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* @author Juan Rodríguez Suárez <alu0101477596@ull.edu.es>
* @since 01/04/2024
* @module lexgen-code
* @file This module exports the functions buildLexer and nearleyLexer
* that allows to create lexical analyzers
*/
'use strict';
const hasNamedRegexp = /\(\?<[^<>()]+?>[^>]+\)/; // A regular expression with a named parenthesis
const isNamedRegexp = /^\(\?<[^<>()]+?>[^>]+\)$/; // A regular expression with a single named parenthesis
/**
* @description A helper function to check a regular expression has a
* named and only one named parenthesis and a body
* @param {RegExp} namedRegexp The regular expression
* @return {string | boolean} Whether the regular expression is named and has no named parenthesis inside
*/
const checkRegExpIsNamed = (namedRegexp) => {
if (hasNamedRegexp.test(namedRegexp.source)) {
if (isNamedRegexp.test(namedRegexp.source)) {
return true;
}
return 'A regular expression must have a single named parenthesis';
}
return 'A regular expression must be named';
};
/**
* Creates a lexical analyzer
* @param {array} regexps An array of regular expressions.
* Regexps must be named using a parenthesis. Example: `/(?<NAME>.)/`.
* The whole regexp must be inside the parenthesis.
* The names SPACE and ERROR are special:<br><br>
* 1. SPACE. If something matches a parenthesis named SPACE it will
* be ignored<br><br>
* 2. ERROR. It is a special value reserved for the implementation.
* When something doesn't match any of the provided regexps it will
* be returned as error. The error will span from the point where nothing
* matched to the next whitespace(\s)<br><br>
* **Note**: When two regexps can match the one that appears
* earlier will be chosen
* @throws {Error} Will throw if a regular expression isn't named
* or has more than one name
* @return {Object} The map of valid tokens and a lexical analyzer in form of a function
*/
const buildLexer = (regexps) => {
let validTokens = new Map();
regexps.push(/(?<ERROR>(.|\n)+)/);
regexps.forEach((regexp) => {
const NAME = checkRegExpIsNamed(regexp);
if (NAME === true) {
const tokenName = regexp.source.match(/\(\?<(.+?)>.+?\)/)[1];
validTokens.set(tokenName, regexp);
} else {
throw new Error(String(NAME));
}
});
const REGEXP = new RegExp(
regexps.map(r => r.source).join('|'), 'yu'
);
let lexer = (string, line = 1) => {
let match;
let tokens = [];
let actualColumn = -1;
while (match = REGEXP.exec(string)) {
let token = Array.from(validTokens.keys()).find(key => match.groups[key] !== undefined);
let newValue = match.groups[token];
if (newValue.includes('\n')) {
let lines = newValue.split('');
lines.forEach((char) => {
if (char === '\n') ++line;
});
if (token !== 'ERROR') actualColumn = match.index;
// Remove starting whitespaces which do not count for next line
for (let char of lines) {
if (char === '\n' || token === 'ERROR') {
break;
}
++actualColumn;
};
}
if (validTokens.get(token).skip) continue;
if (validTokens.get(token).value) {
newValue = validTokens.get(token).value(newValue);
}
tokens.push({ type: token, value: newValue, line: line, col: match.index - actualColumn, length: match[0].length });
}
return tokens;
};
return {validTokens, lexer};
};
const nearleyLexer = function(regexps, options) {
//debugger;
const {validTokens, lexer} = buildLexer(regexps);
validTokens.set("EOF");
return {
currentPos: 0,
buffer: '',
lexer: lexer,
validTokens: validTokens,
regexps: regexps,
/**
* Sets the internal buffer to data, and restores line/col/state info taken from save().
* Compatibility not tested
*/
reset: function(data, info) {
this.buffer = data || '';
this.currentPos = 0;
let line = info ? info.line : 1;
this.tokens = lexer(data, line);
let lastToken = {};
// Replicate the last token if it exists
Object.assign(lastToken, this.tokens[this.tokens.length-1]);
lastToken.type = "EOF"
lastToken.value = "EOF"
this.tokens.push(lastToken);
//console.log(this.tokens);
if (options && options.transform) {
if (typeof options.transform === 'function') {
debugger;
this.tokens = options.transform(this.tokens);
} else if (Array.isArray(options.transform)) {
options.transform.forEach(trans => this.tokens = trans(this.tokens))
}
}
return this;
},
/**
* Returns e.g. {type, value, line, col, …}. Only the value attribute is required.
*/
next: function() { // next(): Token | undefined;
if (this.currentPos < this.tokens.length)
return this.tokens[this.currentPos++];
return undefined;
},
has: function(tokenType) {
return validTokens.has(tokenType);
},
/**
* Returns an object describing the current line/col etc. This allows nearley.JS
* to preserve this information between feed() calls, and also to support Parser#rewind().
* The exact structure is lexer-specific; nearley doesn't care what's in it.
*/
save: function() {
return this.tokens[this.currentPos];
}, // line and col
/**
* Returns a string with an error message describing the line/col of the offending token.
* You might like to include a preview of the line in question.
*/
formatError: function(token) {
return `Error near "${token.value}" in line ${token.line}`;
} // string with error message
};
}
module.exports = { buildLexer, nearleyLexer };
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