simplify 'enum'

README.txt

@@ -0,0 +1,3 @@
+Browser and NodeJS compatible library.
+
+Tests require NodeJS.

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;
+  })
 };

lib/structures/enum.types.js

@@ -1,10 +1,9 @@
-import { makeCompareFn } from "../compare/dynamic.js";
 import { makeGeneric } from "../generics/generics.js";
 import { newDynamic } from "../primitives/dynamic.js";
-import { Bottom } from "../primitives/primitive_types.js";
+import { zip } from "../util/util.js";
 import { makeConstructors, makeMatchFn } from "./enum.js";
-import { getRight } from "./product.js";
-import { fnType, sumType } from "./type_constructors.types.js";
+import { getLeft, getRight } from "./product.js";
+import { fnType } from "./type_constructors.types.js";
 
 // 'variants' is an array of (name: string, type: Type) pairs.
 // e.g., the list of variants:
@@ -14,39 +13,39 @@ import { fnType, sumType } from "./type_constructors.types.js";
 // results in the type:
 //   (Int | ([Int] | (Unit | ⊥)))
 
-const _enumType = rootSelf => variants => {
-  // console.log("enumType..", variants);
-  if (variants.length === 0) {
-    return Bottom; // empty enum is equal to Bottom-type (cannot be instantiated)
-  }
-  const [variant, ...rest] = variants;
-  const variantType = getRight(variant);
-  return sumType
-    (self => {
-      // console.log("requested left type (of enumType)")
-      return variantType(rootSelf || self);
-    })
-    (self => {
-      // console.log("requested right type (of enumType)")
-      return _enumType(self)(rest)
-    });
-};
+// const _enumType = rootSelf => variants => {
+//   // console.log("enumType..", variants);
+//   if (variants.length === 0) {
+//     return Bottom; // empty enum is equal to Bottom-type (cannot be instantiated)
+//   }
+//   const [variant, ...rest] = variants;
+//   const variantType = getRight(variant);
+//   return sumType
+//     (self => {
+//       // console.log("requested left type (of enumType)")
+//       return variantType(rootSelf || self);
+//     })
+//     (self => {
+//       // console.log("requested right type (of enumType)")
+//       return _enumType(self)(rest)
+//     });
+// };
 
-export const enumType = _enumType(null);
+// export const enumType = _enumType(null);
 
 export const makeConstructorTypes = type => variants => {
   return variants.map(variant => {
     const variantType = getRight(variant);
     return fnType(_ => variantType)(_ => type);
   });
-}
+};
 
 export const makeMatchFnType = type => variants => {
-  return makeGeneric(resultType =>
+  return makeGeneric(a =>
     fnType
       (_ => type)
-      (_ => handlerType(resultType)(type)(variants)));
-}
+      (_ => handlerType(a)(type)(variants)));
+};
 
 const handlerType = resultType => type => variants => {
   if (variants.length === 0) {
@@ -57,25 +56,24 @@ const handlerType = resultType => type => variants => {
   return fnType
       (_ => fnType(_ => variantType)(_ => resultType)), // handler
       (_ => handlerType(resultType)(type)(rest));  // rest
-}
+};
 
 export const makeModuleEnum = type => variants => {
-  const ctors = makeConstructors(variants);
+  const variantNames = variants.map(getLeft);
+  const ctors = makeConstructors(variantNames);
   const ctorTypes = makeConstructorTypes(type)(variants);
-  const matchFn = makeMatchFn(variants);
+  const matchFn = makeMatchFn(variantNames);
   const matchFnType = makeMatchFnType(type)(variants);
   const module = [
-    // ["type", newDynamic(type)(Type)],
-
     // constructors:
     ...zip(ctors, ctorTypes)
       .map(([ctor, ctorType]) => ["ctor", newDynamic(ctor)(ctorType)]),
 
     // match-function:
-    newDynamic(matchFn, matchFnType),
+    ["match", newDynamic(matchFn)(matchFnType)],
 
-    // compare-function:
-    newDynamic(makeCompareFn(enumType(variants)))
+    // // compare-function:
+    // newDynamic(makeCompareFn(enumType(variants)))
   ];
   return module;
-}
+};

lib/structures/product.js

@@ -4,6 +4,6 @@
 // Product-types of more fields (called Structs) can be constructed by nesting Product-types.
 
 // In JS, all products are encoded in the same way:
-export const newProduct = l => r => ({l, r});
+export const newProduct = l => r => ({l, r}); // <-- apparently, this object-based encoding is faster than array-based, in both FF and Chrome.
 export const getLeft     = product => product.l;
 export const getRight    = product => product.r;

tests/enum.js

@@ -0,0 +1,46 @@
+import { makeTypeConstructor } from "../lib/meta/type_constructor.js";
+import { Char, Double, Unit } from "../lib/primitives/primitive_types.js";
+import { unit } from "../lib/primitives/unit.js";
+import { makeModuleEnum } from "../lib/structures/enum.types.js";
+import { newProduct } from "../lib/structures/product.js";
+import { lsType } from "../lib/structures/type_constructors.types.js";
+
+import assert from "node:assert";
+
+const variants = [
+  newProduct("fever")(_ => Double),
+  newProduct("confused")(_ => Unit),
+  newProduct("other")(_ => lsType(_ => Char)),
+];
+
+const symbolSymptom = "Symptom__c0442736bb6f11ae99a51b14e4db44b4";
+
+const Symptom = makeTypeConstructor(symbolSymptom)(0);
+
+const [
+  // constructors
+  [, {i: newFever}],
+  [, {i: newConfused}],
+  [, {i: newOther}],
+
+  // match function
+  [, {i: matchSymptom}],
+] = makeModuleEnum(Symptom)(variants);
+
+const fever = newFever(38.5);
+const confused = newConfused(unit);
+const other = newOther("sweating");
+
+console.log("observe the encoding of different variant instances:");
+console.log(" ", fever);
+console.log(" ", confused);
+console.log(" ", other);
+
+const description = symptom => matchSymptom(symptom)
+  (fever => `Fever (${fever} degrees)`)
+  (_confused => `Confused`)
+  (other => `Other: ${other}`);
+
+assert.strictEqual("Fever (38.5 degrees)", description(fever));
+assert.strictEqual("Confused"            , description(confused));
+assert.strictEqual("Other: sweating"     , description(other));

tests/struct.js

@@ -5,7 +5,7 @@ import { Bool, Char, Int } from "../lib/primitives/primitive_types.js";
 import { makeModuleStruct } from "../lib/structures/struct.types.js";
 import { lsType } from "../lib/structures/type_constructors.types.js";
 
-
+// Nominal type
 const symbolPerson = "Person__22a59ca589b4a7efdbe20b52f380e50f";
 
 const Person = makeTypeConstructor(symbolPerson)(0);