]
-fn log_input_mode(mode: Console::CONSOLE_MODE) {
-    // Characters read by the ReadFile or ReadConsole function are written to the active screen
-    // buffer as they are typed into the console. This mode can be used only if the
-    // ENABLE_LINE_INPUT mode is also enabled.
-    if (mode & Console::ENABLE_ECHO_INPUT).0 > 0 {
-        debug!("Echo Input:             Enabled");
-    } else {
-        debug!("Echo Input:             Disabled");
-    }
+use log::error;
+use std::{
+    cell::{RefCell, RefMut},
+    collections::VecDeque,
+    fmt,
+    rc::{Rc, Weak},
+};
+use windows::Win32::{Foundation::HANDLE, System::Console};
 
-    // When enabled, text entered in a console window will be inserted at the current cursor
-    // location and all text following that location will not be overwritten. When disabled, all
-    // following text will be overwritten.
-    if (mode & Console::ENABLE_INSERT_MODE).0 > 0 {
-        debug!("Insert Mode:            Enabled");
-    } else {
-        debug!("Insert Mode:            Disabled");
+/// retrieves a Windows Console handle using the Win32 apis
+fn stdin_handle() -> Result<HANDLE> {
+    unsafe {
+        let handle = Console::GetStdHandle(Console::STD_INPUT_HANDLE)
+            .context("unable to get stdin handle")?;
+        Ok(handle)
     }
-
-    // The ReadFile or ReadConsole function returns only when a carriage return character is read.
-    // If this mode is disabled, the functions return when one or more characters are available.
-    if (mode & Console::ENABLE_LINE_INPUT).0 > 0 {
-        debug!("Line Input Mode:        Enabled");
-    } else {
-        debug!("Line Input Mode:        Disabled");
 }
 
-    // If the mouse pointer is within the borders of the console window and the window has the
-    // keyboard focus, mouse events generated by mouse movement and button presses are placed in
-    // the input buffer. These events are discarded by ReadFile or ReadConsole, even when this mode
-    // is enabled. The ReadConsoleInput function can be used to read MOUSE_EVENT input records from
-    // the input buffer.
-    if (mode & Console::ENABLE_MOUSE_INPUT).0 > 0 {
-        debug!("Mouse Input:            Enabled");
-    } else {
-        debug!("Mouse Input:            Disabled");
+/// checks to see whether the raw underling console input record is the beginning of an escape
+/// sequence
+fn is_escape_start(record: &Console::INPUT_RECORD) -> bool {
+    if record.EventType as u32 == Console::KEY_EVENT {
+        unsafe {
+            let event = record.Event.KeyEvent;
+            event.wVirtualKeyCode == 0 && event.uChar.UnicodeChar == 27 && event.bKeyDown.as_bool()
         }
-
-    // CTRL+C is processed by the system and is not placed in the input buffer. If the input buffer
-    // is being read by ReadFile or ReadConsole, other control keys are processed by the system and
-    // are not returned in the ReadFile or ReadConsole buffer. If the ENABLE_LINE_INPUT mode is
-    // also enabled, backspace, carriage return, and line feed characters are handled by the
-    // system.
-    if (mode & Console::ENABLE_PROCESSED_INPUT).0 > 0 {
-        debug!("Processed Input:        Enabled");
     } else {
-        debug!("Processed Input:        Disabled");
+        false
     }
-
-    // This flag enables the user to use the mouse to select and edit text. To enable this mode,
-    // use ENABLE_QUICK_EDIT_MODE | ENABLE_EXTENDED_FLAGS. To disable this mode, use
-    // ENABLE_EXTENDED_FLAGS without this flag.
-    if (mode & Console::ENABLE_QUICK_EDIT_MODE).0 > 0 {
-        debug!("Quick Edit Mode:        Enabled");
-    } else {
-        debug!("Quick Edit Mode:        Disabled");
 }
 
-    // User interactions that change the size of the console screen buffer are reported in the
-    // console's input buffer. Information about these events can be read from the input buffer by
-    // applications using the ReadConsoleInput function, but not by those using ReadFile or
-    // ReadConsole.
-    if (mode & Console::ENABLE_WINDOW_INPUT).0 > 0 {
-        debug!("Window Input:           Enabled");
+/// checks to see if a record is indicating the end of an escape sequence
+fn is_escape_done(record: &Console::INPUT_RECORD) -> bool {
+    if record.EventType as u32 == Console::KEY_EVENT {
+        unsafe {
+            let event = record.Event.KeyEvent;
+            // This is a key up event for the physical escape key
+            event.wVirtualKeyCode == 27
+                && event.uChar.UnicodeChar == 27
+                && !event.bKeyDown.as_bool()
+        }
     } else {
-        debug!("Window Input:           Disabled");
+        false
+    }
 }
 
-    // Setting this flag directs the Virtual Terminal processing engine to convert user input
-    // received by the console window into Console Virtual Terminal Sequences that can be retrieved
-    // by a supporting application through ReadFile or ReadConsole functions.
-    //
-    // The typical usage of this flag is intended in conjunction with
-    // ENABLE_VIRTUAL_TERMINAL_PROCESSING on the output handle to connect to an application that
-    // communicates exclusively via virtual terminal sequences.
-    if (mode & Console::ENABLE_VIRTUAL_TERMINAL_INPUT).0 > 0 {
-        debug!("Virtual Terminal Input: Enabled");
+/// attempts to convert a record into a character that would appear in an escape sequence
+fn as_escape_character(record: &Console::INPUT_RECORD) -> Option<char> {
+    if record.EventType as u32 != Console::KEY_EVENT {
+        None
     } else {
-        debug!("Virtual Terminal Input: Disabled");
+        unsafe {
+            let n = record.Event.KeyEvent.uChar.UnicodeChar as u32;
+            let c = char::from_u32(n);
+            c
+        }
     }
 }
 
-fn stdin_handle() -> Result<HANDLE> {
+/// checks to see if a console record is indicating that the control key has been pressed or
+/// depressed. Note that this has no analogue in the vt100 specification, this is purely a Windows
+/// thing.
+fn as_ctrl_toggle(record: &Console::INPUT_RECORD) -> Option<bool> {
+    if record.EventType as u32 == Console::KEY_EVENT {
         unsafe {
-        let handle = Console::GetStdHandle(Console::STD_INPUT_HANDLE)
-            .context("unable to get stdin handle")?;
-        Ok(handle)
+            let event = record.Event.KeyEvent;
+            if event.wVirtualKeyCode == 17 {
+                return Some(event.bKeyDown.as_bool());
             }
         }
+    }
+    None
+}
 
+/// a handle to a terminal's stream of input events. This is analagous to the input portion of a
+/// vt100 tty terminal.
+///
+/// This implementation specifically is implementing the Windows API for Console input.
+///
+/// In the Windows Console API, console inputs are communicated using struct values having type
+/// [INPUT_RECORD](https://learn.microsoft.com/en-us/windows/console/input-record-str).
 pub struct Reader {
     input: HANDLE,
-    // this area in memory is where the Windows API will write events read off of the keyboard.
-    buf: [Console::INPUT_RECORD; 32],
-    // the number of valid input record items in the buf since last read
-    buf_len: u32,
-    // the position of our current indexer into the input record buffer
-    buf_idx: usize,
 
+    /// this scratch buffer is used as a shared memory location for communicating with the kernel.
+    /// When we request input records, the windows kernel writes them into this buffer.
+    scratch: [Console::INPUT_RECORD; 32],
+
+    /// A lookahead buffer of unprocessed events. If we request input events from Windows and there
+    /// are more than one event, we put the unprocessed events into this lookahead buffer to reduce
+    /// the number of syscalls we're making.
+    lookahead: VecDeque<Console::INPUT_RECORD>,
+
+    /// whether or not the control key is pressed, i think?
     ctrl: bool,
+
+    pub(crate) escapes: EscapeCursor,
 }
 
 impl Reader {
     pub fn new() -> Result<Self> {
+        let escapes = build_prefix_tree();
         let v = Self {
-            buf: [Console::INPUT_RECORD::default(); 32],
-            buf_len: 0,
-            buf_idx: 0,
+            scratch: [Console::INPUT_RECORD::default(); 32],
+            lookahead: VecDeque::new(),
             input: stdin_handle()?,
             ctrl: false,
+            escapes,
         };
+
         v.reset()?;
         Ok(v)
     }
 
     pub fn reset(&self) -> Result<()> {
+        // https://learn.microsoft.com/en-us/windows/console/setconsolemode
         let mut mode = Console::CONSOLE_MODE(0);
         unsafe {
-            Console::SetConsoleCP(65001);
+            // set the console's code page to 65001, which is the code page for utf-8
+            Error::check(Console::SetConsoleCP(65001))?;
 
-            let handle = stdin_handle()?;
-            Error::check(Console::GetConsoleMode(handle, &mut mode))?;
+            // retrieve the current console mode
+            Error::check(Console::GetConsoleMode(self.input, &mut mode))?;
 
             // allow terminal input characters
             mode |= Console::ENABLE_VIRTUAL_TERMINAL_INPUT;
@@ -143,188 +143,165 @@ impl Reader {
             // enable mouse input
             mode |= Console::ENABLE_MOUSE_INPUT;
 
-            Error::check(Console::SetConsoleMode(handle, mode))?;
-            Error::check(Console::GetConsoleMode(handle, &mut mode))?;
-            // debug!("Stdin details:");
-            // log_input_mode(mode);
+            // enable reporting of window resize events
+            mode |= Console::ENABLE_WINDOW_INPUT;
+
+            Error::check(Console::SetConsoleMode(self.input, mode))?;
         }
         Ok(())
     }
 
     pub fn next(&mut self) -> Result<Event> {
-        let rec = self.next_rec()?;
-        if rec.EventType as u32 == Console::KEY_EVENT {
+        let record = self.next_record()?;
+
+        if let Some(ctrl_toggle) = as_ctrl_toggle(&record) {
+            self.ctrl = ctrl_toggle;
+            debug!("ctrl {on}", on = if self.ctrl { "ON" } else { "OFF" });
+            return self.next();
+        }
+
+        // This is a little weird but on a vt100 terminal, when you held down control you could
+        // send ascii values directly. So ctrl-a is actually the ascii value of 1, which is the
+        // "start of heading" character, and ctrl-d is actually the ascii value of 4, which is the
+        // "end of transmission" character.
+        //
+        // Now the way that the Windows Console api works is that it sends events for both key down
+        // and key up. Here's the rub: the vt100 did not send any key up events. The vt100 didn't
+        // send anything at all if you tapped and released control, but the Windows Console api
+        // would send a ctrl key down and ctrl key up event.
+        if self.ctrl && record.EventType as u32 == Console::KEY_EVENT {
             unsafe {
-                let event = rec.Event.KeyEvent;
-                if event.wVirtualKeyCode == 0 && event.uChar.UnicodeChar == 27 {
-                    return Ok(self.next_escape_sequence()?);
+                let key_event = record.Event.KeyEvent;
+                if key_event.bKeyDown.as_bool() {
+                    match ControlCharacter::try_from(key_event) {
+                        Ok(c) => return Ok(Event::Control(c)),
+                        Err(e) => warn!("{:?}", e),
+                    }
+                }
             }
-                if event.wVirtualKeyCode == 17 {
-                    self.ctrl = event.bKeyDown.as_bool();
-                    debug!("ctrl {}", event.bKeyDown.as_bool());
         }
+
+        if is_escape_start(&record) {
+            match self.next_escape_sequence() {
+                Ok(escape) => return Ok(Event::Escape(escape)),
+                Err(e) => {
+                    error!("{e}");
+                    return self.next();
                 }
             }
-        Ok(rec.into())
         }
 
-    fn log_recs(&mut self) {
-        debug!("  +---------------------+");
-        for i in 0..self.buf_len {
-            let rec = self.buf[i as usize];
-            let e: Event = rec.into();
-            match e {
-                Event::Key(k) => debug!("  | {} |", k),
-                _ => debug!("  | {:<14?} |", &e),
+        let event: Event = record.into();
+        if matches!(event, Event::Key(key::Event { down: false, .. })) {
+            return self.next();
         }
+        Ok(event)
     }
-        debug!("  +---------------------+");
+
+    /// reads the next INPUT_RECORD value from the underlying Windows Console file descriptor.
+    fn next_record(&mut self) -> Result<Console::INPUT_RECORD> {
+        if let Some(record) = self.lookahead.pop_front() {
+            return Ok(record);
         }
 
-    fn next_rec(&mut self) -> Result<Console::INPUT_RECORD> {
-        if self.buf_idx as u32 >= self.buf_len {
+        let mut num_read: u32 = 0;
+
+        // request records from windows
         unsafe {
             Error::check(Console::ReadConsoleInputA(
                 self.input,
-                    &mut self.buf,
-                    &mut self.buf_len,
+                &mut self.scratch,
+                &mut num_read,
             ))?;
         }
-            debug!("• {}", self.buf_len);
-            self.log_recs();
-            self.buf_idx = 0;
-        }
 
