prototype-3x5/peg.js

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2023-07-29 04:26:29 +00:00
/**
* A Pattern is a function that matches against a string starting at a given index.
*
* If it matches successfully, it returns some captured value, and the index following the match.
*
* @template T
* @typedef {(source: string, index: number) => ([T, number] | null)} Peg.Pattern
*/
var Peg = {
/**
* Creates a pattern that wraps another pattern, transforming the returned value on a match
* @template T, U
* @param {Peg.Pattern<T>} pattern
* @param {(value: T)=> U} map
* @return {Peg.Pattern<U>}
*/
Map(pattern, map) {
return function (source, index) {
const match = pattern(source, index);
return match ? [map(match[0]), match[1]] : null;
};
},
/**
* Creates a pattern matching a regex & returning any captures. The regex needs to be sticky (using the //y modifier)
* @param {RegExp} regex
* @return {Peg.Pattern<RegExpExecArray>}
*/
Regex(regex) {
return function (source, index) {
regex.lastIndex = index;
const matches = regex.exec(source);
return matches ? [matches, regex.lastIndex] : null;
};
},
/**
* @template T
* @param {...Peg.Pattern<T>} patterns
* @return {Peg.Pattern<T>}
*/
Choose(...patterns) {
return function (source, index) {
for (const pattern of patterns) {
const match = pattern(source, index);
if (match) {
return match;
}
}
return null;
};
},
/**
* @template {unknown[]} T
* @param {{[K in keyof T]: Peg.Pattern<T[K]>}} patterns
* @return {Peg.Pattern<T>}
*/
Sequence(...patterns) {
return function (source, index) {
const values = /** @type {T} */ (/** @type {unknown} */ ([]));
for (const pattern of patterns) {
const match = pattern(source, index);
if (match == null) {
return null;
}
values.push(match[0]);
index = match[1];
}
return [values, index];
};
},
};