57 lines
1.8 KiB
JavaScript
57 lines
1.8 KiB
JavaScript
import { Bottom } from "../primitives/types.js";
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import { capitalizeFirstLetter } from "../util/util.js";
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import { constructorProduct, getLeft, getRight } from "./product.js";
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import { constructorLeft, constructorRight, match } from "./sum.js";
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import { sumType } from "./types.js";
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// 'variants' is an array of (name: string, type: Type) pairs.
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// e.g., the list of variants:
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// [ { l: "price" , r: Int },
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// { l: "prices" , r: [Int] },
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// { l: "not_found", r: Unit } ]
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// results in the type:
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// (Int | ([Int] | (Unit | ⊥)))
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export const enumType = variants => {
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if (variants.length === 0) {
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return Bottom; // empty enum is equal to Bottom-type (cannot be instantiated)
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}
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const [variant, ...rest] = variants;
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const variantType = getRight(variant);
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return sumType(variantType)(enumType(rest));
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};
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const eatParameters = (numParams, result) => {
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if (numParams === 0) {
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return result;
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}
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else return () => eatParameters(numParams-1, result);
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}
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export const makeMatchFn = variants => {
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if (variants.length === 0) {
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return undefined;
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}
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const [_, ...remainingVariants] = variants;
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return sum => handler => {
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return (
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match(sum)(constructorProduct
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(leftValue => eatParameters(remainingVariants.length, handler(leftValue)))
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(rightValue => makeMatchFn(remainingVariants)(rightValue))
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));
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};
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};
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export const makeConstructors = variants => {
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if (variants.length === 0) {
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return [];
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}
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const [variant, ...remainingVariants] = variants;
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const name = getLeft(variant);
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const ctorName = `new${capitalizeFirstLetter(name)}`;
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const constructor = { [ctorName]: val => constructorLeft(val) }[ctorName];
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return [
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constructor,
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...makeConstructors(remainingVariants).map(ctor =>
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({[ctor.name]: val => constructorRight(ctor(val))}[ctor.name])),
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];
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}
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