wrote more of the compressor and added some tests

lib/ast.js

@@ -2,6 +2,7 @@ function DEFNODE(type, props, methods, base) {
     if (arguments.length < 4) base = AST_Node;
     if (!props) props = [];
     else props = props.split(/\s+/);
+    var self_props = props;
     if (base && base.PROPS)
         props = props.concat(base.PROPS);
     var code = "return function AST_" + type + "(props){ if (props) { ";
@@ -19,6 +20,7 @@ function DEFNODE(type, props, methods, base) {
     }
     ctor.prototype.CTOR = ctor;
     ctor.PROPS = props || null;
+    ctor.SELF_PROPS = self_props;
     if (type) {
         ctor.prototype.TYPE = ctor.TYPE = type;
     }
@@ -563,7 +565,10 @@ TreeWalker.prototype = {
         if (!ret && descend) {
             descend.call(node);
         }
-        this.stack.pop(node);
+        this.stack.pop();
         return ret;
+    },
+    parent: function(n) {
+        return this.stack[this.stack.length - 2 - (n || 0)];
     }
 };