71 lines
7.3 KiB
JavaScript
71 lines
7.3 KiB
JavaScript
"use strict";
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Object.defineProperty(exports, "__esModule", { value: true });
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exports.match = exports.when = exports.CaseSwitch = void 0;
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class Case {
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constructor(type, fn) {
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this.type = type;
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this.fn = fn;
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}
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}
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class CaseSwitch {
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constructor(cases) {
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if (cases.length === 0) {
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throw new Error("must have at least one case");
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}
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this.cases = cases;
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}
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// implemented lazily because not every CaseSwitch will be used
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get accept() {
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if (this.memoAccept) {
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return this.memoAccept;
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}
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const cases = this.cases;
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let type = cases[0].type;
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for (let i = 1; i < cases.length; i++) {
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type = type.or(cases[i].type);
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}
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this.memoAccept = type;
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return this.memoAccept;
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}
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run(val) {
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for (let c of this.cases) {
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if (c.type.guard(val)) {
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return c.fn(val);
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}
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}
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// raise a type error if none of the cases match the value.
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this.accept.assert(val);
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/* istanbul ignore next */ throw "unreachable";
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}
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/**
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* Create a new CaseSwitch that also handles the specified case.
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*/
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when(type, fn) {
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const c = new Case(type, fn);
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return new CaseSwitch([...this.cases, c]);
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}
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}
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exports.CaseSwitch = CaseSwitch;
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/**
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* Create a type switch that can be used with `match()`.
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*/
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function when(type, fn) {
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const c = new Case(type, fn);
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return new CaseSwitch([c]);
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}
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exports.when = when;
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/**
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* Match a value against a type switch created with `when()`.
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*
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* @example
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* const asString = t.match(foo,
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* t.when(t.array(t.str), xs => xs.join(' and '))
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* .when(t.str, s => s)
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* .when(t.any, x => '' + x))
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*/
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// export function match<I, O, Cases extends Case<I, O>>(val: I, cases: CaseSwitch<Cases>): O {
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function match(val, sw) {
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return sw.run(val);
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}
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exports.match = match;
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