74 lines
1.9 KiB
JavaScript
74 lines
1.9 KiB
JavaScript
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/**
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* A Pattern is a function that matches against a string starting at a given index.
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*
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* If it matches successfully, it returns some captured value, and the index following the match.
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*
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* @template T
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* @typedef {(source: string, index: number) => ([T, number] | null)} Peg.Pattern
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*/
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var Peg = {
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/**
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* Creates a pattern that wraps another pattern, transforming the returned value on a match
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* @template T, U
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* @param {Peg.Pattern<T>} pattern
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* @param {(value: T)=> U} map
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* @return {Peg.Pattern<U>}
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*/
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Map(pattern, map) {
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return function (source, index) {
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const match = pattern(source, index);
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return match ? [map(match[0]), match[1]] : null;
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};
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},
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/**
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* Creates a pattern matching a regex & returning any captures. The regex needs to be sticky (using the //y modifier)
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* @param {RegExp} regex
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* @return {Peg.Pattern<RegExpExecArray>}
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*/
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Regex(regex) {
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return function (source, index) {
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regex.lastIndex = index;
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const matches = regex.exec(source);
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return matches ? [matches, regex.lastIndex] : null;
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};
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},
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/**
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* @template T
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* @param {...Peg.Pattern<T>} patterns
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* @return {Peg.Pattern<T>}
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*/
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Choose(...patterns) {
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return function (source, index) {
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for (const pattern of patterns) {
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const match = pattern(source, index);
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if (match) {
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return match;
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}
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}
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return null;
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};
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},
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/**
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* @template {unknown[]} T
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* @param {{[K in keyof T]: Peg.Pattern<T[K]>}} patterns
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* @return {Peg.Pattern<T>}
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*/
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Sequence(...patterns) {
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return function (source, index) {
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const values = /** @type {T} */ (/** @type {unknown} */ ([]));
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for (const pattern of patterns) {
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const match = pattern(source, index);
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if (match == null) {
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return null;
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}
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values.push(match[0]);
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index = match[1];
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}
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return [values, index];
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};
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},
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};
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