chevrotain - Library

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chevrotain is an open source library created in 2015.

Source code:

git clone https://github.com/SAP/chevrotain

#372on PLDB

9Years Old

Parser Building Toolkit for JavaScript

chevrotain website
chevrotain is developed on GitHub and has 1,957 stars
chevrotain first developed in SAP

Example from the web:

"use strict"
/**
 * An Example of implementing a CSV Grammar with Chevrotain.
 *
 * Based on: https://github.com/antlr/grammars-v4/blob/master/csv/CSV.g4
 *
 * Note that this is a pure grammar without any actions (either embedded or via a CST Visitor).
 */
const { createToken, Lexer, Parser, EMPTY_ALT } = require("chevrotain")

// ----------------- lexer -----------------
const Text = createToken({ name: "Text", pattern: /[^,\n\r"]+/ })
const Comma = createToken({ name: "Comma", pattern: /,/ })
const NewLine = createToken({
    name: "NewLine",
    pattern: /\r?\n/
})
const String = createToken({ name: "String", pattern: /"(?:""|[^"])*"/ })

const allTokens = [Text, String, Comma, NewLine]
const CsvLexer = new Lexer(allTokens)

// Parser
class CsvParser extends Parser {
    constructor() {
        super(allTokens)

        // not mandatory, using $ (or any other sign) to reduce verbosity
        const $ = this

        $.RULE("csvFile", () => {
            $.SUBRULE($.hdr)
            $.AT_LEAST_ONE(() => {
                $.SUBRULE2($.row)
            })
        })

        $.RULE("hdr", () => {
            $.SUBRULE($.row)
        })

        $.RULE("row", () => {
            $.SUBRULE($.field)
            $.MANY(() => {
                $.CONSUME(Comma)
                $.SUBRULE2($.field)
            })
            $.CONSUME(NewLine)
        })

        $.RULE("field", () => {
            $.OR([
                { ALT: () => $.CONSUME(Text) },
                { ALT: () => $.CONSUME(String) },
                { ALT: EMPTY_ALT("empty field") }
            ])
        })

        // very important to call this after all the rules have been defined.
        // otherwise the parser may not work correctly as it will lack information
        // derived during the self analysis phase.
        this.performSelfAnalysis()
    }
}

// wrapping it all together
// reuse the same parser instance.
const parser = new CsvParser([])

module.exports = function(text) {
    // 1. Tokenize the input.
    const lexResult = CsvLexer.tokenize(text)

    // 2. Set the Parser's input
    parser.input = lexResult.tokens

    // 3. invoke the desired parser rule
    const cst = parser.csvFile()

    return {
        cst: cst,
        lexResult: lexResult,
        parseErrors: parser.errors
    }
}