-        let rec = self.buf[self.buf_idx];
-        self.buf_idx += 1;
-        return Ok(rec);
-    }
-
-    fn next_escape_sequence(&mut self) -> Result<Event> {
-        match self.next_escape_char()? {
-            '[' => match self.next_escape_char()? {
-                'A' => Ok(Event::Up),
-                'B' => Ok(Event::Down),
-                'C' => Ok(Event::Right),
-                'D' => Ok(Event::Left),
-                'H' => Ok(Event::Home),
-                'F' => Ok(Event::End),
-                '1' => match self.next_escape_char()? {
-                    '3' => match self.next_escape_char()? {
-                        ';' => match self.next_escape_char()? {
-                            '5' => match self.next_escape_char()? {
-                                'u' => Ok(Event::Drop(String::from("13;5u"))),
-                                e => Err(Error::input_error(format!("[13;5 unexpected escape char: {}", e)).into()),
-                            }
-                            e => Err(Error::input_error(format!("[13; unexpected escape char: {}", e)).into()),
-                        }
-                        e => Err(Error::input_error(format!("[13 unexpected escape char: {}", e)).into()),
-                    }
-                    '5' => match self.next_escape_char()? {
-                        '~' => Ok(Event::Drop(String::from("[15~ - F5"))),
-                        e => Err(Error::input_error(format!("[15 unexpected escape char: {}", e)).into()),
-                    }
-                    '7' => match self.next_escape_char()? {
-                        '~' => Ok(Event::Drop(String::from("[17~ - F6"))),
-                        e => Err(Error::input_error(format!("[17 unexpected escape char: {}", e)).into()),
-                    }
-                    '8' => match self.next_escape_char()? {
-                        '~' => Ok(Event::Drop(String::from("[18~ - F7"))),
-                        e => Err(Error::input_error(format!("[18 unexpected escape char: {}", e)).into()),
+        let records = &self.scratch[0..num_read as usize];
+        debug!("{num_read} records:");
+        for record in records {
+            self.lookahead.push_back(*record);
+            if record.EventType as u32 == Console::KEY_EVENT {
+                unsafe {
+                    let key: key::Event = record.Event.KeyEvent.clone().into();
+                    debug!("  {key}");
                 }
-                    '9' => match self.next_escape_char()? {
-                        '~' => Ok(Event::Drop(String::from("[19~ - F8"))),
-                        e => Err(Error::input_error(format!("[19 unexpected escape char: {}", e)).into()),
+            } else {
+                debug!("  -");
             }
-                    e => Err(Error::input_error(format!("[1 unexpected escape char: {}", e)).into()),
-                },
-                '2' => match self.next_escape_char()? {
-                    '0' => match self.next_escape_char()? {
-                        '~' => Ok(Event::Drop(String::from("[20~ - F9"))),
-                        e => Err(Error::input_error(format!("[20 unexpected escape char: {}", e)).into()),
         }
-                    '1' => match self.next_escape_char()? {
-                        '~' => Ok(Event::Drop(String::from("[21~ - F10"))),
-                        e => Err(Error::input_error(format!("[20 unexpected escape char: {}", e)).into()),
+        Ok(self.lookahead.pop_front().unwrap())
     }
-                    '3' => match self.next_escape_char()? {
-                        '~' => Ok(Event::Drop(String::from("[23~ - F11"))),
-                        e => Err(Error::input_error(format!("[23 unexpected escape char: {}", e)).into()),
+
+    fn next_escape_sequence(&mut self) -> Result<Escape> {
+        self.escapes.reset();
+        loop {
+            let record = self.next_record()?;
+            if is_escape_start(&record) {
+                continue;
             }
-                    '4' => match self.next_escape_char()? {
-                        '~' => Ok(Event::Drop(String::from("[24~ - F12"))),
-                        e => Err(Error::input_error(format!("[24 unexpected escape char: {}", e)).into()),
+            if is_escape_done(&record) {
+                if self.escapes.is_at_root() {
+                    return Ok(Escape::Empty);
+                } else {
+                    panic!();
                 }
-                    e => Err(Error::input_error(format!("[2 unexpected escape char: {}", e)).into()),
             }
-                e => Err(Error::input_error(format!("[ unexpected escape char: {}", e)).into()),
-            },
-            'O' => match self.next_escape_char()? {
-                'P' => Ok(Event::Drop(String::from("OP -  F1"))),
-                'Q' => Ok(Event::Drop(String::from("OQ -  F2"))),
-                'R' => Ok(Event::Drop(String::from("OR -  F3"))),
-                'S' => Ok(Event::Drop(String::from("OS -  F4"))),
-                e => Err(Error::input_error(format!("O unexpected escape char: {}", e)).into()),
-            }
-            e => Err(Error::input_error(format!("unexpected escape char: {}", e)).into()),
-        }
-    }
-
-    // fn take_bracket(&mut self) -> Result<()> {
-    //     let rec = self.next_rec()?;
-    //     if rec.EventType as u32 != Console::KEY_EVENT {
-    //         Err(Error::input_error("failed to read escape sequence: not a key event").into())
-    //     } else {
-    //         unsafe {
-    //             let event = rec.Event.KeyEvent;
-    //             if event.wVirtualKeyCode == 0 && event.uChar.UnicodeChar == 91 {
-    //                 Ok(())
-    //             } else {
-    //                 Err(Error::input_error("failed to read escape sequence: not a [").into())
-    //             }
-    //         }
-    //     }
-    // }
-
-    fn next_escape_char(&mut self) -> Result<char> {
-        let rec = self.next_rec()?;
-        if rec.EventType as u32 != Console::KEY_EVENT {
-            Err(
-                Error::input_error("failed to read char in escape sequence: not a key event")
-                    .into(),
-            )
-        } else {
-            unsafe {
-                let n = rec.Event.KeyEvent.uChar.UnicodeChar as u32;
-                let c = char::from_u32(n);
-                c.ok_or_else(|| {
-                    let msg = format!("escape key value is not a valid unicode character: {}", n);
-                    Error::input_error(msg).into()
-                })
+            let c = as_escape_character(&record)
+                .ok_or(InputError::UnexpectedInputRecordDuringEscapeParting)?;
+            match self.escapes.step(c) {
+                EscapeStep::Continue => {}
+                EscapeStep::End(escape) => return Ok(escape),
+                EscapeStep::Abort(s) => return Err(InputError::BadEscapeSequence(s).into()),
             }
         }
     }
 }
 
+/// Event represents all of the events that may be seen as input by the shell process. Note that
+/// the set of events described here includes both in-band and out of band events, which is because
+/// that's how it works in the vt100 spec. It's a little funky but that's because it's reflecting a
+/// spec from the 70's.
 #[derive(Debug)]
 pub enum Event {
+    /// The process has received focus
     Focus(bool),
+
+    /// This is a windows Menu event. This might be skippable?
     Menu(u32),
+
+    /// A Key press. Key events associate to keys on the keyboard that are typically in-band, that
+    /// is, they're associated with specific characters
     Key(key::Event),
+
+    /// an event from the user's mouse, such as a mouse movement or click
     Mouse { x: i16, y: i16 },
+
+    /// a resize event to inform us that the visual window of our process has changed
     Size,
-    Left,
-    Right,
-    Up,
-    Down,
-    Home,
-    End,
-    Drop(String),
+
+    /// A decoded ANSI Escape Sequence. At the Terminal level, an Escape sequence is defined by a
+    /// string of characters instead of just one character. Escape Sequences are used to
+    /// communicate a variety of edit-related functionality such as navigation.
+    Escape(Escape),
+
+    /// An ASCII Controll Character.
+    Control(ControlCharacter),
 }
 
-const ALT_KEYS: u32 = 0x0002 | 0x0001;
-const CTRL_KEYS: u32 = 0x0008 | 0x0004;
-const SHIFT_PRESSED: u32 = 0x0010;
+impl fmt::Display for Event {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        use Event::*;
+        match self {
+            Key(k) => write!(f, "Event<Key {k}>"),
+            Control(c) => write!(f, "Event<Control {c:?}>"),
+            Escape(e) => write!(f, "Event<Escape {e:?}>"),
+            Focus(true) => write!(f, "Event<focus>"),
+            Focus(false) => write!(f, "Event<unfocus>"),
+            Menu(n) => write!(f, "Event<Menu {n}>"),
+            Mouse { x, y } => write!(f, "Event<Mouse {x},{y}>"),
+            Size => write!(f, "Event<Size>"),
+        }
+    }
+}
 
 impl From<Console::INPUT_RECORD> for Event {
     fn from(rec: Console::INPUT_RECORD) -> Self {
@@ -339,24 +316,7 @@ impl From<Console::INPUT_RECORD> for Event {
                 let event = rec.Event.MenuEvent;
                 Event::Menu(event.dwCommandId)
             },
-            Console::KEY_EVENT => {
-                // https://learn.microsoft.com/en-us/windows/win32/inputdev/virtual-key-codes
-                unsafe {
-                    let event = rec.Event.KeyEvent;
-                    let mstate = event.dwControlKeyState;
-                    let c = char::from_u32(event.uChar.UnicodeChar as u32).unwrap_or('💀');
-
-                    Event::Key(key::Event {
-                        down: event.bKeyDown.as_bool(),
-                        repeats: event.wRepeatCount,
-                        code: key::CODES[event.wVirtualKeyCode as usize],
-                        alt: mstate & ALT_KEYS > 0,
-                        ctrl: mstate & CTRL_KEYS > 0,
-                        shift: mstate & SHIFT_PRESSED > 0,
-                        char: c,
-                    })
-                }
-            }
+            Console::KEY_EVENT => unsafe { Event::Key(rec.Event.KeyEvent.clone().into()) },
             Console::MOUSE_EVENT => {
                 // OK I think it's safe to ignore these events since we're using the terminal
                 // escape sequences. I think we never see them because terminal.exe is going to
@@ -381,6 +341,206 @@ impl From<Console::INPUT_RECORD> for Event {
     }
 }
 
+/// A reference to a target node in a prefix tree, used for manipulating the prefix tree
+#[derive(Debug, Clone)]
+pub struct EscapeCursor {
+    target: Rc<EscapeNode>,
+    root: Rc<EscapeNode>,
+}
+
+/// A node in a prefix tree. This prefix tree is used to parse strings into escape sequences. This
+/// prefix tree is special in that there are no values in the intermediate nodes of the tree.
+#[derive(Debug)]
+pub enum EscapeNode {
+    Root {
+        children: RefCell<Vec<Rc<EscapeNode>>>,
+    },
+    Nonterminal {
+        c: char,
+        parent: Weak<EscapeNode>,
+        children: RefCell<Vec<Rc<EscapeNode>>>,
+    },
+    Terminal {
+        c: char,
+        parent: Weak<EscapeNode>,
+        v: Escape,
+    },
+}
+
+impl EscapeNode {
+    /// Creates a new prefix tree mapping character sequences to structured escape codes
+    pub fn new() -> EscapeCursor {
+        let root = Rc::new(EscapeNode::Root {
+            children: RefCell::new(Vec::new()),
+        });
+        EscapeCursor {
+            target: Rc::clone(&root),
+            root,
+        }
+    }
+
+    fn char(&self) -> char {
+        match self {
+            EscapeNode::Nonterminal { c, .. } | EscapeNode::Terminal { c, .. } => *c,
+            _ => panic!(),
+        }
+    }
+
+    fn children(&self) -> RefMut<Vec<Rc<EscapeNode>>> {
+        match self {
+            EscapeNode::Root { children } | EscapeNode::Nonterminal { children, .. } => {
+                children.borrow_mut()
+            }
+            _ => panic!(),
+        }
+    }
+
+    fn parent(&self) -> Option<Rc<EscapeNode>> {
+        match self {
+            EscapeNode::Root { .. } => None,
+            EscapeNode::Nonterminal { parent, .. } => parent.upgrade(),
+            EscapeNode::Terminal { parent, .. } => parent.upgrade(),
+        }
+    }
+
+    fn child(&self, c: char) -> Option<Rc<EscapeNode>> {
+        for child in self.children().iter_mut() {
+            if child.char() == c {
+                return Some(Rc::clone(child));
+            }
+        }
+        None
+    }
+}
+
+impl EscapeCursor {
+    /// advances our cursor by one step. We look at the current position and descend the tree into
+    /// the node described by the target character. If that node is a terminal node, we return that
+    /// node's value.
+    fn step(&mut self, c: char) -> EscapeStep {
+        let child = match self.target.child(c) {
+            Some(c) => c,
+            None => {
+                let path = self.path();
+                return EscapeStep::Abort(format!("{path}{c}"));
+            }
+        };
+        match child.as_ref() {
+            EscapeNode::Terminal { v, .. } => {
+                self.reset();
+                EscapeStep::End(*v)
+            }
+            _ => {
+                self.target = child;
+                EscapeStep::Continue
+            }
+        }
+    }
+
+    fn add_step(&mut self, c: char) {
+        match self.target.child(c) {
+            Some(child) => self.target = child,
+            None => {
+                for child in self.target.clone().children().iter() {
+                    if child.char() == c {
+                        self.target = Rc::clone(child);
+                        return;
+                    }
+                }
+                let child = Rc::new(EscapeNode::Nonterminal {
+                    c,
+                    parent: Rc::downgrade(&self.target),
+                    children: RefCell::new(Vec::new()),
+                });
+                self.target.children().push(Rc::clone(&child));
+                self.target = child;
+            }
+        }
+    }
+
+    /// adds a terminal node into the tree as a child of the current node
+    fn add_terminal(&mut self, c: char, v: Escape) {
+        for child in self.target.children().iter_mut() {
+            if child.char() == c {
+                panic!();
+            }
+        }
+        let child = Rc::new(EscapeNode::Terminal {
+            c,
+            parent: Rc::downgrade(&self.target),
+            v,
+        });
+        self.target.children().push(child);
+    }
+
+    /// resets the cursor back to the top of the tree
+    fn reset(&mut self) {
+        self.target = Rc::clone(&self.root);
+    }
+
+    fn is_at_root(&self) -> bool {
+        Rc::ptr_eq(&self.target, &self.root)
+    }
+
+    /// inserts a sequence -> Escape mapping into the prefix tree
+    fn insert(&mut self, sequence: &str, v: Escape) {
+        self.reset();
+        let mut chars = sequence.chars().peekable();
+        loop {
+            let c = chars.next().unwrap();
+            if chars.peek().is_none() {
+                self.add_terminal(c, v);
+                return;
+            }
+            self.add_step(c);
+        }
+    }
+
+    /// renders as a string the path that takes us to the node to which we are currently pointed
+    fn path(&self) -> String {
+        let mut cursor = self.clone();
+        let mut chars = Vec::new();
+        while !cursor.is_at_root() {
+            chars.push(cursor.target.char());
+            cursor.target = cursor.target.parent().unwrap();
+        }
+        chars.iter().rev().collect()
+    }
+}
+
+enum EscapeStep {
+    Continue,
+    Abort(String),
+    End(Escape),
+}
+
+/// generates a prefix tree used for parsing escape sequences
+macro_rules! escapes {
+    ($($sequence:literal $variant:tt)*) => {
+        /// a parsed escape sequence
+        #[derive(Debug, Clone, Copy)]
+        pub enum Escape {
+            Empty,
+            $(
+                $variant,
+            )*
+        }
+
+        /// assembles our prefix tree. Generally only needs to be called once. I think this could
+        /// actually be done in a proc macro that builds the prefix tree at compile time instead of
+        /// at run time.
+        fn build_prefix_tree() -> EscapeCursor {
+            let mut tree = EscapeNode::new();
+            $(
+                let v = Escape::$variant;
+                tree.insert($sequence, v);
+            )*
+            tree.reset();
+            tree
+        }
+    };
+}
+
 escapes! {
     "[A" Up
     "[B" Down
@@ -392,29 +552,119 @@ escapes! {
     "[5~" PageUp
     "[6~" PageDown
 
-    "[13;2u" Shift_Enter
-    "[13;5u" Ctrl_Enter
-    "[13;6u" Ctrl_Shift_Enter
-
-    "[1;2P" Shift_F1
-    "[1;2Q" Shift_F2
-    "[1;5P" Ctrl_F1
-    "[1;6P" Ctrl_Shift_F1
-    "[1;3P" Alt_F1
-    "[1;4P" Shift_Alt_F1
+    "[13;2u" ShiftEnter
+    "[13;3u" AltEnter
+    "[13;5u" CtrlEnter
+    "[13;6u" CtrlShiftEnter
 
     "OP" F1
+    "[1;2P" ShiftF1
+    "[1;3P" AltF1
+    "[1;4P" ShiftAltF1
+    "[1;5P" CtrlF1
+    "[1;6P" CtrlShiftF1
+    "[1;8P" CtrlAltShiftF1
+
     "OQ" F2
+    "[1;2Q" ShiftF2
+
     "OR" F3
     "OS" F4
 
