add doc.get and get subcommand

cmd/moon/main.go

@@ -54,6 +54,19 @@ func to_json(n int) {
 	os.Stdout.Write(b)
 }
 
+func get() {
+	docpath := flag.Arg(1)
+	doc, err := moon.Read(input(2))
+	if err != nil {
+		bail(1, "input error: %s", err)
+	}
+	var v interface{}
+	if err := doc.Get(docpath, &v); err != nil {
+		bail(1, "error reading value at path %s: %s", docpath, err)
+	}
+	fmt.Println(v)
+}
+
 func bail(status int, t string, args ...interface{}) {
 	var w io.Writer
 	if status == 0 {
@@ -72,8 +85,10 @@ func main() {
 		check()
 	case "to":
 		to()
+	case "get":
+		get()
 	case "":
-		bail(1, "must specify an action.\nvalid actions: check lex parse to")
+		bail(1, "must specify an action.\nvalid actions: check to get")
 	default:
 		bail(1, "no such action:%s", flag.Arg(0))
 	}

lib/doc.go

@@ -2,6 +2,8 @@ package moon
 
 import (
 	"encoding/json"
+	"fmt"
+	"reflect"
 )
 
 type Doc struct {
@@ -11,3 +13,24 @@ type Doc struct {
 func (d *Doc) MarshalJSON() ([]byte, error) {
 	return json.Marshal(d.items)
 }
+
+func (d *Doc) Get(path string, dest interface{}) error {
+	if d.items == nil {
+		return fmt.Errorf("no item found at path %s (doc is empty)", path)
+	}
+
+	v, ok := d.items[path]
+	if !ok {
+		return fmt.Errorf("no item found at path %s", path)
+	}
+
+	dt := reflect.TypeOf(dest)
+	if dt.Kind() != reflect.Ptr {
+		return fmt.Errorf("destination is of type %v; a pointer type is required", dt)
+	}
+
+	dv := reflect.ValueOf(dest)
+	dve := dv.Elem()
+	dve.Set(reflect.ValueOf(v))
+	return nil
+}

lib/doc_test.go

@@ -0,0 +1,23 @@
+package moon
+
+import (
+	"testing"
+)
+
+func TestDoc(t *testing.T) {
+	doc, err := ReadString(`
+    name: "jordan"
+    `)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	var name string
+	if err := doc.Get("name", &name); err != nil {
+		t.Error(err)
+		return
+	}
+	if name != "jordan" {
+		t.Errorf("unexpected name value, expected 'jordan', saw '%s'", name)
+	}
+}

lib/parse.go

@@ -1,6 +1,7 @@
 package moon
 
 import (
+	"bytes"
 	"fmt"
 	"io"
 	"strings"
@@ -8,6 +9,10 @@ import (
 
 const ()
 
+// Reads a moon document from a given io.Reader. The io.Reader is advanced to
+// EOF. The reader is not closed after reading, since it's an io.Reader and not
+// an io.ReadCloser. In the event of error, the state that the source reader
+// will be left in is undefined.
 func Read(r io.Reader) (*Doc, error) {
 	tree, err := parse(r)
 	if err != nil {
@@ -25,6 +30,18 @@ func Read(r io.Reader) (*Doc, error) {
 	return &Doc{items: ctx}, nil
 }
 
+// Reads a moon document from a string. This is purely a convenience method;
+// all it does is create a buffer and call the moon.Read function.
+func ReadString(source string) (*Doc, error) {
+	return Read(strings.NewReader(source))
+}
+
+// Reads a moon document from a slice of bytes. This is purely a concenience
+// method; like ReadString, it simply creates a buffer and calls moon.Read
+func ReadBytes(b []byte) (*Doc, error) {
+	return Read(bytes.NewBuffer(b))
+}
+
 func parse(r io.Reader) (node, error) {
 	p := &parser{
 		root:   newRootNode(),