basic functionality, no generics

function_registry.js

@@ -0,0 +1,15 @@
+import { DefaultMap } from "./util.js";
+
+const mapping = new DefaultMap(() => new Map());
+
+export const getFnType = (inType, outType) => {
+  const m2 = mapping.getdefault(inType);
+  if (m2.has(outType)) {
+    return m2.get(outType);
+  }
+  else {
+    const fnType = {in: inType, out: outType};
+    m2.set(outType, fnType);
+    return fnType;
+  }
+}