diff --git a/tokenize.js b/tokenize.js
index b03a87d..ccc8dce 100755
--- a/tokenize.js
+++ b/tokenize.js
@@ -10,6 +10,9 @@ function isDigit(a) {
   if (!a)
     return false;
   var code = a.charCodeAt();
+  if (isNaN(code)) {
+    return false;
+  }
   return (46 < code &&
           code < 58 ||
           code < 58 &&
@@ -21,6 +24,9 @@ function isWhitespace(a) {
     return true;
 
   var code = a.charCodeAt();
+  if (isNaN(code)) {
+    return false;
+  }
   return (code === 9 ||
           code === 32 ||
           code === 10 ||
@@ -30,7 +36,8 @@ function isWhitespace(a) {
 
 function isIdentifier(a) {
   var code = a.charCodeAt();
-  return (code !== 41 &&
+  return (!isNaN(code) &&
+          code !== 41 &&
           code !== 40 &&
           code !== 125 &&
           code !== 123 &&
diff --git a/treegen.js b/treegen.js
index 142f0b9..f85a2aa 100644
--- a/treegen.js
+++ b/treegen.js
@@ -10,10 +10,11 @@ var qc = require("quickcheck");
 function arbIdentifier() {
     var st = qc.arbString()
     if (lex.isIdentifier(st)) {
-      return st;
+      return new repr.Name(st);
     }
     else {
       return arbIdentifier();
     }
 }
 
+console.log(arbIdentifier());