chevrotain - Library

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chevrotain is an open source library created in 2015.

#609on PLDB

9Years Old

Download source code:

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

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Parser Building Toolkit for JavaScript

Tags: library
chevrotain is developed on GitHub and has 2,450 stars
Early development of chevrotain happened in SAP
chevrotain is written in TypeScript, JavaScript, Markdown, JSON, HTML, YAML, Bourne shell, CSS, JSON5, CSV

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
    }
}