75 lines
2.3 KiB
JavaScript
75 lines
2.3 KiB
JavaScript
import { compareStrings } from "../compare/primitives.js";
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import { unit } from "../primitives/unit.js";
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import { capitalizeFirstLetter } from "../util/util.js";
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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 = variantNames => {
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if (variantNames.length === 0) {
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return _ => {
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throw new Error("Bottom!");
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};
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}
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return enumm => {
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return matchFn(enumm, variantNames);
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}
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};
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const matchFn = (enumm, variantNames) => {
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const [variantName, ...remaining] = variantNames;
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return handler => {
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if (enumm.variant === variantName) {
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return eatParameters(
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remaining.length,
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handler(enumm.value));
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}
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else {
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return matchFn(enumm, remaining);
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}
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};
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};
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export const symbolElse = Symbol('else');
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export const makeNiceMatchFn = (variantNames) => handlers => enumm => {
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const incomplete = variantNames.filter(({l: variant}) => !handlers.hasOwnProperty(variant)).length > 0;
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if (incomplete && !handlers.hasOwnProperty(symbolElse)) {
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throw new Error("if not every variant is handled, must have 'else' handler");
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}
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if (!incomplete && handlers.hasOwnProperty(symbolElse)) {
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console.warn("'else' handler will never be invoked because every variant is already handled");
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}
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for (const [variant, handler] of Object.entries(handlers)) {
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if (enumm.variant === variant) {
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return handler(enumm.value);
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}
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}
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return handlers[symbolElse](unit);
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}
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export const makeConstructors = variantNames => {
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if (new Set(variantNames).size !== variantNames.length) {
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throw new Error("precondition failed: non-unique variant names");
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}
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return variantNames.map(variantName => {
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const ctorName = `new${capitalizeFirstLetter(variantName)}`;
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const ctor = { [ctorName]: value => ({variant: variantName, value}) }[ctorName];
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return ctor;
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})
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};
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export const makeEnumCompareFn = variantCompares => {
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return enumA => enumB => {
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const cmp = compareStrings(enumA.variant)(enumB.variant);
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if (cmp !== 0) {
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return cmp;
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}
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const getCompareFn = variantCompares.find(({l: variantName}) => variantName === enumA.variant).r;
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return getCompareFn()(enumA.value)(enumB.value);
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}
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};
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