     "[15~" F5
-    "[15;2~" Shift_F5
+    "[15;2~" ShiftF5
     "[17~" F6
     "[18~" F7
     "[19~" F8
+    "[20~" F9
+    "[21~" F10
+    "[23~" F11
     "[24~" F12
-    "[53;5u" Ctrl_Shift_5
+    "[53;5u" CtrlShift5
+}
+
+/// a control character. Control characters are single individual ascii characters that represent
+/// out of band signalling.
+#[derive(Debug)]
+pub enum ControlCharacter {
+    Null,
+    StartOfHeading,
+    StartOfText,
+    EndOfText,
+    EndOfTransmission,
+    Enquiry,
+    Acknowledge,
+    Bell,
+    Backspace,
+    Tab,
+    Linefeed,
+    VTab,
+    Formfeed,
+    CarriageReturn,
+    ShiftOut,
+    ShiftIn,
+    DataLinkEscape,
+    DeviceControl1,
+    DeviceControl2,
+    DeviceControl3,
+    DeviceControl4,
+    NegativeAcknowledge,
+    SynchronousIdle,
+    EndOfTransmissionBlock,
+    Cancel,
+    EndOfMedium,
+    Substitute,
+    Esc,
+    FileSeparator,
+    GroupSeparator,
+    RecordSeparator,
+    UnitSeparator,
+}
+
+impl TryFrom<Console::KEY_EVENT_RECORD> for ControlCharacter {
+    type Error = InputError;
+
+    fn try_from(v: Console::KEY_EVENT_RECORD) -> Result<Self, Self::Error> {
+        if !v.bKeyDown.as_bool() {
+            return Err(InputError::ControlCharactersOnlyGoDownNotUp);
+        }
+        use ControlCharacter::*;
+        unsafe {
+            match v.uChar.AsciiChar.0 {
+                0 => Ok(Null),
+                1 => Ok(StartOfHeading),
+                2 => Ok(StartOfText),
+                3 => Ok(EndOfText),
+                4 => Ok(EndOfTransmission),
+                5 => Ok(Enquiry),
+                6 => Ok(Acknowledge),
+                7 => Ok(Bell),
+                8 => Ok(Backspace),
+                9 => Ok(Tab),
+                10 => Ok(Linefeed),
+                11 => Ok(VTab),
+                12 => Ok(Formfeed),
+                13 => Ok(CarriageReturn),
+                14 => Ok(ShiftOut),
+                15 => Ok(ShiftIn),
+                16 => Ok(DataLinkEscape),
+                17 => Ok(DeviceControl1),
+                18 => Ok(DeviceControl2),
+                19 => Ok(DeviceControl3),
+                20 => Ok(DeviceControl4),
+                21 => Ok(NegativeAcknowledge),
+                22 => Ok(SynchronousIdle),
+                23 => Ok(EndOfTransmissionBlock),
+                24 => Ok(Cancel),
+                25 => Ok(EndOfMedium),
+                26 => Ok(Substitute),
+                27 => Ok(Esc),
+                28 => Ok(FileSeparator),
+                29 => Ok(GroupSeparator),
+                30 => Ok(RecordSeparator),
+                31 => Ok(UnitSeparator),
+                n => Err(InputError::UnrecognizedControlCharacter(n)),
+            }
+        }
+    }
 }
-/*
-*/

src/interactive.rs

@@ -0,0 +1,128 @@
+use crate::{
+    edit,
+    history::History,
+    log::*,
+    output,
+    run::{self, Eval},
+    syntax::parse,
+};
+
+use std::{
+    error::Error,
+    io::{self, Write},
+    path::{Path, PathBuf},
+};
+
+use anyhow::Result;
+use dirs;
+
+/// An interactive session. The Session object is the top-level object used to control an
+/// interactive terminal session.
+pub struct Session {
+    pub editor: edit::Editor,
+    pub stdout: output::Writer,
+    pub stderr: output::Writer,
+}
+
+impl Session {
+    pub fn new() -> Result<Self> {
+        Ok(Self {
+            editor: edit::Editor::new()?,
+            stdout: output::Writer::stdout()?,
+            stderr: output::Writer::stderr()?,
+        })
+    }
+
+    pub fn run(mut self) -> Result<()> {
+        let mut state = run::State::new();
+        let mut ctx = run::Context {
+            stdout: self.stdout.clone(),
+            stderr: self.stderr.clone(),
+            state: &mut state,
+        };
+        let mut history = History::new();
+
+        info!("» shell session start --------");
+        loop {
+            self.editor.show_prompt()?;
+            let text = match self.editor.read_command(&mut history)? {
+                Some(text) => text,
+                None => break,
+            };
+            history.add(text.clone());
+            let command = match parse(&text) {
+                Ok(ast) => ast,
+                Err(e) => {
+                    self.render_error(e)?;
+                    continue;
+                }
+            };
+            if let Err(e) = command.eval(&mut ctx) {
+                self.render_error(e)?;
+            }
+        }
+        info!("» exit");
+        self.stdout.newline()?;
+        Ok(())
+    }
+
+    pub fn enable_logging<P>(&self, path: P)
+    where
+        P: AsRef<Path>,
+    {
+        let log_path = self.expand_path(path);
+        match Log::file(log_path) {
+            Ok(f) => {
+                let target = Box::leak(Box::new(f));
+                _ = set_logger(target).map(|()| set_max_level(LevelFilter::Debug));
+            }
+            Err(e) => {
+                println!("did not open log file: {}", e);
+            }
+        }
+    }
+
+    pub fn expand_path<P: AsRef<Path>>(&self, p: P) -> PathBuf {
+        let p = p.as_ref();
+
+        match p.to_str() {
+            Some(s) => {
+                if s.len() == 0 || !s.starts_with('~') {
+                    return p.to_path_buf();
+                }
+            }
+            None => {
+                return p.to_path_buf();
+            }
+        }
+
+        let mut parts = p.components();
+        let first = parts.next().unwrap().as_os_str().to_str().unwrap();
+        if first == "~" {
+            dirs::home_dir().unwrap().join(parts)
+        } else {
+            let my_home = dirs::home_dir().unwrap();
+            let home_root = my_home.parent().unwrap();
+            let first = &first[1..];
+            let other_home = home_root.join(first);
+            other_home.join(parts)
+        }
+    }
+
+    pub fn render_error<E: Error>(&mut self, e: E) -> io::Result<()> {
+        self.render_error_helper(e, 0)?;
+        Ok(())
+    }
+
+    fn render_error_helper<E: Error>(&mut self, e: E, depth: u8) -> io::Result<()> {
+        if depth > 0 {
+            writeln!(self.stdout, "  {e}")?;
+        } else {
+            writeln!(self.stdout, "{e}:")?;
+        }
+        if let Some(cause) = e.source() {
+            self.render_error_helper(cause, depth + 1)?;
+        }
+        Ok(())
+    }
+}

src/key.rs

@@ -1,14 +1,18 @@
 use std::fmt;
+use windows::Win32::System::Console;
 
-#[derive(Debug, PartialEq, Clone, Copy)]
+/// an abstract keycode
+#[derive(Debug, PartialEq, Eq, Clone, Copy)]
 pub struct Code {
-    /// The integer value of the keycode
+    /// The integer value of the keycode, as defined by the Windows api. These associate to windows
+    /// virtual key codes.
     pub val: u16,
 
     /// The unicode symbol that represents the keycode, if any
     pub sym: Option<char>,
 }
 
+/// An individual keypress event
 #[derive(Debug)]
 pub struct Event {
     /// True for key press events, false for key release events
@@ -17,10 +21,26 @@ pub struct Event {
     /// The number of times this event has happened in sequence
     pub repeats: u16,
 
-    /// The virtual key code for the keyboard event
+    /// The virtual keycode for the keyboard event. This represents the associated character
+    /// pressed on a keyboard, not the physical button. For example, on an AZERTY keyboard,
+    /// pressing the key whose legend says A but is in the position of the Q key on a QWERTY
+    /// keyboard,
+    ///
+    /// For more info, see here:
+    /// https://learn.microsoft.com/en-us/windows/win32/inputdev/virtual-key-codes
     pub code: Code,
 
-    /// The unicode character, or 💀 if not applicable
+    /// The hardware-provided scancode. This is the location of the physical button, with no
+    /// relationship to the user's chosen layout.
+    pub scancode: u16,
+
+    /// the untranslated windows virtual keycode
+    pub keycode: u16,
+
+    /// The unicode character of the Event. Note this these correspond to virtual terminal
+    /// sequences. For example, when you press F1, you get an escape sequence of [OP, you'll see
+    /// the chars O and P but not related to their keys, because they're virtual keys. Hey wait a
+    /// second, that means I have to be folding the escape sequences into events.
     pub char: char,
 
     /// Whether or not one of the CTRL keys was held when the event was triggered
@@ -33,27 +53,74 @@ pub struct Event {
     pub shift: bool,
 }
 
+// HEY where did these come from who left these here
+const ALT_KEYS: u32 = 0x0002 | 0x0001;
+const CTRL_KEYS: u32 = 0x0008 | 0x0004;
+const SHIFT_PRESSED: u32 = 0x0010;
+
+impl From<Console::KEY_EVENT_RECORD> for Event {
+    fn from(record: Console::KEY_EVENT_RECORD) -> Self {
+        unsafe {
+            let mstate = record.dwControlKeyState;
+            let c = char::from_u32(record.uChar.UnicodeChar as u32).unwrap_or('💀');
+            let keycode = codes::lookup(record.wVirtualKeyCode as usize);
+
+            Self {
+                down: record.bKeyDown.as_bool(),
+                repeats: record.wRepeatCount,
+                code: keycode,
+                scancode: record.wVirtualScanCode,
+                keycode: record.wVirtualKeyCode,
+                alt: mstate & ALT_KEYS > 0,
+                ctrl: mstate & CTRL_KEYS > 0,
+                shift: mstate & SHIFT_PRESSED > 0,
+                char: c,
+            }
+        }
+    }
+}
+
 impl fmt::Display for Event {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         let down = if self.down { '↓' } else { '↑' };
         let sym = match self.code.sym {
             Some(c) => c,
-            None => '∅',
+            None => '·',
         };
-        let ctrl = if self.ctrl { '⎈' } else { '·' };
-        let alt = if self.alt { '⎇' } else { '·' };
-        let shift = if self.shift { '⇧'} else { '·' };
-        let c = if self.char.is_control() { '·' } else { self.char };
-        write!(f, "{} {} {} {} {: >3} {} {: >1} {: >3}", down, ctrl, alt, shift, self.code.val, sym, c, self.char as u16)
+        let ctrl = if self.ctrl { 'C' } else { '·' };
+        let alt = if self.alt { 'A' } else { '·' };
+        let shift = if self.shift { 'S' } else { '·' };
+        let glyph = if !self.char.is_control() {
+            self.char
+        } else if self.char as u32 == 27 {
+            '⁝'
+        } else {
+            '·'
+        };
+        write!(
+            f,
+            "{down} {ctrl} {alt} {shift} {glyph} {charcode: <3} {sym} {code: <3} {keycode: <3} {scancode: <3}",
+            charcode = self.char as u32,
+            code = self.code.val,
+            keycode = self.keycode,
+            scancode = self.scancode,
+        )
     }
 }
 
-/// CODES contains a lookup table for key codes. Note that this is a sparse array and not all
-/// values associate to valid key codes.
-pub static CODES: [Code; 256] = gen_codes();
-
-macro_rules! keycodes {
+macro_rules! codes {
     ($($val:literal $name:ident $sym:literal)*) => {
+
+        /// stores our key code constants
+        pub mod codes {
+            use super::Code;
+            $(
+                #[allow(unused)]
+                pub const $name: Code = Code{val: $val, sym: Some($sym)};
+            )*
+
+            /// generates a table of key codes
+            /// https://learn.microsoft.com/en-us/windows/win32/inputdev/virtual-key-codes
             const fn gen_codes() -> [Code; 256] {
                 let mut codes = [Code{val: 0, sym: None}; 256];
                 let mut i = 0 as usize;
@@ -68,39 +135,53 @@ macro_rules! keycodes {
                 codes
             }
 
-        $(
-            #[allow(dead_code)]
-            pub const $name: Code = Code{val: $val, sym: Some($sym)};
-        )*
+            /// Lookup table to retrieve keycodes by their numeric value
+            const INDEX: [Code; 256] = gen_codes();
+
+            /// Translates the numeric value of a win32 VirtualKeyCode into a key::Code value
+            pub const fn lookup(vk_code: usize) -> Code {
+                INDEX[vk_code]
+            }
+        }
     }
 }
 
