fix bug with validity checking of type definitions

example.jl

@@ -1,6 +1,9 @@
 defop 2 Left (a ++ b)
  (a - b)
 
+
+def foo# 3
+
 deftype Foo (A -> B)
 
 ;; here is a comment

prelude.jl

@@ -2,11 +2,9 @@
 ;; It is sort of special in that it doesn't care whether there are any associated definitions
 ;; just that there are type definitions for that particular binding's name
 
-deftype String (List Char)
 
-deftype (List a)
+;; Type definitions
-  (Empty |
+deftype String (A300 Char)
-   (Cons a (List a)))
 
 deftype Int Intrinsic
 
@@ -18,6 +16,22 @@ deftype Byte Intrinsic
 
 deftype Void Intrinsic
 
+deftype IO Intrinsic
+
+deftype (List a)
+  (Empty |
+   (Cons a (List a)))
+
+deftype (Maybe a)
+  (Nothing |
+   (Just a))
+
+deftype (Either a b)
+  ((Left a) |
+   (Right b))
+
+;; List functions
+
 (: :: (a -> (List a) -> (List a)))
 
 (map :: ((a -> b) -> (List a) -> (List b)))
@@ -28,4 +42,16 @@ deftype Void Intrinsic
 
 (!! :: (Int -> (List a) -> a))
 
+(take :: (Int -> (List a) -> (Maybe (List a))))
+
+(drop :: (Int -> (List a) -> (Maybe (List a))))
+
+;; Optional functions
+
+(maybe :: (b -> (a -> b) -> (Maybe a) -> b))
+
+(either :: ((b -> c) -> (b -> c) -> (Either a b) -> c))
+
+;; I/O functions
+
 (print :: (String -> (IO Void)))

representation.js

@@ -278,7 +278,7 @@ function TypeDecl(expression, type) {
       "Left-hand-side of type declaration must not be in the type language"
       );
   }
-  if (!isTypeExprRec(type)) {
+  if (isTypeExprRec(type).failed) {
     throw errors.JInternalError(
       "Right-hand-side of type declaration must be a type expression"
       );
@@ -295,7 +295,7 @@ function DefType(lhs, rhs) {
   /* Both rhs and lhs are expected
    * to be fully desugared already
    */
-  if (!isTypeExprRec(rhs) ||
+  if (isTypeExprRec(rhs).failed ||
       !isTypeExpr(lhs)) {
         throw errors.JSyntaxError(
           rhs.linenum,
@@ -331,7 +331,7 @@ function DataType(name, params, type) {
       "which is a type operator");
   }
   _.each(params, checkName);
-  if (!isTypeExprRec(type)) {
+  if (isTypeExprRec(type).failed) {
     throw errors.JSyntaxError(
       type.linenum,
       type.charnum,