interactive prompt can handle polymorphic types

structures/types.js

@@ -13,17 +13,8 @@ export const fnType = makeTypeConstructor(symbolFunction)(2);
 
 export const isFunction = type => getSymbol(type) === symbolFunction;
 
-// Convenience function. Wrapper around function below.
-export const typedFnType = (instance, callback) => {
-  const [t, typesOfFns] = typedFnType2(callback);
-  const res = [
-    { i: instance, t },
-    ...typesOfFns,
-  ];
-  return res;
-};
 // Convenience function. Creates a function type, and also create Type-links for the function type (being typed by Function) and for all the nested function types. Saves a lot of code writing.
-export const typedFnType2 = callback => {
+export const typedFnType = (instance, callback, typeOfType = Type) => {
   const fnTs = [];
   const wrappedFnType = inType => outType => {
     const fnT = fnType(inType)(outType);
@@ -31,10 +22,15 @@ export const typedFnType2 = callback => {
     return fnT;
   };
   const t = callback(wrappedFnType); // force evaluation
-  return [
-    t,
-    fnTs.map(fnT => ({ i: fnT, t: Type })),
+  if (t.typeVars && typeOfType === Type) {
+    throw new Error("you probably meant to create a GenericType");
+  }
+  const res = [
+    { i: instance, t             },
+    { i: t       , t: typeOfType },
+    // ...fnTs.map(fnT => ({ i: fnT, t: Type })),
   ];
+  return res;
 };
 
 // Sum type
@@ -57,14 +53,20 @@ export const lsType = makeTypeConstructor(symbolList)(1);
 const symbolSet = Symbol('Set');
 export const setType = makeTypeConstructor(symbolSet)(1);
 
+
 // Pretty print type
 export function prettyT(type) {
   // console.log("pretty:", type);
+  if (typeof type === "symbol") {
+    return type.description;
+  }
   if (type.typeVars) {
     if (type.typeVars.size > 0) {
-      return `∀${[...type.typeVars].map(prettyT).join(", ")}: ${prettyT(type.type)}`;
+      return `∀(${[...type.typeVars].map(prettyT).join(", ")}): ${prettyT(type.type)}`;
+    }
+    else {
+      return prettyT(type.type);
     }
-    return prettyT(type.type);
   }
   if (type.symbol === symbolFunction) {
     return `${prettyT(type.params[0])} -> ${prettyT(type.params[1])}`;