-keycodes! {
-    0x07 NOTBACKSPACE '⌫'
+codes! {
+    0x01 MOUSE_LEFT ' '
+    0x02 MOUSE_RIGHT ' '
+    0x03 CTRL_BREAK ' ' // control-break processing
+    0x04 MIDDLE_MOUSE ' '
+    0x05 X1_MOUSE ' '
+    0x06 X2_MOUSE ' ' // 0x07 is reserved
     0x08 BACKSPACE '⌫'
-    0x09 TAB '↹'
-    // 0x0A-0B 	Reserved
-    // 0x0C CLEAR
-    0x0D ENTER '↩'
-    // 0x0E-0F 	Undefined
+    0x09 TAB '↹' // 0x0A-0B 	Reserved
+    0x0C CLEAR ' '
+    0x0D ENTER '↩' // 0x0E-0F 	Unassigned
     0x10 SHIFT '⇧'
     0x11 CTRL '⎈'
     0x12 ALT '⎇'
-    0x13 BREAK '⎉'
+    0x13 PAUSE '⎉'
     0x14 CAPS_LOCK '⇪'
-    // 0x15 IME Kana mode
-    // 0x15 IME Hanguel mode (maintained for compatibility; use VK_HANGUL)
-    // 0x15 IME Hangul mode
-    // 0x16 IME On
-    // 0x17 IME Junja mode
-    // 0x18 IME final mode
-    // 0x19 IME Hanja mode
-    // 0x19 IME Kanji mode
-    // 0x1A IME Off
-    // 0x1C IME convert
+    0x15 KANA_MODE ' '
     0x1B ESC '⎋'
     0x20 SPACE '␣'
+    0x21 PAGE_UP '↟'
+    0x22 PAGE_DOWN '↡'
     0x23 END '⇲'
+    0x25 LEFT '←'
+    0x26 UP '↑'
+    0x27 RIGHT '→'
+    0x28 DOWN '↓'
+    0x30 NUM_0 '0'
+    0x31 NUM_1 '1'
+    0x32 NUM_2 '2'
+    0x33 NUM_3 '3'
+    0x34 NUM_4 '4'
+    0x35 NUM_5 '5'
+    0x36 NUM_6 '6'
+    0x37 NUM_7 '7'
+    0x38 NUM_8 '8'
+    0x39 NUM_9 '9'
     0x41 A 'a'
     0x42 B 'b'
     0x43 C 'c'
@@ -127,144 +208,8 @@ keycodes! {
     0x58 X 'x'
     0x59 Y 'y'
     0x5A Z 'z'
-    0x30 NUM_0 '0'
-    0x31 NUM_1 '1'
-    0x32 NUM_2 '2'
-    0x33 NUM_3 '3'
-    0x34 NUM_4 '4'
-    0x35 NUM_5 '5'
-    0x36 NUM_6 '6'
-    0x37 NUM_7 '7'
-    0x38 NUM_8 '8'
-    0x39 NUM_9 '9'
-    // 0x70 F1
-    // 0x71 F2
-    // 0x72 F3
-    // 0x73 F4
-    // 0x74 F5
-    // 0x75 F6
-    // 0x76 F7
-    // 0x77 F8
-    // 0x78 F9
-    // 0x79 F10
-    // 0x7A F11
-    // 0x7B F12
-    // 0x7C F13
-    // 0x7D F14
-    // 0x7E F15
-    // 0x7F F16
-    // 0x80 F17
-    // 0x81 F18
-    // 0x82 F19
-    // 0x83 F20
-    // 0x84 F21
-    // 0x85 F22
-    // 0x86 F23
-    // 0x87 F24
-    0x21 PAGE_UP '↟'
-    0x22 PAGE_DOWN '↡'
-    0x25 LEFT '←'
-    0x26 UP '↑'
-    0x27 RIGHT '→'
-    0x28 DOWN '↓'
     0xA0 LEFT_SHIFT '⇧'
     0xA1 RIGHT_SHIFT '⇧'
     0xBE PERIOD '.'
     0xDE QUOTE '\''
 }
-
-/*
-VK_NONCONVERT 	0x1D 	IME nonconvert
-VK_ACCEPT 	0x1E 	IME accept
-VK_MODECHANGE 	0x1F 	IME mode change request
-VK_HOME 	0x24 	HOME key
-VK_SELECT 	0x29 	SELECT key
-VK_PRINT 	0x2A 	PRINT key
-VK_EXECUTE 	0x2B 	EXECUTE key
-VK_SNAPSHOT 	0x2C 	PRINT SCREEN key
-VK_INSERT 	0x2D 	INS key
-VK_DELETE 	0x2E 	DEL key
-VK_HELP 	0x2F 	HELP key
-- 	0x3A-40 	Undefined
-VK_LWIN 	0x5B 	Left Windows key (Natural keyboard)
-VK_RWIN 	0x5C 	Right Windows key (Natural keyboard)
-VK_APPS 	0x5D 	Applications key (Natural keyboard)
-- 	0x5E 	Reserved
-VK_SLEEP 	0x5F 	Computer Sleep key
-VK_NUMPAD0 	0x60 	Numeric keypad 0 key
-VK_NUMPAD1 	0x61 	Numeric keypad 1 key
-VK_NUMPAD2 	0x62 	Numeric keypad 2 key
-VK_NUMPAD3 	0x63 	Numeric keypad 3 key
-VK_NUMPAD4 	0x64 	Numeric keypad 4 key
-VK_NUMPAD5 	0x65 	Numeric keypad 5 key
-VK_NUMPAD6 	0x66 	Numeric keypad 6 key
-VK_NUMPAD7 	0x67 	Numeric keypad 7 key
-VK_NUMPAD8 	0x68 	Numeric keypad 8 key
-VK_NUMPAD9 	0x69 	Numeric keypad 9 key
-VK_MULTIPLY 	0x6A 	Multiply key
-VK_ADD 	0x6B 	Add key
-VK_SEPARATOR 	0x6C 	Separator key
-VK_SUBTRACT 	0x6D 	Subtract key
-VK_DECIMAL 	0x6E 	Decimal key
-VK_DIVIDE 	0x6F 	Divide key
-- 	0x88-8F 	Unassigned
-VK_NUMLOCK 	0x90 	NUM LOCK key
-VK_SCROLL 	0x91 	SCROLL LOCK key
-    0x92-96 	OEM specific
-- 	0x97-9F 	Unassigned
-VK_LCONTROL 	0xA2 	Left CONTROL key
-VK_RCONTROL 	0xA3 	Right CONTROL key
-VK_LMENU 	0xA4 	Left ALT key
-VK_RMENU 	0xA5 	Right ALT key
-VK_BROWSER_BACK 	0xA6 	Browser Back key
-VK_BROWSER_FORWARD 	0xA7 	Browser Forward key
-VK_BROWSER_REFRESH 	0xA8 	Browser Refresh key
-VK_BROWSER_STOP 	0xA9 	Browser Stop key
-VK_BROWSER_SEARCH 	0xAA 	Browser Search key
-VK_BROWSER_FAVORITES 	0xAB 	Browser Favorites key
-VK_BROWSER_HOME 	0xAC 	Browser Start and Home key
-VK_VOLUME_MUTE 	0xAD 	Volume Mute key
-VK_VOLUME_DOWN 	0xAE 	Volume Down key
-VK_VOLUME_UP 	0xAF 	Volume Up key
-VK_MEDIA_NEXT_TRACK 	0xB0 	Next Track key
-VK_MEDIA_PREV_TRACK 	0xB1 	Previous Track key
-VK_MEDIA_STOP 	0xB2 	Stop Media key
-VK_MEDIA_PLAY_PAUSE 	0xB3 	Play/Pause Media key
-VK_LAUNCH_MAIL 	0xB4 	Start Mail key
-VK_LAUNCH_MEDIA_SELECT 	0xB5 	Select Media key
-VK_LAUNCH_APP1 	0xB6 	Start Application 1 key
-VK_LAUNCH_APP2 	0xB7 	Start Application 2 key
-- 	0xB8-B9 	Reserved
-VK_OEM_1 	0xBA 	Used for miscellaneous characters; it can vary by keyboard. For the US standard keyboard, the ';:' key
-VK_OEM_PLUS 	0xBB 	For any country/region, the '+' key
-VK_OEM_COMMA 	0xBC 	For any country/region, the ',' key
-VK_OEM_MINUS 	0xBD 	For any country/region, the '-' key
-VK_OEM_PERIOD 	0xBE 	For any country/region, the '.' key
-VK_OEM_2 	0xBF 	Used for miscellaneous characters; it can vary by keyboard. For the US standard keyboard, the '/?' key
-VK_OEM_3 	0xC0 	Used for miscellaneous characters; it can vary by keyboard. For the US standard keyboard, the '`~' key
-- 	0xC1-D7 	Reserved
-- 	0xD8-DA 	Unassigned
-VK_OEM_4 	0xDB 	Used for miscellaneous characters; it can vary by keyboard. For the US standard keyboard, the '[{' key
-VK_OEM_5 	0xDC 	Used for miscellaneous characters; it can vary by keyboard. For the US standard keyboard, the '\|' key
-VK_OEM_6 	0xDD 	Used for miscellaneous characters; it can vary by keyboard. For the US standard keyboard, the ']}' key
-VK_OEM_7 	0xDE 	Used for miscellaneous characters; it can vary by keyboard. For the US standard keyboard, the 'single-quote/double-quote' key
-VK_OEM_8 	0xDF 	Used for miscellaneous characters; it can vary by keyboard.
-- 	0xE0 	Reserved
-    0xE1 	OEM specific
-VK_OEM_102 	0xE2 	The <> keys on the US standard keyboard, or the \\| key on the non-US 102-key keyboard
-    0xE3-E4 	OEM specific
-VK_PROCESSKEY 	0xE5 	IME PROCESS key
-    0xE6 	OEM specific
-VK_PACKET 	0xE7 	Used to pass Unicode characters as if they were keystrokes. The VK_PACKET key is the low word of a 32-bit Virtual Key value used for non-keyboard input methods. For more information, see Remark in KEYBDINPUT, SendInput, WM_KEYDOWN, and WM_KEYUP
-- 	0xE8 	Unassigned
-    0xE9-F5 	OEM specific
-VK_ATTN 	0xF6 	Attn key
-VK_CRSEL 	0xF7 	CrSel key
-VK_EXSEL 	0xF8 	ExSel key
-VK_EREOF 	0xF9 	Erase EOF key
-VK_PLAY 	0xFA 	Play key
-VK_ZOOM 	0xFB 	Zoom key
-VK_NONAME 	0xFC 	Reserved
-VK_PA1 	0xFD 	PA1 key
-VK_OEM_CLEAR 	0xFE 	Clear key
-*/

src/lex.rs

@@ -0,0 +1,380 @@
+use crate::{
+    error::LexError,
+    topo::{Glyph, Glyphs, Position},
+};
+use std::{collections::VecDeque, fmt, ops::Range};
+
+/// A Lexeme is the text of a given [Token]. The lexeme contains no information about the Token's
+/// meaning or type; it is just a fancy string with position information.
+#[derive(PartialEq, Clone)]
+pub struct Lexeme {
+    elems: Vec<Glyph>,
+}
+
+impl Lexeme {
+    /// The area of the input text covered by this lexeme. This might return none of the Lexeme is
+    /// an empty string.
+    fn span(&self) -> Option<Range<Position>> {
+        if self.elems.is_empty() {
+            return None;
+        }
+        Some(Range {
+            start: self.elems[0].position,
+            end: self.elems[self.elems.len() - 1].position,
+        })
+    }
+
+    fn text(&self) -> String {
+        self.elems.as_slice().iter().map(|tg| tg.glyph).collect()
+    }
+}
+
+impl fmt::Debug for Lexeme {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
+        let span = match self.span() {
+            Some(span) => span,
+            None => return write!(f, "<empty Lexeme>"),
+        };
+
+        write!(
+            f,
+            "<{text} @{start_line}:{start_column}-{end_line}:{end_column}>",
+            start_line = span.start.line,
+            start_column = span.start.column,
+            end_line = span.end.line,
+            end_column = span.end.column,
+            text = self.text(),
+        )
+    }
+}
+
+impl fmt::Display for Lexeme {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
+        write!(f, "{}", self.text())
+    }
+}
+
+impl From<Vec<Glyph>> for Lexeme {
+    fn from(v: Vec<Glyph>) -> Self {
+        Self { elems: v }
+    }
+}
+
+/// The smallest lexical unit of our language. A token represents a single element of program
+/// source text, such as an identifier or a piece of punctuation.
+#[allow(dead_code)]
+#[derive(Debug, PartialEq, Clone)]
+pub enum Token {
+    /// A bare word: a sequence of characters without any quotes. A bare word is always not a glob.
+    Word(Lexeme),
+
+    /// A bare word containing 1 or more of the special characters ? or *
+    Glob(Lexeme),
+
+    Semi(Glyph),
+
+    Pipe(Glyph),
+}
+
+impl Token {
+    /// Checks whether or not another token has the same contents as this Token. The eq
+    /// implementation will also consider positional information, whereas the `same` function does
+    /// not.
+    #[allow(unused)]
+    fn same(&self, other: &Self) -> bool {
+        use Token::*;
+
+        println!(
+            "check same self: {self:?} other: {other:?}",
+            self = self.text(),
+            other = other.text()
+        );
+
+        match (self, other) {
+            (Word(a), Word(b)) => a.text() == b.text(),
+            (Glob(a), Glob(b)) => a.text() == b.text(),
+            _ => false,
+        }
+    }
+
+    fn text(&self) -> String {
+        use Token::*;
+
+        match self {
+            Word(lexeme) | Glob(lexeme) => lexeme.text(),
+            Pipe(glyph) | Semi(glyph) => String::from(glyph.glyph),
+        }
+    }
+}
+
+/// Tokenizer splits some input [Glyphs] into [Token] values. The Tokenize has no lookahead or
+/// buffering.
+struct Tokenizer<'text> {
+    source: Glyphs<'text>,
+}
+
+impl<'text> Tokenizer<'text> {
+    /// creates a new tokenizer for some given input source text
+    pub fn new(text: &'text str) -> Self {
+        Self {
+            source: Glyphs::new(text),
+        }
+    }
+
+    /// produces the next token in our input source text. If we've hit EOF, this will return None.
+    fn next_token(&mut self) -> Option<Result<Token, LexError>> {
+        self.source.yeet_whitespace();
+        let next = self.source.next()?;
+
+        match next.glyph {
+            _ if next.is_word() => Some(self.lex_bare_string(vec![next])),
+            _ if next.is_glob() => Some(self.lex_glob(vec![next])),
+            '|' => Some(Ok(Token::Pipe(next))),
+            '@' => Some(self.lex_var(vec![next])),
+            '\'' => Some(self.lex_raw_string(vec![next])),
+            '"' => Some(self.lex_string_literal(vec![])),
+            ';' => Some(Ok(Token::Semi(next))),
+            _ => Some(Err(LexError::UnexpectedCharacter(next))),
+        }
+    }
+
+    fn lex_bare_string(&mut self, mut progress: Vec<Glyph>) -> Result<Token, LexError> {
+        while let Some(next) = self.source.peek() {
+            match next.glyph {
+                _ if next.glyph.is_whitespace() => break,
+                _ if next.is_word() => progress.push(self.source.pop()?),
+                _ if next.is_glob() => {
+                    progress.push(self.source.pop()?);
+                    return self.lex_glob(progress);
+                }
+                ';' | '|' => break,
+                _ => {
+                    return Err(LexError::UnexpectedCharacterInBareString(
+                        self.source.pop()?,
+                    ))
+                }
+            }
+        }
+
+        if progress.is_empty() {
+            Err(LexError::UnexpectedEOF(self.source.next_position))
+        } else {
+            Ok(Token::Word(progress.into()))
+        }
+    }
+
+    fn lex_glob(&mut self, mut progress: Vec<Glyph>) -> Result<Token, LexError> {
+        while let Some(next) = self.source.peek() {
+            match next.glyph {
+                ';' => break,
+                _ if next.glyph.is_whitespace() => break,
+                _ if next.is_glob() => progress.push(self.source.pop()?),
+                // '\\' => {
+                //     self.source.pop()?;
+                //     progress.push(self.source.pop()?);
+                // }
+                _ => return Err(LexError::UnexpectedCharacterInGlob(self.source.pop()?)),
+            }
+        }
+
+        if progress.is_empty() {
+            Err(LexError::UnexpectedEOF(self.source.next_position))
+        } else {
+            Ok(Token::Glob(progress.into()))
+        }
+    }
+
+    fn lex_raw_string(&mut self, _progress: Vec<Glyph>) -> Result<Token, LexError> {
+        Err(LexError::not_yet(
+            self.source.next_position,
+            "raw strings not done yet",
+        ))
+    }
+
+    fn lex_string_literal(&mut self, mut progress: Vec<Glyph>) -> Result<Token, LexError> {
+        while let Some(next) = self.source.peek() {
+            match next.glyph {
+                _ if next.glyph.is_whitespace() => progress.push(self.source.pop()?),
+                _ if next.is_word() => progress.push(self.source.pop()?),
+                _ if next.is_glob() => progress.push(self.source.pop()?),
+                '"' => {
+                    self.source.pop()?;
+                    break;
+                }
+                _ => todo!(),
+            }
+        }
+        if progress.is_empty() {
+            Err(LexError::UnexpectedEOF(self.source.next_position))
+        } else {
+            Ok(Token::Word(progress.into()))
+        }
+    }
+
+    fn lex_var(&mut self, _progress: Vec<Glyph>) -> Result<Token, LexError> {
+        Err(LexError::not_yet(
+            self.source.next_position,
+            "variables are not done yet",
+        ))
+    }
+}
+
+impl<'text> Iterator for Tokenizer<'text> {
+    type Item = Result<Token, LexError>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.next_token()
+    }
+}
+
+/// A Lexer is responsible for converting a piece of source text into a sequence of tokens.
+pub struct Lexer<'text> {
+    source: Tokenizer<'text>,
+    lookahead: VecDeque<Token>,
+}
+
+impl<'text> Lexer<'text> {
+    pub fn new(source: &'text str) -> Self {
+        Self {
+            source: Tokenizer::new(source),
+            lookahead: VecDeque::new(),
+        }
+    }
+
+    fn fill_lookahead(&mut self, n: usize) -> Result<bool, LexError> {
+        while self.lookahead.len() < n {
+            let token = match self.source.next() {
+                Some(res) => res?,
+                None => return Ok(false),
+            };
+            self.lookahead.push_back(token);
+        }
+        Ok(true)
+    }
+
+    fn peek_at(&mut self, idx: usize) -> Result<Option<&Token>, LexError> {
+        self.fill_lookahead(idx + 1)?;
+        Ok(self.lookahead.get(idx))
+    }
+
+    pub fn peek(&mut self) -> Result<Option<&Token>, LexError> {
+        self.peek_at(0)
+    }
+}
+
+impl<'text> Iterator for Lexer<'text> {
+    type Item = Result<Token, LexError>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        match self.lookahead.pop_front() {
+            Some(token) => Some(Ok(token)),
+            None => self.source.next(),
+        }
+    }
+}
+
+/// splits a corpus into Tokens.
+#[cfg(test)]
+pub fn lex(source: &str) -> Result<Vec<Token>, LexError> {
+    Lexer::new(source).collect()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::iter::zip;
+
+    fn lexeme(txt: &str) -> Lexeme {
+        let x: Vec<Glyph> = txt
+            .chars()
+            .map(|c| Glyph {
+                glyph: c,
+                position: Position::origin(),
+                bytes: 0..0,
+            })
+            .collect();
+        x.into()
+    }
+
+    fn glob(txt: &str) -> Token {
+        Token::Glob(lexeme(txt))
+    }
+
+    fn word(txt: &str) -> Token {
+        Token::Word(lexeme(txt))
+    }
+
+    macro_rules! accept {
+    ( $($test_name:ident $input_text:literal [ $( $token:expr )* ])+) => {$(
+        #[test]
+        fn $test_name() -> Result<(), LexError> {
+            #[allow(unused_mut)]
+            let mut expected: Vec<Token> = Vec::new();
+            $( expected.push($token); )*
+
+            let lexed = lex($input_text)?;
+            assert_eq!(expected.len(), lexed.len());
+
+            for pair in zip(expected, lexed) {
+                println!("pair: {pair:?}");
+                assert!(pair.0.same(&pair.1));
+            }
+
+            Ok(())
+        }
+    )*};
+    }
+
+    macro_rules! reject {
+    ($($test_name:ident:  $input_text:literal;)+) => {$(
+        #[test]
+        fn $test_name() {
+            match lex($input_text) {
+                Ok(tokens) => {
+                    println!("output tokens: {tokens:?}");
+                    panic!("Did not encounter an expected lex error");
+                }
+                Err(e) => println!("output error: {e:?}"),
+            }
+        }
+    )*};
+    }
+
+    reject! {
+        // Vars aren't done yet
+        var: "@name";
+
+        // Single-quoted strings arne't done yet
+        strings: r"echo 'one' two";
+
+    }
+
+    accept! {
+        empty "" []
+        spaces "    " []
+        identifier "a" [ word("a") ]
+        identifier_2 "  a" [ word("a") ]
+        identifier_3 "a  " [ word("a") ]
+        identifier_4 "  a  " [ word("a") ]
+        double_quoted_strings r#"echo "one" two"# [
+            word("echo")
+            word("one")
+            word("two")
+        ]
+        file_name "poop.exe" [ word("poop.exe") ]
+        multi_idents "one two    three			four  " [
+            word("one")
+            word("two")
+            word("three")
+            word("four")
+        ]
+        glob_1 "*" [ glob("*") ]
+        glob_2 " * " [ glob("*") ]
+        glob_3 "x*" [ glob("x*") ]
+        glob_4 "*x" [ glob("*x") ]
+        glob_5 "*.py" [ glob("*.py") ]
+        mixed_1 "ls *.py" [ word("ls") glob("*.py") ]
+        abs "cd c:\\one\\two" [ word("cd") word("c:\\one\\two")]
+        home "cd ~\\stuff" [ word("cd") word("~\\stuff") ]
+    }
+}

