diff --git a/environments.js b/environments.js
index 44558fc..d88426e 100644
--- a/environments.js
+++ b/environments.js
@@ -3,13 +3,14 @@
  * with a few built-in (a standard Prelude environment)
  */
 
-// returns the new environment after mutating it
-// values = [(identifier, JLambda expression)]
-
 var errors = require("./errors.js");
 var rep = require("./representation.js");
 
 
+/*
+ * returns the new environment after mutating it
+ * values = [(identifier, JLambda expression)]
+ */
 function extend(env, values) {
   var new_env = {};
   var env_keys = Object.keys(env);
diff --git a/free_vars.js b/free_vars.js
index da87a60..602c31d 100644
--- a/free_vars.js
+++ b/free_vars.js
@@ -1,4 +1,4 @@
-/* Takes an AST and converts all of the functions into closures.
+/* Takes an AST and converts all of the functions into "closures"
  * A closure is a triple of:
  *  the bound variables in a function or let
  *  the free variables in a function or let
@@ -19,10 +19,8 @@
  */
 
 var rep = require("./representation.js");
-var env = require("./environments.js");
 var errors = require("./errors.js");
 var parser = require("./parse.js");
-var pprint = require("./pprint.js");
 var $ = require("./tools.js");
 var _ = require("underscore");
 
@@ -106,6 +104,9 @@ function annotate_fvs(stx) {
   return new rep.Closure(bound_vars, free_variables, stx, []);
 }
 
+/*
+ * This traverse the tree and gathers up all of the free variables of various functions/let bindings
+ */
 function annotate_fvs_all(stx) {
   var closure;
   switch (stx.exprType) {
diff --git a/parse.js b/parse.js
index fa25ccb..2c4e23a 100755
--- a/parse.js
+++ b/parse.js
@@ -367,12 +367,17 @@ function parseDataType(tokens, linenum, charnum) {
                              typeName.charnum,
                              "Expected a type operator in data type definition");
   }
-  parameters = parseMany(parse,
+  if (fst(tokens)[0] !== "right_paren") {
+    parameters = parseMany(parse,
                          validName,
                          validFormPar,
                          tokens,
                          charnum,
                          linenum);
+  }
+  else {
+    parameters = [];
+  }
   if (!tokens || (fst(tokens)[0]) !== "right_paren") {
     throw error.JSyntaxError(_.last(parameters).linenum,
                              _.last(parameters).charnum,
@@ -402,7 +407,7 @@ function parseDefType(tokens, linenum, charnum) {
   }
   if (fst(tokens)[0] === "left_paren") {
     /* It's an actual data type definition
-     * i.e. not just a newtype
+     * i.e. not just an alias
      */
     tokens.pop();
     return parseDataType(tokens, linenum, charnum);
@@ -424,7 +429,7 @@ function parseDefType(tokens, linenum, charnum) {
     if (lhs.exprType !== "TypeOperator") {
       throw error.JSyntaxError(lhs.linenum,
                                lhs.charnum,
-                               "left-hand side of type definition was not a type operator");
+                               "left-hand side of type alias was not a type operator");
     }
     rhs = parse(tokens, linenum, charnum);
 
@@ -432,7 +437,7 @@ function parseDefType(tokens, linenum, charnum) {
         rhs.exprType !== "TypeOperator") {
       throw error.JSyntaxError(rhs.linenum,
                                rhs.charnum,
-                               "was expecting an application or type operator on the right-hand side of a type definition");
+                               "was expecting an application or type operator on the right-hand side of a type alias");
     }
     result = addSrcPos(new typ.DefType(lhs, rhs), tokens, rhs.linenum, rhs.charnum);
     return result;
diff --git a/prelude.jl b/prelude.jl
index 3fa12cc..1ed259f 100644
--- a/prelude.jl
+++ b/prelude.jl
@@ -4,24 +4,29 @@
 
 
 ;; Type definitions
-deftype String (A300 Char)
+deftype String (Vector Char)
 
-deftype Int Intrinsic
+deftype (Int) Intrinsic
 
-deftype Float Intrinsic
+deftype (Float) Intrinsic
 
-deftype Char Intrinsic
+deftype (Char) Intrinsic
 
-deftype Byte Intrinsic
+deftype (Byte) Intrinsic
 
-deftype Void Intrinsic
+deftype (Void) Intrinsic
 
-deftype IO Intrinsic
+deftype (IO a) Intrinsic
+
+deftype (Vector a) Intrinsic
 
 deftype (List a)
   (Empty |
    (Cons a (List a)))
 
+deftype (Bottom)
+  Undefined
+
 deftype (Maybe a)
   (Nothing |
    (Just a))
diff --git a/representation.js b/representation.js
index 0a80723..39c3543 100644
--- a/representation.js
+++ b/representation.js
@@ -368,28 +368,11 @@ function makeGensym() {
 
 var gensym = makeGensym();
 
-//console.log(isTypeExpr(new Name("T")));
-
 OPInfo = {
-         /*"+" : [3, "Left"],
-         "-" :  [3, "Left"],
-         "*" :  [4, "Left"],
-         "/" :  [4, "Left"],
-         "^" :  [5, "Right"]
-          "++" : [3, "Left"],
-          "==" : [2, "Left"],
-          ">" :  [2, "Left"],
-          ">=" : [2, "Left"],
-          "<" :  [2, "Left"],
-          "<=" : [2, "Left"],
-          "&&" : [2, "Left"],
-          "||" : [2, "Left"],*/
           "::" : [2, "Left"],
-          /*":" : [1, "Left"],
-          "$" : [1, "Left"],
-          "." : [1, "Left"],*/
           "," : [1, "Left"],
-          "->" : [1, "Right"]};
+          "->" : [1, "Right"]
+         };
 
 module.exports =
    {
diff --git a/typecheck.js b/typecheck.js
index 7c198c6..e105e94 100644
--- a/typecheck.js
+++ b/typecheck.js
@@ -13,7 +13,7 @@
 var rep = require("./representation.js");
 var env = require("./environments.js");
 
-var TypeOp = rep.TypeOp;
-var TypeVar = rep.TypeVar;
-
-
+/*
+ * Map all bindings with explicit type annotations in the environment
+ */
+function gather_annotations(stx) {