add nominal types for 2D points

type_registry.js

@@ -2,6 +2,7 @@
 // Maybe we shouldn't use Symbols for types, but we also cannot use primitive values for types because they may accidentally overlap with 'real' values (that are not types)
 // We also cannot use objects for types because similar to Symbols, objects are only equal to themselves if we use them as Map keys.
 
+import { Function } from "./metacircular.js";
 import { DefaultMap } from "./util.js";
 
 // Global store of function types:
@@ -18,6 +19,19 @@ export const fnType = ({in: inType, out: outType}) => {
   }
 };
 
+export const typedFnType = (instance, callback) => {
+  const fnTs = [];
+  const wrappedFnType = ({in: inType, out: outType}) => {
+    const fnT = fnType({in: inType, out: outType});
+    fnTs.push(fnT);
+    return fnT;
+  }
+  return [
+    {i: instance, t: callback(wrappedFnType)},
+    ...fnTs.map(fnT => ({i: fnT, t: Function})),
+  ];
+}
+
 // Global store of list types:
 const listTypes = new Map();
 export const lsType = (elementType) => {