src/line.rs

@@ -1,146 +0,0 @@
-use crate::log::*;
-use std::cmp::min;
-
-pub struct Line {
-    /// the current contents of the line
-    chars: Vec<char>,
-
-    /// the cursor position of our dit head within the vector of characters that we store as chars
-    cursor: usize,
-}
-
-impl Line {
-    pub fn new() -> Self {
-        Self {
-            chars: Vec::new(),
-            cursor: 0,
-        }
-    }
-
-    pub fn clear(&mut self) {
-        self.cursor = 0;
-        self.chars.clear();
-        self.show_debug();
-    }
-
-    pub fn pop(&mut self) -> String {
-        let s: String = self.chars.iter().collect();
-        self.clear();
-        self.show_debug();
-        s
-    }
-
-    pub fn show(&self) -> String {
-        self.chars.iter().collect()
-    }
-
-    pub fn back(&mut self, n: usize) -> bool {
-        if self.cursor > 0 {
-            if n > self.cursor {
-                self.cursor = n;
-            } else {
-                self.cursor -= n;
-            }
-            self.show_debug();
-            true
-        } else {
-            false
-        }
-    }
-
-    pub fn backspace(&mut self) -> bool {
-        if self.chars.len() > 0 {
-            if self.cursor > 0 {
-                self.cursor -= 1;
-            }
-            self.chars.remove(self.cursor);
-            self.show_debug();
-            true
-        } else {
-            false
-        }
-    }
-
-    /// removes the elements left of the cursor, returning the count of removed elements
-    pub fn clear_left(&mut self) -> usize {
-        if self.cursor > 0 {
-            let n = self.chars.drain(..self.cursor).count();
-            self.cursor = 0;
-            self.show_debug();
-            n
-        } else {
-            0
-        }
-    }
-
-    /// moves the cursor to the start of the edit line, returning the old cursor value
-    pub fn seek_left(&mut self) -> usize {
-        let n = self.cursor;
-        self.cursor = 0;
-        self.show_debug();
-        n
-    }
-
-    pub fn seek_right(&mut self) -> usize {
-        let n = self.chars.len() - self.cursor;
-        self.cursor = self.chars.len();
-        self.show_debug();
-        n
-    }
-
-    pub fn forward(&mut self, n: usize) -> bool {
-        if self.cursor < self.chars.len() {
-            self.cursor = min(self.chars.len(), self.cursor + n);
-            self.show_debug();
-            true
-        } else {
-            false
-        }
-    }
-
-    pub fn insert(&mut self, c: char) {
-        self.chars.insert(self.cursor, c);
-        self.cursor += 1;
-        self.show_debug();
-    }
-
-    pub fn tail(&self) -> String {
-        let mut start = self.cursor;
-        if start > 0 {
-            start -= 1;
-        }
-
-        let chars = &self.chars[start..];
-        chars.iter().collect()
-    }
-
-    pub fn pos(&self) -> usize {
-        self.cursor
-    }
-
-    pub fn len(&self) -> usize {
-        self.chars.len()
-    }
-
-    fn show_debug(&self) {
-        let before = if self.chars.len() > 0 {
-            self.chars[0..self.cursor].to_vec().iter().collect()
-        } else {
-            String::new()
-        };
-
-        let after = if self.chars.len() > 0 {
-            self.chars[self.cursor..].to_vec().iter().collect()
-        } else {
-            String::new()
-        };
-
-        debug!(
-            "  {: <5} {: >5} {}·{}",
-            self.cursor,
-            self.chars.len(),
-            before,
-            after
-        );
-    }
-}

src/log.rs

@@ -1,5 +1,5 @@
 use crate::error::Error;
-pub use log::{debug, error, info, set_logger, set_max_level, trace, warn, LevelFilter};
+pub use log::{debug, info, set_logger, set_max_level, warn, LevelFilter};
 
 use std::{
     fs::File,
@@ -49,19 +49,19 @@ where
                 match record.level() {
                     log::Level::Error => {
                         _ = write!(out, "\x1b[31m{}\x1b[0m\n", record.args());
-                    },
+                    }
                     log::Level::Warn => {
                         _ = write!(out, "\x1b[33m{}\x1b[0m\n", record.args());
-                    },
+                    }
                     log::Level::Info => {
                         _ = write!(out, "\x1b[37m{}\x1b[0m\n", record.args());
-                    },
+                    }
                     log::Level::Debug => {
                         _ = write!(out, "\x1b[90m{}\x1b[0m\n", record.args());
-                    },
+                    }
                     log::Level::Trace => {
                         _ = write!(out, "\x1b[36m{}\x1b[0m\n", record.args());
-                    },
+                    }
                 }
             }
         }

src/main.rs

@@ -1,205 +1,52 @@
-mod error;
-mod ext;
-mod input;
-mod key;
-mod line;
-mod log;
-mod output;
-mod parse;
-mod prompt;
-mod shell;
-
-use crate::log::*;
-use prompt::Prompt;
-use shell::Shell;
-
-use std::io::Write;
+/// builtin functions
+mod builtin;
 
-use anyhow::Result;
-
-fn main() -> Result<()> {
-    let mut shell = Shell::new()?;
-    let log_path = shell.expand_path("~/clyde.log");
-    match Log::file(log_path) {
-        Ok(f) => {
-            let target = Box::leak(Box::new(f));
-            _ = set_logger(target).map(|()| set_max_level(LevelFilter::Debug));
-        }
-        Err(e) => {
-            println!("did not open log file: {}", e);
-        }
-    }
+/// all of the errors for the clyde project live in this module
+mod error;
 
-    let prompt = Prompt::new();
-
-    prompt.print(&mut shell.output)?;
-    info!("» enter");
-    loop {
-        match shell.input.next()? {
-            input::Event::Key(event) => {
-                if event.down {
-                    if event.code.val == 0 {
-                        debug!("  {}", event);
-                    } else {
-                        warn!("  {}", event);
-                    }
-                    continue;
-                }
-                info!("  {}", event);
+/// handles input from terminals
+mod input;
 
-                if event.code == key::LEFT {
-                    shell.back(1)?;
-                    continue;
-                }
+/// defines the interactive mode
+mod interactive;
 
-                if event.code == key::RIGHT {
-                    shell.forward(1)?;
-                    continue;
-                }
+/// key presses, independent from input sources
+mod key;
 
-                if event.code == key::ENTER {
-                    shell.output.newline()?;
-                    let s = shell.line.pop();
-                    info!("◇ {}", s);
-                    let tree = parse::parse(&s)?;
-                    debug!("  {:?}", tree);
-                    shell.exec(tree.into())?;
-                    // Some commands don't leave the terminal in a clean state, so we use reset
-                    // to ensure that our input and output modes are what we expect them to be.
-                    shell.reset()?;
-                    prompt.print(&mut shell.output)?;
-                    continue;
-                }
+/// lexical analysis
+mod lex;
 
-                if event.code == key::TAB {
-                    continue;
-                }
+/// a real primitive line editor
+mod edit;
 
-                if event.code == key::BACKSPACE {
-                    if shell.line.backspace() {
-                        // move cursor back two spaces
-                        shell.output.back(2)?;
-                        let tail = format!("{} ", shell.line.tail());
-                        let n = tail.chars().count();
-                        shell.output.write(tail.as_bytes())?;
-
-                        // after writing out the tail, rewind by the number of characters in
-                        // the tail
-                        if n > 1 {
-                            // let text = format!("\x1b[{}D", n - 1);
-                            shell.output.back(n - 1)?;
-                            // output.write(text.as_bytes())?;
-                        } else {
-                            // honestly I can't remember how I figured this out
-                            shell.output.write(b" \x1b[1D")?;
-                        }
-                    }
-                    continue;
-                }
+mod history;
 
-                // CTRL-D to exit
-                if event.ctrl && event.code == key::D {
-                    info!("» exit");
-                    shell.output.close()?;
-                    return Ok(());
-                }
+/// logging configuration
+mod log;
 
-                // CTRL-J to draw a cool little dot
-                if event.ctrl && event.code == key::J {
-                    debug!("⎈ j: dot");
-                    // red bullet
-                    shell
-                        .output
-                        .write(String::from("\x1b[31m\u{2022}\x1b[0m").as_bytes())?;
-                    continue;
-                }
+/// stdout control, output more generally
+mod output;
 
-                // CTRL-L to clear the screen
-                if event.ctrl && event.code == key::L {
-                    info!("» clear");
-                    shell.output.clear()?;
-                    prompt.print(&mut shell.output)?;
-                    shell.output.write(shell.line.show().as_bytes())?;
-                    shell.output.back(shell.line.len() - shell.line.pos())?;
-                    shell.reset()?;
-                    continue;
-                }
+/// turns our tokens into parse trees
+mod parse;
 
-                // CTRL-U to erase to the beginning of the line
-                if event.ctrl && event.code == key::U {
-                    info!("» clear left");
-                    let n = shell.line.clear_left();
-                    if n > 0 {
-                        // move left by the number of elements removed
-                        shell.output.back(n)?;
-                        // draw the elements remaining, followed by a space for each removed
-                        // element
-                        let kept = shell.line.show();
-                        let text = format!("{}{:width$}", kept, "", width = n);
-                        shell.output.write(text.as_bytes())?;
-                        shell.output.back(n + kept.chars().count())?;
-                    }
-                    continue;
-                }
+/// why is prompt a whole module what am i doing
+mod prompt;
 
-                // CTRL-A to move to the beginning of the line
-                if event.ctrl && event.code == key::A {
-                    shell.seek_left()?;
-                    continue;
-                }
+/// the runtime state of the shell process
+mod run;
 
-                // CTRL-E to move to the end of the line
-                if event.ctrl && event.code == key::E {
-                    shell.seek_right()?;
-                    continue;
-                }
+/// syntax and semantic analysis
+mod syntax;
 
-                // TODO: something better here, this is crappy. I should be checking characters
-                // based on their unicode categories, not this garbo
-                if !event.char.is_control() {
-                    shell.line.insert(event.char);
+/// topoglyph is a real word, i promise
+mod topo;
 
-                    let tail = shell.line.tail();
-                    let n = tail.chars().count();
+fn main() -> anyhow::Result<()> {
+    let session = interactive::Session::new()?;
 
-                    // write everything from the current line cursor out to the output buffer.
-                    shell.output.write(tail.as_bytes())?;
-                    if n > 1 {
-                        // if we wrote more than one character, because we weren't at the end, we
-                        // need to rewind the terminal cursor to where it was.
-                        shell.output.back(n - 1)?;
-                    }
-                    continue;
-                }
+    #[cfg(debug_assertions)]
+    session.enable_logging("~/clyde.log");
 
-                warn!("‽ {}", event);
-            }
-            input::Event::Left => shell.back(1)?,
-            input::Event::Right => shell.forward(1)?,
-            input::Event::Up => debug!("⛬ ↑"),
-            input::Event::Down => debug!("⛬ ↓"),
-            input::Event::Home => shell.seek_left()?,
-            input::Event::End => shell.seek_right()?,
-            input::Event::Focus(true) => {}
-            input::Event::Focus(false) => {}
-            input::Event::Menu(_command_id) => {}
-            input::Event::Drop(seq) => debug!("? {}", seq),
-            input::Event::Mouse { .. } => {}
-            input::Event::Size => {}
+    session.run()
 }
-    }
-}
-
-/*
-
-> ls
-foo
-bar
-whatever
-
-> ls 
-
-
-
-
-*/

