pretty print debugging for data type defs, fixed another mistake

parse.js

@@ -377,7 +377,7 @@ function parseDataType(tokens, linenum, charnum) {
   }
   tokens.pop();
   typeBody = parse(tokens);
-  result = addSrcPos(new typ.DataType(parameters, typeBody), tokens, typeBody.linenum, typeBody.charnum);
+  result = addSrcPos(new typ.DataType(typeName, parameters, typeBody), tokens, typeBody.linenum, typeBody.charnum);
 
   return result;
 }

pprint.js

@@ -30,6 +30,10 @@ function pprintDefType(stx) {
   return pprint(stx.lhs) + " = " + pprint(stx.rhs);
 }
 
+function pprintTypeFunc(stx) {
+  return "(" + stx.name.name + " " + stx.params.map(pprint).join(" ") + ") = " + pprint(stx.type);
+}
+
 function pprint(expr) {
   if (expr.exprType === "Name") {
     return expr.val;
@@ -63,6 +67,9 @@ function pprint(expr) {
   else if (expr.exprType === "TypeDefinition") {
     return pprintDefType(expr);
   }
+  else if (expr.exprType === "TypeFuncDefinition") {
+    return pprintTypeFunc(expr);
+  }
   else if (expr.exprType === "If") {
     return pprintIf(expr);
   }

representation.js

@@ -319,10 +319,17 @@ function checkName(exp) {
   }
 }
 
-function DataType(params, type) {
+function DataType(name, params, type) {
   /* Params is a list of type variables
    * type is a type expression
    */
+  if (name.exprType !== "TypeOperator") {
+    throw errors.JSyntaxError(
+      name.linenum,
+      name.charnum,
+      "First element in a data type definition must be its name " +
+      "which is a type operator");
+  }
   _.each(params, checkName);
   if (!isTypeExprRec(type)) {
     throw errors.JSyntaxError(
@@ -330,6 +337,7 @@ function DataType(params, type) {
       type.charnum,
       "Body of a type definition must be a valid type expression");
   }
+  this.name = name;
   this.params = params;
   this.type = type;
   this.exprType = "TypeFuncDefinition";