can auto-generate comparison functions for composed types

compare/primitives.js

@@ -1,4 +1,4 @@
-import { Char, Double, Int } from "../primitives/types.js";
+import { Char, Double, Int, Unit } from "../primitives/types.js";
 
 export const compareNumbers = x => y => {
   if (typeof(x) !== 'number' || typeof(y) !== 'number') {
@@ -21,9 +21,5 @@ export const compareBools = x => y => {
   return x - y;
 };
 
-export const typeToCmp = new Map([
-  [Int, compareNumbers],
-  [Char, compareStrings],
-  [Double, compareNumbers],
-  [Boolean, compareBools],
-]);
+// The Unit-type has only one instance, which is equal to itself:
+export const compareUnits = x => y => 0;

compare/registry.js

@@ -0,0 +1,25 @@
+import { SymbolBool, SymbolChar, SymbolDouble, SymbolInt, SymbolUnit } from "../primitives/types.js";
+import { symbolList, symbolProduct, symbolSet, symbolSum } from "../structures/types.js";
+import { compareBools, compareNumbers, compareStrings, compareUnits } from "./primitives.js";
+import { compareLists, compareProducts, compareSets, compareSums } from "./structures.js";
+
+const typeSymbolToCmp = new Map([
+  [SymbolInt   , compareNumbers],
+  [SymbolChar  , compareStrings],
+  [SymbolDouble, compareNumbers],
+  [SymbolBool  , compareBools],
+  [SymbolUnit  , compareUnits],
+
+  // these functions take extra comparison callbacks:
+  [symbolList   , compareLists],
+  [symbolProduct, compareProducts],
+  [symbolSum    , compareSums],
+  [symbolSet    , compareSets],
+])
+
+export const makeCompareFn = type => {
+  return type.params.reduce(
+    (acc, cur) => acc(makeCompareFn(cur)),
+    typeSymbolToCmp.get(type.symbol)
+  );
+}

compare/structures.js

@@ -1,8 +1,10 @@
 import { compareNumbers } from "./primitives.js"
-import { length as lengthLs } from "../structures/list.js";
+import { get, length as lengthLs } from "../structures/list.js";
 import { read, length as lengthSet } from "../structures/set.js";
 import { constructorProduct, getLeft, getRight } from "../structures/product.js";
 import { match } from "../structures/sum.js";
+import { makeGeneric } from "../generics/generics.js";
+import { lsType } from "../structures/types.js";
 
 // (a -> a -> Int) -> [a] -> [a] -> Int
 export const compareLists = compareElems => x => y => {