src/output.rs

@@ -1,99 +1,9 @@
-use crate::{error::Error, log::*};
+use crate::error::Error;
 use anyhow::{Context, Result};
 use std::io::{self, Write};
-use windows::Win32::{
-    Foundation::{CloseHandle, HANDLE},
-    System::Console,
-};
-
-#[allow(dead_code)]
-fn log_output_mode(mode: Console::CONSOLE_MODE) {
-    // Characters written by the WriteFile or WriteConsole function or echoed by the ReadFile or
-    // ReadConsole function are parsed for ASCII control sequences, and the correct action is
-    // performed. Backspace, tab, bell, carriage return, and line feed characters are processed. It
-    // should be enabled when using control sequences or when ENABLE_VIRTUAL_TERMINAL_PROCESSING is
-    // set.
-    if (mode & Console::ENABLE_PROCESSED_OUTPUT).0 > 0 {
-        debug!("Processed Output:    Enabled");
-    } else {
-        debug!("Processed Output:    Disabled");
-    }
-
-    // When writing with WriteFile or WriteConsole or echoing with ReadFile or ReadConsole, the
-    // cursor moves to the beginning of the next row when it reaches the end of the current row.
-    // This causes the rows displayed in the console window to scroll up automatically when the
-    // cursor advances beyond the last row in the window. It also causes the contents of the
-    // console screen buffer to scroll up (../discarding the top row of the console screen buffer)
-    // when the cursor advances beyond the last row in the console screen buffer. If this mode is
-    // disabled, the last character in the row is overwritten with any subsequent characters.
-    if (mode & Console::ENABLE_WRAP_AT_EOL_OUTPUT).0 > 0 {
-        debug!("Wrap at EOL:         Enabled");
-    } else {
-        debug!("Wrap at EOL:         Disabled");
-    }
-
-    // When writing with WriteFile or WriteConsole, characters are parsed for VT100 and similar
-    // control character sequences that control cursor movement, color/font mode, and other
-    // operations that can also be performed via the existing Console APIs. For more information,
-    // see Console Virtual Terminal Sequences.
-    //
-    // Ensure ENABLE_PROCESSED_OUTPUT is set when using this flag.
-    if (mode & Console::ENABLE_VIRTUAL_TERMINAL_PROCESSING).0 > 0 {
-        debug!("Terminal Processing: Enabled");
-    } else {
-        debug!("Terminal Processing: Disabled");
-    }
-
-    // When writing with WriteFile or WriteConsole, this adds an additional state to end-of-line
-    // wrapping that can delay the cursor move and buffer scroll operations.
-    //
-    // Normally when ENABLE_WRAP_AT_EOL_OUTPUT is set and text reaches the end of the line, the
-    // cursor will immediately move to the next line and the contents of the buffer will scroll up
-    // by one line. In contrast with this flag set, the cursor does not move to the next line, and
-    // the scroll operation is not performed. The written character will be printed in the final
-    // position on the line and the cursor will remain above this character as if
-    // ENABLE_WRAP_AT_EOL_OUTPUT was off, but the next printable character will be printed as if
-    // ENABLE_WRAP_AT_EOL_OUTPUT is on. No overwrite will occur. Specifically, the cursor quickly
-    // advances down to the following line, a scroll is performed if necessary, the character is
-    // printed, and the cursor advances one more position.
-    //
-    // The typical usage of this flag is intended in conjunction with setting
-    // ENABLE_VIRTUAL_TERMINAL_PROCESSING to better emulate a terminal emulator where writing the
-    // final character on the screen (../in the bottom right corner) without triggering an
-    // immediate scroll is the desired behavior.
-    if (mode & Console::DISABLE_NEWLINE_AUTO_RETURN).0 > 0 {
-        debug!("Newline Auto Return: Enabled");
-    } else {
-        debug!("Newline Auto Return: Disabled");
-    }
-
-    // The APIs for writing character attributes including WriteConsoleOutput and
-    // WriteConsoleOutputAttribute allow the usage of flags from character attributes to adjust the
-    // color of the foreground and background of text. Additionally, a range of DBCS flags was
-    // specified with the COMMON_LVB prefix. Historically, these flags only functioned in DBCS code
-    // pages for Chinese, Japanese, and Korean languages.
-    //
-    // With exception of the leading byte and trailing byte flags, the remaining flags describing
-    // line drawing and reverse video (../swap foreground and background colors) can be useful for
-    // other languages to emphasize portions of output.
-    //
-    // Setting this console mode flag will allow these attributes to be used in every code page on
-    // every language.
-    //
-    // It is off by default to maintain compatibility with known applications that have
-    // historically taken advantage of the console ignoring these flags on non-CJK machines to
-    // store bits in these fields for their own purposes or by accident.
-    //
-    // Note that using the ENABLE_VIRTUAL_TERMINAL_PROCESSING mode can result in LVB grid and
-    // reverse video flags being set while this flag is still off if the attached application
-    // requests underlining or inverse video via Console Virtual Terminal Sequences.
-    if (mode & Console::ENABLE_LVB_GRID_WORLDWIDE).0 > 0 {
-        debug!("LVB Grid:            Enabled");
-    } else {
-        debug!("LVB Grid:            Disabled");
-    }
-}
+use windows::Win32::{Foundation::HANDLE, System::Console};
 
+#[derive(Clone)]
 pub struct Writer {
     output: HANDLE,
 }
@@ -109,11 +19,14 @@ impl Writer {
         }
     }
 
-    pub fn close(&mut self) -> Result<()> {
+    pub fn stderr() -> Result<Self> {
         unsafe {
-            CloseHandle(self.output);
+            let handle = Console::GetStdHandle(Console::STD_ERROR_HANDLE)
+                .context("unable to get stdout handle")?;
+            let mut stdout = Self { output: handle };
+            stdout.reset()?;
+            Ok(stdout)
         }
-        Ok(())
     }
 
     pub fn reset(&mut self) -> Result<()> {
@@ -142,23 +55,25 @@ impl Writer {
         Ok(())
     }
 
+    /// clears the output buffer
     pub fn clear(&mut self) -> Result<()> {
         self.write(b"\x1b[2J\x1b[0;0H")?;
         Ok(())
     }
-
-    // pub fn hide_cursor(&mut self) -> Result<()> {
-    //     self.write(b"\x1b[?25l")?;
-    //     Ok(())
-    // }
 }
 
 impl Write for Writer {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+        let mut written = 0;
         unsafe {
-            Error::check(Console::WriteConsoleA(self.output, buf, None, None))?;
-        }
-        Ok(0)
+            Error::check(Console::WriteConsoleA(
+                self.output,
+                buf,
+                Some(&mut written),
+                None,
+            ))?;
+        }
+        Ok(written as usize)
     }
 
     fn flush(&mut self) -> io::Result<()> {

src/parse.rs

@@ -1,463 +1,352 @@
-use log::debug;
+use crate::error::ParseError;
+use crate::lex::{Lexer, Token};
 use std::{
-    fmt,
-    ops::Deref,
     cell::RefCell,
-    rc::Rc,
+    rc::{Rc, Weak},
+    sync::atomic::AtomicUsize,
 };
-use thiserror::Error;
 
-#[derive(Debug, Error)]
-pub enum Error {
-    #[error("Unexpected Token")]
-    UnexpectedToken,
-}
-
-#[allow(dead_code)]
+/// The contents of a node in our parse tree. The parse tree consists of both terminal and
+/// nonterminal symbols.
 #[derive(Debug, PartialEq)]
-pub enum Token {
-    Ident(String),
-    Pipe,
-}
+pub enum Value {
+    /// The start symbol of our parse tree. Each parse tree is rooted in a node whose value is the
+    /// start symbol. This is the only node in the tree that should utilize the start symbol.
+    Start,
 
-#[allow(dead_code)]
-fn lex<S: AsRef<str>>(text: S) -> Result<Vec<Token>, Error> {
-    Lexer::new(text.as_ref()).lex()
-}
+    /// The children of a statement symbol make up the components of what will become a statement
+    /// in our ast
+    Command,
 
-struct Lexer<'text> {
-    chars: std::str::Chars<'text>,
-    peeked: Option<char>,
+    /// Each of the tokens from the lex stage becomes a terminal node on our tree
+    Terminal(Token),
 }
 
-impl<'text> Lexer<'text> {
-    fn new(text: &'text str) -> Self {
-        Self {
-            chars: text.chars(),
-            peeked: None,
+impl Value {
+    fn is_terminal(&self) -> bool {
+        matches!(self, Value::Terminal(_))
     }
 }
 
-    fn lex(&mut self) -> Result<Vec<Token>, Error> {
-        let mut tokens = vec![];
-        while self.peek().is_some() {
-            self.skip_whitespace();
-            match self.peek() {
-                None => return Ok(tokens),
-                Some('|') => {
-                    tokens.push(Token::Pipe);
-                    self.skip();
-                }
-                Some(_) => {
-                    tokens.push(self.ident());
-                }
-            }
-        }
-        Ok(tokens)
-    }
+/// A node in a parse tree.
+#[derive(Debug)]
+pub struct Node {
+    pub id: usize,
 
-    fn skip_whitespace(&mut self) {
-        loop {
-            match self.peek() {
-                None => break,
-                Some(c) => {
-                    if c.is_whitespace() {
-                        self.skip()
-                    } else {
-                        break;
-                    }
-                }
-            }
-        }
-    }
+    /// A node may or may not have a parent node. If a node does not have a parent node, that node
+    /// is the root node of a tree.
+    parent: Option<Weak<Node>>,
 
-    fn peek(&mut self) -> Option<char> {
-        match self.peeked {
-            Some(c) => Some(c),
-            None => match self.chars.next() {
-                Some(c) => {
-                    self.peeked = Some(c);
-                    Some(c)
-                }
-                None => None,
-            },
-        }
-    }
+    /// The value of the element at this node
+    pub value: Value,
 
-    fn skip(&mut self) {
-        if self.peeked.is_some() {
-            self.peeked = None;
-        } else {
-            self.chars.next();
-        }
+    /// A node may or may not have children. Since an empty vector is a valid vector, a node
+    /// without children is represented as having an empty children vector. A node having an empty
+    /// list of children is a leaf node in a tree.
+    pub children: RefCell<Vec<Rc<Node>>>,
 }
 
-    fn ident(&mut self) -> Token {
-        let mut kept: Vec<char> = vec![];
-        loop {
-            match self.peek() {
-                None => break,
-                Some(c) => {
-                    if c.is_whitespace() {
-                        break;
-                    }
-                    kept.push(c);
-                    self.skip();
-                }
-            }
-        }
-        Token::Ident(kept.iter().collect())
+impl Node {
+    fn new() -> Cursor {
+        let root = Rc::new(Node {
+            id: next_id(),
+            parent: None,
+            value: Value::Start,
+            children: RefCell::new(Vec::new()),
+        });
+        Cursor {
+            target: Rc::clone(&root),
+            prev: root.id,
+            root,
         }
     }
 
-// struct Parser {
-//     state: Tree,
-// }
-// 
-// impl Parser {
-//     fn new() -> Self {
-//         Self {
-//             state: Tree::new(),
-//         }
-//     }
-// 
-//     fn parse(mut self, tokens: Vec<Token>) -> Result<Node, Error> {
-//         Ok(Node::empty())
-//         // for token in tokens {
-//         //     self.take(token);
-//         // }
-//         // let t = self.state.replace(Node::empty());
-//         // Ok(t.root())
-//     }
-// }
-
-#[derive(PartialEq, Clone)]
-pub enum Element {
-    Empty,
-    Command(String),
-    Literal(String),
+    pub fn is_semi(&self) -> bool {
+        matches!(self.value, Value::Terminal(Token::Semi(_)))
     }
-
-impl fmt::Debug for Element {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
-        match self {
-            Element::Empty => write!(f, "()"),
-            Element::Command(cmd) => write!(f, "cmd<{}>", cmd),
-            Element::Literal(lit) => write!(f, "lit<{}>", lit),
 }
+
+impl PartialEq for Node {
+    fn eq(&self, other: &Self) -> bool {
+        self.id == other.id
     }
 }
 
-pub struct Node {
-    pub elem: Element,
-    pub parent: Option<Rc<RefCell<Node>>>,
-    pub children: Vec<Rc<RefCell<Node>>>,
+/// Iterates through the children of a cursor node, producing new cursor positions.
+pub struct ChildIter {
+    target: Rc<Node>,
+    root: Rc<Node>,
+    idx: usize,
 }
 
-impl Node {
-    pub fn new(elem: Element) -> Self {
-        Self {
-            elem,
-            parent: None,
-            children: Vec::new(),
+impl Iterator for ChildIter {
+    type Item = Cursor;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let children = self.target.children.borrow();
+        let v = children.get(self.idx)?;
+        self.idx += 1;
+        Some(Cursor {
+            target: Rc::clone(v),
+            root: Rc::clone(&self.root),
+            prev: self.target.id,
+        })
     }
 }
 
-    pub fn empty() -> Self {
-        Self::new(Element::Empty)
+const LAST_ID: AtomicUsize = AtomicUsize::new(0);
+fn next_id() -> usize {
+    LAST_ID.fetch_add(1, std::sync::atomic::Ordering::Relaxed)
 }
 
-    pub fn child_of(parent: Rc<RefCell<Self>>, elem: Element) -> Self {
-        Self {
-            elem,
-            parent: Some(parent),
-            children: Vec::new(),
-        }
+/// Cursor values expose access to a parse tree. A cursor is logically a pointer to a single node
+/// within a parse tree. The cursor helps with the ownership structure: so long as there is a
+/// cursor to any node on the tree, the tree remains in memory. Once there are no cursors pointed
+/// at the tree, it is dropped.
+#[derive(Debug, Clone)]
+pub struct Cursor {
+    pub target: Rc<Node>,
+    root: Rc<Node>,
+    prev: usize,
 }
 
-    pub fn visit(self) -> Tree {
-        self.into()
+impl Cursor {
+    /// Climbs one level up a parse tree. The cursor is re-pointed from its current target node to
+    /// the parent of its current target node. This method fails if the cursor is already at the
+    /// root node of the parse tree.
+    pub fn up(&mut self) -> Result<(), ParseError> {
+        match &self.target.parent {
+            None => Err(ParseError::AtRootAlready),
+            Some(parent) => match parent.upgrade() {
+                Some(parent) => {
+                    self.goto(parent);
+                    Ok(())
+                }
+                None => Err(ParseError::ParentIsGone),
+            },
         }
     }
 
-impl fmt::Debug for Node {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
-        write!(f, "{:?}", self.elem)?;
-        if self.children.len() > 0 {
-            write!(f, "[")?;
-            for child in self.children.iter() {
-                write!(f, "{:?}", child.borrow())?;
-            }
-            write!(f, "]")?;
+    /// Adds a value to the children of the current target node, then descends to select that
+    /// child.
+    fn push(&mut self, v: Value) -> Result<(), ParseError> {
+        if self.target.value.is_terminal() {
+            return Err(ParseError::PushOntoTerminal);
         }
+        let node = Node {
+            id: next_id(),
+            parent: Some(Rc::downgrade(&self.target)),
+            value: v,
+            children: RefCell::new(Vec::new()),
+        };
+        let node = Rc::new(node);
+        self.target
+            .children
+            .try_borrow_mut()?
+            .push(Rc::clone(&node));
+        self.goto(node);
         Ok(())
     }
-}
-
-pub struct Tree {
-    target: Rc<RefCell<Node>>,
-}
 
-impl Tree {
-    fn new() -> Self {
-        Node::empty().into()
+    /// moves the cursor up to the root of the tree in place
+    pub fn up_to_root(&mut self) {
+        self.goto(Rc::clone(&self.root));
     }
 
-    /// Adds an element as a node as a child of the current node, then descends the tree to select
-    /// that child node. This is similar to how pushing a value changes the top element of a stack.
-    fn push(self, elem: Element) -> Self {
-        if self.is_empty() {
-            self.target.replace(Node::new(elem));
-            self
-        } else {
-            let child = Node::child_of(Rc::clone(&self.target), elem);
-            Tree{target: Rc::new(RefCell::new(child))}
-        }
+    pub fn value(&self) -> &Value {
+        &self.target.value
     }
 
-    /// Adds a child node with a given element value to the currently selected node without chaning
-    /// our selection.
-    fn append(self, elem: Element) -> Self {
-        if self.is_empty() {
-            self.target.replace(Node::new(elem));
-        } else {
-            let node = Node::child_of(Rc::clone(&self.target), elem);
-            let child = Rc::new(RefCell::new(node));
-            self.target.borrow_mut().children.push(child);
+    pub fn iter_children(&self) -> ChildIter {
+        ChildIter {
+            target: Rc::clone(&self.target),
+            root: Rc::clone(&self.root),
+            idx: 0,
         }
-        self
     }
 
-    /// Tells us whether or not the currently selected node is an empty node
-    fn is_empty(&self) -> bool {
-        self.target.borrow().elem == Element::Empty
+    #[cfg(test)]
+    fn is_root(&self) -> bool {
+        self.target.parent.is_none()
     }
 
-    fn parent(&self) -> Option<Self> {
-        self.target.borrow().parent.as_ref().map(|parent| Self {
-            target: Rc::clone(parent),
-        })
+    #[cfg(test)]
+    fn into_root(self) -> Rc<Node> {
+        Rc::clone(&self.root)
     }
 
-    fn is_root(&self) -> bool {
-        self.parent().is_none()
+    fn text_tree(&self) -> String {
+        let mut p = self.clone();
+        p.up_to_root();
+        let mut buf = String::new();
+        self.text_tree_helper(0, &mut buf);
+        buf
     }
 
-    pub fn root(self) -> Self {
-        match self.parent() {
-            Some(parent) => parent.root(),
-            None => self,
+    fn text_tree_helper(&self, depth: u32, mut buf: &mut String) {
+        let line = format!("{:?}\n", self.value());
+        *buf = buf.to_owned() + &line;
+        for child in self.iter_children() {
+            child.text_tree_helper(depth + 1, &mut buf);
         }
     }
 
