add type comparison function

compare/primitives.js

@@ -1,5 +1,7 @@
 // Total ordering of primitive types
 
+import { getSymbol } from "../type_constructor.js";
+
 export const compareNumbers = x => y => {
   if (typeof(x) !== 'number' || typeof(y) !== 'number') {
     throw new Error(`was only meant to compare numbers! got ${x} and ${y}`);
@@ -23,3 +25,13 @@ export const compareBools = x => y => {
 
 // The Unit-type has only one instance, which is equal to itself:
 export const compareUnits = x => y => 0;
+
+export const compareTypes = x => y => {
+  return compareSymbols(getSymbol(x))(getSymbol(y))
+    || compareNumbers(x.params.length)(y.params.length)
+    || x.params.reduce((acc, _, i) => acc || compareTypes(x.params[i])(y.params[i]), 0)
+}
+
+// Note: dirty assumption that every symbol has unique description.
+// This will be fixed once we move from symbols to real UUIDs.
+export const compareSymbols = a => b => (a !== b) && compareStrings(a.description)(b.description);