type inferencing "unifying" operation is now bi-directional + begin writing generic version of "unifying" operation (that should work on all types)

typeclasses/eq.js

@@ -0,0 +1,38 @@
+import { makeGeneric } from "../generics/generics";
+import { Type, typedFnType } from "../metacircular";
+import { Bool, Byte, Char, Double, Int } from "../primitives/symbols";
+import { deepEqual } from "../util";
+import { eqDictType } from "./eq_type";
+
+export const getEq = numDict => numDict.eq;
+
+export const ModuleEq = {l:[
+  ...typedFnType(eqDictType, fnType => fnType({in: Type, out: Type})),
+
+  ...typedFnType(getEq, fnType => makeGeneric(a =>
+    fnType({
+      in: eqDictType(a),
+      out: fnType({
+        in: a,
+        out: fnType({
+          in: a,
+          out: Bool,
+        }),
+      }),
+    }))),
+]};
+
+// all our data (and types) are encoded such that we can test equality the same way:
+
+const eq = x => y => deepEqual(x,y);
+
+const EqDict = {eq};
+
+export const EqInstances = new Map([
+  [Int, EqDict],
+  [Bool, EqDict],
+  [Double, EqDict],
+  [Byte, EqDict],
+  [Char, EqDict],
+  [Type, EqDict],
+]);

typeclasses/eq_type.js

@@ -0,0 +1,4 @@
+import { DefaultMap } from "../util.js";
+
+const eqDictTypeRegistry = new DefaultMap(a => ({ eqDict: a }));
+export const eqDictType = a => eqDictTypeRegistry.getdefault(a, true);

typeclasses/num.test.js

@@ -2,6 +2,7 @@ import { assign } from "../generics/generics.js";
 import { makeGeneric } from "../generics/generics.js";
 import { fnType } from "../metacircular.js";
 import { Double, Int } from "../primitives/symbols.js";
+import { getMul, NumInstances } from "./num.js";
 import { numDictType } from "./num_type.js";
 
 const square = numDict => x => getMul(numDict)(x)(x);
@@ -21,3 +22,7 @@ console.log(assign(squareFnType, makeGeneric(() => numDictType(Int))));
 // should be: Double -> Double
 console.log(assign(squareFnType, makeGeneric(() => numDictType(Double))));
 
+// to call 'square' we need:
+//   - access to a mapping from types to their typeclass instantiation
+//   - to know that our argument is 'Int'
+console.log(square(NumInstances.get(Int))(42n)); // 1764n