diff --git a/main.go b/main.go
index 850c98b..794a9c1 100644
--- a/main.go
+++ b/main.go
@@ -1,37 +1,37 @@
 package main
 
 import (
+	"encoding/json"
 	"flag"
 	"fmt"
 	"io"
 	"os"
 )
 
-func input() io.ReadCloser {
-	if flag.Arg(1) == "" {
+func input(n int) io.ReadCloser {
+	if flag.Arg(n) == "" {
 		return os.Stdin
 	} else {
-		f, err := os.Open(flag.Arg(1))
+		f, err := os.Open(flag.Arg(n))
 		if err != nil {
-			fmt.Fprintf(os.Stderr, "error: %s\n", err)
-			os.Exit(1)
+			bail(1, "input error: %s", err)
 		}
 		return f
 	}
 }
 
 func check() {
-	r := input()
+	r := input(1)
 	defer r.Close()
 
 	_, err := parse(r)
 	if err != nil {
-		fmt.Fprintf(os.Stderr, "%s\n", err)
+		bail(1, "parse error: %s", err)
 	}
 }
 
 func lexx() {
-	r := input()
+	r := input(1)
 	defer r.Close()
 
 	c := lex(r)
@@ -41,20 +41,65 @@ func lexx() {
 }
 
 func parsse() {
-	r := input()
+	r := input(1)
 	defer r.Close()
 
 	n, err := parse(r)
 	if err != nil {
-		fmt.Fprintf(os.Stderr, "error: %s\n", err)
-		os.Exit(1)
+		bail(1, "parse error: %s", err)
 	}
 	if err := n.pretty(os.Stdout, ""); err != nil {
-		fmt.Fprintf(os.Stderr, "error: %s\n", err)
+		bail(1, "output error: %s", err)
+	}
+}
+
+func eval(r io.Reader) (map[string]interface{}, error) {
+	n, err := parse(r)
+	if err != nil {
+		return nil, fmt.Errorf("parse error: %s\n", err)
+	}
+
+	ctx := make(map[string]interface{})
+	if err := n.eval(ctx); err != nil {
+		return nil, fmt.Errorf("eval error: %s\n", err)
+	}
+	return ctx, nil
+}
+
+func to() {
+	switch flag.Arg(1) {
+	case "json":
+		to_json(2)
+	default:
+		fmt.Fprintf(os.Stderr, "%s is not a valid output format\n", flag.Arg(1))
+		fmt.Fprintln(os.Stderr, "valid output formats: json")
 		os.Exit(1)
 	}
 }
 
+func to_json(n int) {
+	v, err := eval(input(n))
+	if err != nil {
+		bail(1, "input error: %s", err)
+	}
+	b, err := json.MarshalIndent(v, "", "    ")
+	if err != nil {
+		bail(1, "encode error: %s", err)
+	}
+	os.Stdout.Write(b)
+}
+
+func bail(status int, t string, args ...interface{}) {
+	var w io.Writer
+	if status == 0 {
+		w = os.Stdout
+	} else {
+		w = os.Stderr
+	}
+	fmt.Fprintf(w, t+"\n", args...)
+	os.Exit(status)
+}
+
 func main() {
 	flag.Parse()
 	switch flag.Arg(0) {
@@ -64,11 +109,11 @@ func main() {
 		lexx()
 	case "parse":
 		parsse()
+	case "to":
+		to()
 	case "":
-		fmt.Fprintf(os.Stderr, "specify an action (check)\n")
-		os.Exit(1)
+		bail(1, "must specify an action.\nvalid actions: check lex parse to")
 	default:
-		fmt.Fprintf(os.Stderr, "no such action: %s\n", flag.Arg(0))
-		os.Exit(1)
+		bail(1, "no such action:%s", flag.Arg(0))
 	}
 }
diff --git a/node.go b/node.go
index 06b5170..204fa17 100644
--- a/node.go
+++ b/node.go
@@ -23,6 +23,7 @@ type node interface {
 	Type() nodeType
 	parse(*parser) error
 	pretty(io.Writer, string) error
+	eval(map[string]interface{}) error
 }
 
 type rootNode struct {
@@ -90,6 +91,15 @@ func (n *rootNode) pretty(w io.Writer, prefix string) error {
 	return nil
 }
 
+func (n *rootNode) eval(ctx map[string]interface{}) error {
+	for _, child := range n.children {
+		if err := child.eval(ctx); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
 type commentNode struct {
 	body string
 }
@@ -126,6 +136,10 @@ func (n *commentNode) pretty(w io.Writer, prefix string) error {
 	return nil
 }
 
+func (n *commentNode) eval(ctx map[string]interface{}) error {
+	return nil
+}
+
 type assignmentNode struct {
 	name  string
 	value interface{}
@@ -167,5 +181,13 @@ func (n *assignmentNode) pretty(w io.Writer, prefix string) error {
 	return nil
 }
 
+func (n *assignmentNode) eval(ctx map[string]interface{}) error {
+	if _, ok := ctx[n.name]; ok {
+		return fmt.Errorf("invalid re-declaration: %s", n.name)
+	}
+	ctx[n.name] = n.value
+	return nil
+}
+
 type list []interface{}
 type object map[string]interface{}