-    fn peek(&self) -> Element {
-        self.target.borrow().elem.clone()
+    fn goto(&mut self, next: Rc<Node>) {
+        self.prev = self.target.id;
+        self.target = next;
     }
-
-    fn into_node(self) -> Node {
-        self.into()
 }
 
-    fn children(&self) -> ChildIter {
-        ChildIter {
-            parent: Rc::clone(&self.target),
-            idx: 0,
-        }
-    }
+/// The Parser is responsible for turning a sequence of Tokens into a Parse Tree.
+pub struct Parser<'text> {
+    input: Lexer<'text>,
+    output: Cursor,
 }
 
-impl fmt::Debug for Tree {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
-        write!(f, "{:?}", self.target.borrow())
+impl<'text> Parser<'text> {
+    pub fn new(source: Lexer<'text>) -> Self {
+        Self {
+            input: source,
+            output: Node::new(),
         }
     }
 
-pub struct ChildIter {
-    /// pointer to the node in the tree whose children we are looking at.
-    parent: Rc<RefCell<Node>>,
-    idx: usize,
+    pub fn parse(mut self) -> Result<Cursor, ParseError> {
+        while self.step()? {}
+        self.output.up_to_root();
+        Ok(self.output)
     }
 
-impl Iterator for ChildIter {
-    type Item = Tree;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        if self.idx >= self.parent.borrow().children.len() {
-            None
-        } else {
-            let child = Rc::clone(&self.parent.borrow().children[self.idx]);
-            self.idx += 1;
-            Some(Tree{target: child})
-        }
+    fn step(&mut self) -> Result<bool, ParseError> {
+        match self.output.value() {
+            Value::Start => self.step_start(),
+            Value::Command => self.step_statement(),
+            Value::Terminal(_) => panic!(),
         }
     }
 
-impl From<Tree> for Node {
-    fn from(value: Tree) -> Self {
-        value.target.replace(Node::empty())
+    fn step_start(&mut self) -> Result<bool, ParseError> {
+        assert!(matches!(self.output.value(), Value::Start));
+        match self.input.peek()? {
+            Some(Token::Word(_)) => {
+                self.output.push(Value::Command)?;
+                let token = self.input.next().unwrap()?;
+                self.output.push(Value::Terminal(token))?;
+                self.output.up()?;
+                Ok(true)
             }
+            Some(Token::Glob(_)) => {
+                let token = self.input.next().unwrap()?;
+                Err(ParseError::UnexpectedToken(token))
             }
-
-impl From<Node> for Tree {
-    fn from(value: Node) -> Self {
-        Self {
-            target: Rc::new(RefCell::new(value)),
+            Some(Token::Semi(_)) => {
+                self.output.push(Value::Command)?;
+                let token = self.input.next().unwrap()?;
+                self.output.push(Value::Terminal(token))?;
+                self.output.up()?;
+                self.output.up()?;
+                Ok(true)
             }
+            Some(Token::Pipe(_)) => {
+                let token = self.input.next().unwrap()?;
+                Err(ParseError::UnexpectedToken(token))
+            }
+            None => Ok(false),
         }
     }
 
-// I don't know how to write a parser lol
-
-// ls
-//   Command{name: "ls"}
-
-// echo one two three
-//   Command{name: "echo", args: [Lit("one"), Lit("two"), Lit("three")]}
-
-// echo *.rs
-//   Command{name: "echo", args: [Glob("*.rs")]}
-//   Command{name: "echo", args: [Path("main.rs"), Path("parse.rs"), ...]}
-
-// cat main.rs | wc -l
-//   Pipe{
-//     src:  Command{name: "cat", args: [Lit("main.rs")]}
-//     dest: Command{name: "wc",  args: [Lit("-l")]}
-//   }
-
-// echo one ; echo two
-//   Sequence{
-//     children: [
-//       Command{Name:
-//     ]
-//   }
-
-pub fn parse<S: AsRef<str>>(text: S) -> Result<Tree, Error> {
-    let mut tree = Tree::new();
-    for token in lex(text)? {
-        match (tree.peek(), token) {
-            (Element::Empty, Token::Ident(cmd)) => {
-                tree = tree.push(Element::Command(cmd));
+    fn step_statement(&mut self) -> Result<bool, ParseError> {
+        assert!(matches!(self.output.value(), Value::Command));
+        match self.input.peek()? {
+            Some(Token::Word(_) | Token::Glob(_)) => {
+                let token = self.input.next().unwrap()?;
+                self.output.push(Value::Terminal(token))?;
+                self.output.up()?;
+                Ok(true)
             }
-            (Element::Command(_), Token::Ident(arg)) => {
-                tree = tree.append(Element::Literal(arg));
+            Some(Token::Pipe(_)) => {
+                todo!()
             }
-            _ => todo!(),
+            Some(Token::Semi(_)) => {
+                let token = self.input.next().unwrap()?;
+                self.output.push(Value::Terminal(token))?;
+                self.output.up()?;
+                self.output.up()?;
+                Ok(true)
             }
+            None => Ok(false),
         }
-    Ok(tree.root())
     }
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-    use Token::Pipe;
-
-    fn ident<S: Into<String>>(s: S) -> Token {
-        Token::Ident(s.into())
 }
 
-    macro_rules! lex {
-        (
-            $($name:ident: $line:literal $($token:expr)* ;)+
-        ) => {
-            $(
-            #[test]
-            fn $name() -> Result<(), Error> {
-                let mut tokens = lex($line)?;
+/*
 
-                $(
-                    assert!(tokens.len() > 0);
-                    let front = tokens.remove(0);
-                    assert_eq!($token, front);
-                )*
+a b
+  command
+    terminal
+      a
+    terminal
+      b
 
-                Ok(())
-            }
-            )*
-        };
-    }
+a | b
+  pipeline
+    command
+      terminal
+        a
+    terminal
+      |
+    command
+      terminal
+        b
 
-    lex! {
-    single_token:
-        "one"
-        ident("one");
 
-    two_tokens:
-        "ls one two"
-        ident("ls") ident("one") ident("two");
+*/
 
-    leading_whitespace:
-        "    one"
-        ident("one");
-
-    trailing_whitespace:
-        "one    "
-        ident("one");
-
-    surrounding_whitespace:
-        "  one    "
-        ident("one");
-
-    internal_hyphen:
-        "one-two"
-        ident("one-two");
-
-    pipe:
-        "|"
-        Pipe;
-
-    pipeline:
-        "one | two"
-        ident("one") Pipe ident("two");
-
-    pipeline_2:
-        "one |two"
-        ident("one") Pipe ident("two");
-    }
+#[cfg(test)]
+mod test {
+    use super::*;
+    use crate::lex::lex;
 
-    #[test]
-    fn empty_tree() {
-        let root = Tree::new().root();
-        assert!(root.is_root());
-        assert_eq!(root.peek(), Element::Empty);
-        assert_eq!(root.children().count(), 0);
+    fn parse(source: &str) -> Result<Cursor, ParseError> {
+        let tokens = Lexer::new(source);
+        let parser = Parser::new(tokens);
+        parser.parse()
     }
 
     #[test]
-    fn tree_root() {
-        let root = Tree::new()
-            .push(Element::Command(String::from("ls")))
-            .root();
-        assert!(root.is_root());
-        assert_eq!(root.children().count(), 0);
-        assert_eq!(root.into_node().elem, Element::Command(String::from("ls")));
+    fn root() {
+        let mut cursor = Node::new();
+        assert!(cursor.up().is_err());
+        assert!(cursor.target.value == Value::Start);
+        assert!(cursor.is_root());
     }
 
     #[test]
-    fn tree_push() {
-        let tree = Tree::new()
-            .push(Element::Command(String::from("ls")));
-        assert_eq!(tree.peek(), Element::Command(String::from("ls")));
-
-        let tree = Tree::new()
-            .push(Element::Command(String::from("ls")))
-            .append(Element::Command(String::from("one")));
-        assert_eq!(tree.peek(), Element::Command(String::from("ls")));
+    fn single_val() {
+        let mut cursor = Node::new();
+
+        let mut tokens = lex("  ls  ").unwrap();
+        let ls = tokens.pop().unwrap();
+        assert!(cursor.push(Value::Command).is_ok());
+        assert!(cursor.push(Value::Terminal(ls.clone())).is_ok());
+        assert!(cursor.push(Value::Terminal(ls.clone())).is_err());
+        assert!(cursor.target.value == Value::Terminal(ls));
+        assert!(!cursor.is_root());
+        assert!(cursor.up().is_ok());
+        assert!(cursor.up().is_ok());
+        assert!(cursor.is_root());
+        assert!(cursor.up().is_err());
+        assert!(cursor.value() == &Value::Start);
+        let root = cursor.into_root();
+        assert!(root.value == Value::Start);
     }
 
     #[test]
-    fn parse_args() {
-        let res = parse("ls one two three");
-        assert!(res.is_ok());
-
-        let tree = res.unwrap();
-        assert_eq!(tree.peek(), Element::Command(String::from("ls")));
-        assert_eq!(tree.children().count(), 3);
-
-        let mut args = tree.children();
-        assert_eq!(args.next().unwrap().peek(), Element::Literal(String::from("one")));
-        assert_eq!(args.next().unwrap().peek(), Element::Literal(String::from("two")));
-        assert_eq!(args.next().unwrap().peek(), Element::Literal(String::from("three")));
-        assert!(args.next().is_none());
+    fn test_parse() -> Result<(), ParseError> {
+        let x = parse("ls one two three")?;
+        println!("Parse tree: {x:?}");
+        // parse("*")?;
+        // parse("x* ls")?;
+        Ok(())
     }
 }

src/prompt.rs

@@ -1,7 +1,8 @@
 use crate::output;
-use std::io::Write;
 use anyhow::Result;
+use std::io::Write;
 
+/// draws the prompt that appears before a user enters a command
 pub struct Prompt {
     s: String,
 }
@@ -14,6 +15,11 @@ impl Prompt {
             //               |        |          +-------- clear styles
             //               |        |          |      +- show cursor
             //               v        v          v      v
+            #[cfg(debug_assertions)]
+            s: String::from("\x1b[?25l\x1b[31m ▷ \x1b[0m\x1b[?25h"),
+
+            #[allow(dead_code)]
+            #[cfg(not(debug_assertions))]
             s: String::from("\x1b[?25l\x1b[32m ▷ \x1b[0m\x1b[?25h"),
         }
     }
@@ -21,12 +27,13 @@ impl Prompt {
     pub fn print(&self, output: &mut output::Writer) -> Result<()> {
         match std::env::current_dir() {
             Ok(d) => {
-                let text = d.to_str().unwrap().to_owned() + &self.s;
-                output.write(text.as_bytes())?;
+                _ = write!(output, "{cwd}{arrow}", cwd = d.display(), arrow = self.s);
+                // let text = d.to_str().unwrap().to_owned() + &self.s;
+                // output.write(text.as_bytes())?;
             }
             Err(_) => {
-                output.write(self.s.as_bytes())?;
-            },
+                _ = write!(output, "{}", self.s);
+            }
         }
         Ok(())
     }

src/run.rs

@@ -0,0 +1,78 @@
+use crate::{builtin, error::ExecError, output};
+use std::{collections::HashMap, process};
+
+/// Eval represents anything that can be evaluated at runtime.
+pub trait Eval {
+    /// Evaluates the receiver, given the current runtime state.
+    fn eval(&self, ctx: &mut Context) -> Result<Value, ExecError>;
+}
+
+/// An individual value at runtime.
+#[derive(Debug, Clone)]
+pub enum Value {
+    /// The empty value. This is somewhat analagous to () in Rust or void in C or null in languages
+    /// that have null.
+    None,
+
+    /// A textual value.
+    Text(String),
+
+    /// The result of having executed some external OS process.
+    ExitStatus(process::ExitStatus),
+}
+
+impl Value {
+    pub fn try_to_string(self) -> Result<String, ExecError> {
+        Ok(self.try_as_str()?.to_string())
+    }
+
+    pub fn try_as_str(&self) -> Result<&str, ExecError> {
+        match self {
+            Value::None => Err(ExecError::type_error("expected text value, saw None value")),
+            Value::Text(v) => Ok(&v),
+            Value::ExitStatus(_) => Err(ExecError::type_error(
+                "expected text value, saw ExitStatus value",
+            )),
+        }
+    }
+}
+
+impl Eval for Value {
+    fn eval(&self, _: &mut Context) -> Result<Value, ExecError> {
+        Ok(self.clone())
+    }
+}
+
+/// The state of the runtime. In an environment-passing interpreter, this would be the environment.
+/// We avoid the term "environment" because in the context of an OS shell it's confusing whether it
+/// means the state of the interpreter itself, or the environment variables of the process. This
+/// State type represents the state of the interpreter itself.
+pub struct State {
+    #[allow(unused)]
+    variables: HashMap<&'static str, Value>,
+
+    pub(crate) builtins: HashMap<&'static str, builtin::Builtin>,
+}
+
+impl State {
+    pub fn new() -> Self {
+        Self {
+            variables: HashMap::new(),
+            builtins: builtin::all(),
+        }
+    }
+
+    pub fn builtin(&self, name: &str) -> Option<builtin::Builtin> {
+        self.builtins.get(name).copied()
+    }
+}
+
+pub trait Call {
+    fn call(&self, ctx: &mut Context, args: &[Value]) -> Result<Value, ExecError>;
+}
+
+pub struct Context<'s> {
+    pub(crate) stdout: output::Writer,
+    pub(crate) stderr: output::Writer,
+    pub(crate) state: &'s mut State,
+}

src/shell.rs

@@ -1,162 +0,0 @@
-use crate::{
-    ext::{Command, Echo, Printenv, Tail, Which},
-    input,
-    line::Line,
-    log::*,
-    output,
-    // parse::parse,
-    parse::{Element, Node},
-};
-
-use std::path::{Path, PathBuf};
-use std::rc::Rc;
-
-use anyhow::Result;
-use dirs;
-
-pub struct Shell {
-    pub input: input::Reader,
-    pub output: output::Writer,
-    pub line: Line,
-}
-
-impl Shell {
-    pub fn new() -> Result<Self> {
-        Ok(Self {
-            input: input::Reader::new()?,
-            output: output::Writer::stdout()?,
-            line: Line::new(),
-        })
-    }
-
-    pub fn back(&mut self, n: usize) -> Result<()> {
-        debug!("⛬ ←");
-        if self.line.back(n) {
-            self.output.back(n)?;
-        }
-        Ok(())
-    }
-
-    pub fn forward(&mut self, n: usize) -> Result<()> {
-        debug!("⛬ →");
-        if self.line.forward(n) {
-            self.output.forward(n)?;
-        }
-        Ok(())
-    }
-
-    pub fn reset(&mut self) -> Result<()> {
-        self.input.reset()?;
-        self.output.reset()?;
-        Ok(())
-    }
-
-    pub fn seek_right(&mut self) -> Result<()> {
-        info!("» seek right");
-        let n = self.line.seek_right();
-        if n > 0 {
-            // move right by the distance seeked
-            self.output.forward(n)?;
-        }
-        Ok(())
-    }
-
-    pub fn seek_left(&mut self) -> Result<()> {
-        info!("» seek left");
-        let n = self.line.seek_left();
-        if n > 0 {
-            // move left by the distance seeked
-            self.output.back(n)?;
-        }
-        Ok(())
-    }
-
-    pub fn expand_path<P: AsRef<Path>>(&self, p: P) -> PathBuf {
-        let p = p.as_ref();
-
-        match p.to_str() {
-            Some(s) => {
-                if s.len() == 0 || !s.starts_with('~') {
-                    return p.to_path_buf();
-                }
-            }
-            None => {
-                return p.to_path_buf();
-            }
-        }
-
-        let mut parts = p.components();
-        let first = parts.next().unwrap().as_os_str().to_str().unwrap();
-        if first == "~" {
-            dirs::home_dir().unwrap().join(parts)
-        } else {
-            let my_home = dirs::home_dir().unwrap();
-            let home_root = my_home.parent().unwrap();
-            let first = &first[1..];
-            let other_home = home_root.join(first);
-            other_home.join(parts)
-        }
-    }
-
-    pub fn exec(&mut self, root: Node) -> Result<bool> {
-        match root.elem {
-            Element::Empty => Ok(true),
-            Element::Command(cmd) => {
-                let args: Vec<String> = root
-                    .children
-                    .iter()
-                    .map(|node| match &node.borrow().elem {
-                        Element::Literal(v) => v.clone(),
-                        _ => todo!(),
-                    })
-                    .collect();
-                self.eval(
-                    cmd.to_string(),
-                    args.iter().map(|arg| arg.as_str()).collect(),
-                )
-            }
-            Element::Literal(_) => todo!(),
-        }
-    }
-
-    pub fn eval(&mut self, cmd: String, args: Vec<&str>) -> Result<bool> {
-        match cmd.as_str() {
-            "pwd" => {
-                let pb = std::env::current_dir()?;
-                println!("{}", pb.as_path().as_os_str().to_str().unwrap());
-                return Ok(true);
-            }
-            "cd" => {
-                let cwd = std::env::current_dir()?;
-                if args.len() > 0 {
-                    let target = cwd.join(args[0]);
-                    std::env::set_current_dir(target)?;
-                }
-                return Ok(true);
-            }
-            "printenv" => Printenv::create().exec(args),
-            "which" => Which::create().exec(args),
-            "tail" => Tail::create().exec(args),
-            "echo" => Echo::create().exec(args),
-            _ => {
-                let mut proc = std::process::Command::new(cmd);
-                if args.len() > 0 {
-                    proc.args(args);
-                }
-                match proc.spawn() {
-                    Ok(mut child) => {
-                        if let Err(e) = child.wait() {
-                            println!("error: {}", e);
-                            return Err(e.into());
-                        }
-                    }
-                    Err(e) => {
-                        println!("error: {}", e);
-                        return Ok(false);
-                    }
-                }
-                return Ok(true);
-            }
-        }
-    }
-}

