hey look, variables

ex.moon

@@ -32,6 +32,5 @@ other_hash: {
 
 item_one: "this is item one"
 
-# we should be able to reference variables defined earlier
-# (this doesn't work yet)
-# item_two: item_one
+# we may reference an item that was defined earlier
+item_two: item_one

node.go

@@ -21,6 +21,7 @@ const (
 	n_number
 	n_list
 	n_object
+	n_variable
 )
 
 var indent = "  "
@@ -410,3 +411,32 @@ func (o *objectNode) eval(ctx map[string]interface{}) (interface{}, error) {
 	}
 	return out, nil
 }
+
+type variableNode string
+
+func (v *variableNode) Type() nodeType {
+	return n_variable
+}
+
+func (v *variableNode) parse(p *parser) error {
+	t := p.next()
+	if t.t != t_name {
+		return fmt.Errorf("unexpected %s token when parsing variable", t.t)
+	}
+	*v = variableNode(t.s)
+	return nil
+}
+
+func (v *variableNode) pretty(w io.Writer, prefix string) error {
+	fmt.Fprintf(w, "%svariable:\n", prefix)
+	fmt.Fprintf(w, "%s%s\n", prefix+indent, string(*v))
+	return nil
+}
+
+func (v *variableNode) eval(ctx map[string]interface{}) (interface{}, error) {
+	value, ok := ctx[string(*v)]
+	if !ok {
+		return nil, fmt.Errorf("undefined variable: %s", *v)
+	}
+	return value, nil
+}

parse.go

@@ -106,6 +106,12 @@ func (p *parser) parseValue() (node, error) {
 				return nil, err
 			}
 			return n, nil
+		case t_name:
+			n := new(variableNode)
+			if err := n.parse(p); err != nil {
+				return nil, err
+			}
+			return n, nil
 		default:
 			return nil, fmt.Errorf("parse error: unexpected %v token while looking for value", t.t)
 		}

tests/parse/05.in

@@ -0,0 +1,2 @@
+an_item: "this is the value of the item"
+a_variable: an_item

tests/parse/05.out

@@ -0,0 +1,13 @@
+root:
+  assign:
+    name:
+      an_item
+    value:
+      string:
+        this is the value of the item
+  assign:
+    name:
+      a_variable
+    value:
+      variable:
+        an_item