simplify 'enum'

lib/structures/enum.js

@@ -1,6 +1,4 @@
 import { capitalizeFirstLetter } from "../util/util.js";
-import { newProduct as newProduct, getLeft } from "./product.js";
-import { newLeft, newRight, match } from "./sum.js";
 
 const eatParameters = (numParams, result) => {
   if (numParams === 0) {
@@ -9,29 +7,38 @@ const eatParameters = (numParams, result) => {
   else return () => eatParameters(numParams-1, result);
 }
 
-export const makeMatchFn = variants => {
-  if (variants.length === 0) {
-    throw new Error("Bottom!");
+export const makeMatchFn = variantNames => {
+  if (variantNames.length === 0) {
+    return _ => {
+      throw new Error("Bottom!");
+    };
   }
-  const [_, ...remainingVariants] = variants;
-  return sum => handler => {
-    return match(sum)
-        (leftValue => eatParameters(remainingVariants.length, handler(leftValue)))
-        (rightValue => makeMatchFn(remainingVariants)(rightValue));
+  return enumm => {
+    return matchFn(enumm, variantNames);
+  }
+};
+
+const matchFn = (enumm, variantNames) => {
+  const [variantName, ...remaining] = variantNames;
+  return handler => {
+    if (enumm.variant === variantName) {
+      return eatParameters(
+        remaining.length,
+        handler(enumm.value));
+    }
+    else {
+      return matchFn(enumm, remaining);
+    }
   };
 };
 
-export const makeConstructors = variants => {
-  if (variants.length === 0) {
-    return [];
+export const makeConstructors = variantNames => {
+  if (new Set(variantNames).size !== variantNames.length) {
+    throw new Error("precondition failed: non-unique variant names");
   }
-  const [variant, ...remainingVariants] = variants;
-  const name = getLeft(variant);
-  const ctorName = `new${capitalizeFirstLetter(name)}`;
-  const constructor = { [ctorName]: val => newLeft(val) }[ctorName];
-  return [
-    constructor,
-    ...makeConstructors(remainingVariants).map(ctor =>
-      ({[ctor.name]: val => newRight(ctor(val))}[ctor.name])),
-  ];
+  return variantNames.map(variantName => {
+    const ctorName = `new${capitalizeFirstLetter(variantName)}`;
+    const ctor = { [ctorName]: value => ({variant: variantName, value}) }[ctorName];
+    return ctor;
+  })
 };