src/syntax.rs

@@ -0,0 +1,252 @@
+use crate::{
+    builtin::Builtin,
+    error::{ExecError, ParseError},
+    lex::{Lexer, Token},
+    parse,
+    run::{Call, Context, Eval, Value},
+};
+use std::{collections::HashSet, env, ffi::OsString, process};
+
+/// The differnt types of nodes that may appear in our AST
+#[derive(Debug)]
+pub enum Element {
+    /// A Block is a list of statements
+    Block(Block),
+
+    /// A Command represents the desire to execute a command
+    Command(Command),
+
+    /// A literal is a ... literal value
+    Literal(Value),
+}
+
+impl Eval for Element {
+    fn eval(&self, ctx: &mut Context) -> Result<Value, ExecError> {
+        use Element::*;
+        match self {
+            Block(block) => block.eval(ctx),
+            Command(cmd) => cmd.eval(ctx),
+            Literal(v) => v.eval(ctx),
+        }
+    }
+}
+
+#[derive(Debug)]
+pub struct Block {
+    commands: Vec<Command>,
+}
+
+impl Block {
+    pub fn new() -> Self {
+        Block {
+            commands: Vec::new(),
+        }
+    }
+}
+
+impl Eval for Block {
+    fn eval(&self, ctx: &mut Context) -> Result<Value, ExecError> {
+        let mut v = Value::None;
+        for cmd in self.commands.iter() {
+            v = cmd.eval(ctx)?;
+        }
+        Ok(v)
+    }
+}
+
+#[derive(Debug)]
+pub struct Command {
+    name: Box<Element>,
+    args: Vec<Element>,
+}
+
+impl Command {
+    fn exec_builtin(&self, ctx: &mut Context, builtin: Builtin) -> Result<Value, ExecError> {
+        let args = self
+            .args
+            .iter()
+            .map(|elem| elem.eval(ctx))
+            .collect::<Result<Vec<_>, _>>()?;
+        builtin.call(ctx, &args)
+    }
+
+    fn exec_subprocess(&self, ctx: &mut Context, name: &str) -> Result<Value, ExecError> {
+        let args = self
+            .args
+            .iter()
+            .map(|elem| elem.eval(ctx)?.try_to_string())
+            .collect::<Result<Vec<_>, _>>()?;
+
+        let mut proc = process::Command::new(&name);
+        if args.len() > 0 {
+            proc.args(args);
+        }
+
+        let mut child = proc.spawn().map_err(|e| ExecError::ProcessSpawnError {
+            name: name.to_string(),
+            source: e,
+        })?;
+        let pid = child.id();
+        let status = child.wait().map_err(|e| ExecError::ProcessWaitError {
+            name: name.to_string(),
+            pid,
+            source: e,
+        })?;
+        Ok(Value::ExitStatus(status))
+    }
+}
+
+impl Eval for Command {
+    fn eval(&self, ctx: &mut Context) -> Result<Value, ExecError> {
+        let name = self.name.eval(ctx)?.try_to_string()?;
+        match ctx.state.builtin(&name) {
+            Some(builtin) => self.exec_builtin(ctx, builtin),
+            None => self.exec_subprocess(ctx, &name),
+        }
+    }
+}
+
+/// the TreeBuilder is responsible for converting a parse tree into an abstract syntax tree. This
+/// process leaves us with a tree that can be executed directly
+struct TreeBuilder {
+    visited: HashSet<usize>,
+}
+
+impl TreeBuilder {
+    fn new() -> Self {
+        Self {
+            visited: HashSet::new(),
+        }
+    }
+
+    fn parse(&mut self, source: &mut parse::Cursor) -> Result<Element, ParseError> {
+        let e = match source.value() {
+            parse::Value::Start => {
+                let mut root = Block::new();
+                let children = source.iter_children();
+                for mut child in children {
+                    if child.target.is_semi() {
+                        continue;
+                    }
+                    let e = self.parse(&mut child)?;
+                    match e {
+                        Element::Command(cmd) => root.commands.push(cmd),
+                        _ => panic!(),
+                    }
+                }
+                Element::Block(root)
+            }
+            parse::Value::Command => {
+                let mut children = source.iter_children();
+                let mut first = match children.next() {
+                    Some(child) => child,
+                    None => return Err(ParseError::StatementIsEmpty),
+                };
+                if first.target.is_semi() {
+                    return Err(ParseError::StatementIsEmpty);
+                }
+                let name = self.parse(&mut first)?;
+                let mut cmd = Command {
+                    name: Box::new(name),
+                    args: Vec::new(),
+                };
+
+                // we set complete to true when we find a semicolon. If there are any parse nodes
+                // that appear -after- a semicolon, that indicates a bug in the prior stage.
+                let mut complete = false;
+                for mut child in children {
+                    if child.target.is_semi() {
+                        complete = true;
+                        continue;
+                    }
+
+                    if complete {
+                        return Err(ParseError::DanglingElements);
+                    } else {
+                        let e = self.parse(&mut child)?;
+                        cmd.args.push(e);
+                    }
+                }
+                Element::Command(cmd)
+            }
+            parse::Value::Terminal(Token::Word(word)) => {
+                let text = word.to_string();
+                let text = expand(&text)?;
+                Element::Literal(Value::Text(text))
+            }
+            parse::Value::Terminal(Token::Glob(_)) => {
+                todo!()
+            }
+            parse::Value::Terminal(Token::Pipe(_)) => {
+                todo!()
+            }
+            parse::Value::Terminal(Token::Semi(_)) => {
+                return Err(ParseError::WhyParseSemicolon);
+            }
+        };
+        self.visited.insert(source.target.id);
+        Ok(e)
+    }
+}
+
+pub fn parse(source: &str) -> Result<Element, ParseError> {
+    let tokens = Lexer::new(source);
+    let parser = parse::Parser::new(tokens);
+    let mut parse_tree = parser.parse()?;
+    let mut builder = TreeBuilder::new();
+    let root = builder.parse(&mut parse_tree)?;
+    Ok(root)
+}
+
+#[cfg(target_os = "windows")]
+fn home_dir() -> Result<OsString, ExpandError> {
+    env::var_os("HOMEPATH").ok_or(ExpandError::EmptyEnvironmentVar(String::from("HOMEPATH")))
+}
+
+#[derive(thiserror::Error, Debug)]
+pub enum ExpandError {
+    #[error("environment var is not set: {0}")]
+    EmptyEnvironmentVar(String),
+
+    #[error("home dir is not utf-8")]
+    NotUnicode,
+}
+
+fn expand(text: &str) -> Result<String, ExpandError> {
+    let chars = text.chars();
+    // let mut escape = false;
+    let mut s = String::new();
+    for c in chars {
+        // if !escape && c == '\\' {
+        //     escape = true;
+        //     continue;
+        // }
+
+        // if escape {
+        //     s.push(c);
+        //     escape = false;
+        //     continue;
+        // }
+
+        if c == '~' {
+            let p = home_dir()?;
+            s.push_str(p.to_str().ok_or(ExpandError::NotUnicode)?);
+            continue;
+        }
+
+        s.push(c);
+    }
+    Ok(s)
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn hi() -> Result<(), ParseError> {
+        let e = parse("ls one two three")?;
+        print!("{:?}", e);
+        Ok(())
+    }
+}

src/topo.rs

@@ -0,0 +1,207 @@
+use crate::error::LexError;
+use std::{collections::VecDeque, fmt, ops::Range, str::Chars};
+
+/// A position a some two dimensional space defined by lines and columns, specifically concerned
+/// with positions of characters within text
+#[derive(PartialEq, Clone, Copy)]
+pub struct Position {
+    /// The visual line in which this glyph appears in the source text
+    pub line: u64,
+
+    /// The visual column in which this glyph appears in the source text
+    pub column: u64,
+}
+
+impl Position {
+    /// The 0,0 position: the very first character of a document is at the 0,0 position
+    pub fn origin() -> Self {
+        Self { line: 0, column: 0 }
+    }
+
+    /// Increments position by column, going from the current line,column position to the next
+    /// column on the same line.
+    pub fn incr(&mut self) -> Position {
+        let p = *self;
+        self.column += 1;
+        p
+    }
+
+    /// Increments the position by line, going from the current line,column position to the
+    /// beginning of the next line.
+    pub fn incr_line(&mut self) -> Position {
+        let p = *self;
+        self.column = 0;
+        self.line += 1;
+        p
+    }
+}
+
+impl fmt::Debug for Position {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
+        write!(
+            f,
+            "({line}, {column})",
+            line = self.line,
+            column = self.column
+        )
+    }
+}
+
+impl fmt::Display for Position {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
+        (self as &dyn fmt::Debug).fmt(f)
+    }
+}
+
+/// A Glyph represents a character occurring at some specific position in some input text.
+#[derive(PartialEq, Clone)]
+pub struct Glyph {
+    /// the unicode code point of the glyph
+    pub glyph: char,
+
+    /// The visual position in which the glyph appears; i.e., the human-comprehensible location
+    /// of the glyph in the source text
+    pub position: Position,
+
+    /// The byte offsets corresponding to this topoglyph in the source data; i.e., the
+    /// machine-comprehensible location of the glyph in the source text
+    pub bytes: Range<u64>,
+}
+
+impl Glyph {
+    /// checks to see whether or not the character for this glyph is a word character
+    pub fn is_word(&self) -> bool {
+        match self.glyph {
+            '-' | '/' | '\\' | '.' | ':' | '~' => true,
+            _ => self.glyph.is_alphanumeric(),
+        }
+    }
+
+    /// checks to see whether or not the character for this glyph is a glob character
+    pub fn is_glob(&self) -> bool {
+        self.is_word() || self.glyph == '*'
+    }
+}
+
+impl fmt::Debug for Glyph {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
+        write!(
+            f,
+            "[{char} ({pos:?})]",
+            char = self.glyph,
+            pos = self.position
+        )
+    }
+}
+/// Glyphs produces [glyphs](Glyph) for a source text; i.e., it is an iterator of [Glyph] values.
+/// Glyphs is used to control reading from the source text and keeps a lookahead buffer of glyphs
+/// that have not been processed. While a [crate::lex::Lexer] is responsible for the creation and
+/// iteration of [tokens](crate::lex::Token), Glyphs is responsible for the creation and iteration
+/// of glyphs.
+pub struct Glyphs<'text> {
+    /// the characters of the input text that we're interested in reading
+    source: Chars<'text>,
+
+    /// the position of the next character in the source text
+    pub(crate) next_position: Position,
+
+    /// the number of bytes we've read from our input document so far
+    bytes_read: u64,
+
+    /// lookahead buffer
+    lookahead: VecDeque<Glyph>,
+}
+
+impl<'text> Glyphs<'text> {
+    pub fn new(source: &'text str) -> Self {
+        // neat
+        Self {
+            source: source.chars(),
+            next_position: Position::origin(),
+            bytes_read: 0,
+            lookahead: VecDeque::new(),
+        }
+    }
+
+    /// reads the next n characters from the source text into our lookahead buffer
+    fn fill_lookahead(&mut self, n: usize) -> bool {
+        while self.lookahead.len() < n {
+            let c = match self.source.next() {
+                Some(c) => c,
+                None => break,
+            };
+
+            let len = c.len_utf8();
+            let start = self.bytes_read;
+            self.bytes_read += len as u64;
+            let position = if c == '\n' {
+                self.next_position.incr_line()
+            } else {
+                self.next_position.incr()
+            };
+            self.lookahead.push_back(Glyph {
+                glyph: c,
+                position,
+                bytes: Range {
+                    start,
+                    end: self.bytes_read,
+                },
+            })
+        }
+        self.lookahead.len() == n
+    }
+
+    /// returns a reference to the next character from the source text, advancing our internal
+    /// lookahead buffer if necessary. Returns None if we're already at the end of our source text.
+    pub fn peek(&mut self) -> Option<&Glyph> {
+        self.peek_at(0)
+    }
+
+    /// takes the next character from our input text
+    pub fn pop(&mut self) -> Result<Glyph, LexError> {
+        self.next()
+            .ok_or(LexError::UnexpectedEOF(self.next_position))
+    }
+
+    /// returns a reference to a character in our lookahead buffer at a given position. This allows
+    /// us to perform a lookahead read without consuming any tokens, maintaining our current
+    /// position and keeping our unconsumed characters safe.
+    fn peek_at(&mut self, idx: usize) -> Option<&Glyph> {
+        self.fill_lookahead(idx + 1);
+        self.lookahead.get(idx)
+    }
+
+    /// discards characters from our current position so long as the upcoming characters match some
+    /// predicate. This is called yeet_while instead of skip_while in order to avoid conflicting
+    /// with the
+    /// [skip_while](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.skip_while)
+    /// method of the stdlib Iterator trait.
+    pub fn yeet_while<F>(&mut self, mut pred: F)
+    where
+        F: FnMut(&Glyph) -> bool,
+    {
+        while let Some(g) = self.peek() {
+            if pred(&g) {
+                self.next();
+            } else {
+                return;
+            }
+        }
+    }
+
+    /// discards all of the upcoming whitespace characters. After calling yeet_whitespace, the next
+    /// Glyp is guaranteed to be either non-whitespace or None (None would be because we've hit
+    /// EOF)
+    pub fn yeet_whitespace(&mut self) {
+        self.yeet_while(|tg| tg.glyph.is_whitespace());
+    }
+}
+
+impl<'text> Iterator for Glyphs<'text> {
+    type Item = Glyph;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.fill_lookahead(1);
+        self.lookahead.pop_front()
+    }
+}