TS PEG.js

TS PEG.js is a TS code generation plugin for peggy.

Requirements

• peggy (previous versions use: pegjs)

Installation

Node.js

Installs ts-pegjs + peggy

$ npm install ts-pegjs

Usage

Generating a Parser from JS code

In Node.js, require both the peggy parser generator and the ts-pegjs plugin:

var peggy = require('peggy');
var tspegjs = require('ts-pegjs');

To generate a TS parser, pass to pegjs.generate ts-pegjs plugin and your grammar:

var parser = pegjs.generate("start = ('a' / 'b')+", {
    output: 'source',
    format: 'commonjs',
    plugins: [tspegjs],
    tspegjs: {
        customHeader: "// import lib\nimport { Lib } from 'mylib';"
    }
});

The method will return source code of generated parser as a string.

Supported options of pegjs.generate:

• cache — if true, makes the parser cache results, avoiding exponential parsing time in pathological cases but making the parser slower (default: false). This is strongly recommended for big grammars (like javascript.pegjs or css.pegjs in example folder)
• allowedStartRules — rules the parser will be allowed to start parsing from (default: the first rule in the grammar)

Plugin options

Note: Options in CLI mode are written in POSIX (long names as kebab-case) convention e.g. --custom-header but with camelcase on JavaScript e.g. customHeader.

• customHeader — A string or an array of strings which are a valid TS code to be injected on the header of the output file. E.g. provides a convenient place for adding library imports.
• customHeaderFile — A header file to include.
• errorName — The name of the exported internal error class to override. The default value from version 3.0.0 is PeggySyntaxError. Previous one was SyntaxError.
• returnTypes — An object containing rule names as keys and a valid TS return type as string.
• skipTypeComputation — Boolean. If true, ts-pegjs will not try to use TS to infer types based on your grammar rules.
• onlyGenerateGrammarTypes — Boolean. If true, only types for your grammar rules (and no parser) will be generated. Cannot be used with skipTypeComputation.
• doNotCamelCaseTypes — Boolean. By default type names for grammar rules are converted to CamelCase. If true, this conversion is not done and type names will match the casing of your grammar rules.

Generating a Parser from CLI

Sample usage:

peggy --plugin ./src/tspegjs -o examples/arithmetics.ts --cache examples/arithmetics.pegjs

(Note ./src/tspegjs is the path to tspegjs.ts in the project. If you installed ts-pegjs using npm, it should probably be ./node_modules/ts-pegjs/src/tspegjs.)

It will generarate the parser in the TS flavour.

If you need to pass specific plugin options you can use the option --extra-options-file provided by pegjs and pass it a filename (e.g. pegconfig.json) containing specific options like the following JSON sample:

peggy --plugin ./src/tspegjs --extra-options-file pegconfig.json -o examples/arithmetics.ts --cache examples/arithmetics.pegjs

{
    "tspegjs": {
        "customHeader": "// import lib\nimport { Lib } from 'mylib';"
    },
    "returnTypes": {
        "Integer": "number",
        "Expression": "number",
    }
}

For rules not listed in returnTypes object any type is declared by default.

Make sure to pass any additional CLI options, like --extra-options-file before the parameter -o as these will otherwise be treated as arguments to that one.

Using the Parser

1. Save parser generated by pegjs.generate to a file or use the one generated from the CLI tool.

2. In client TS code:

import { PeggySyntaxError, parse } from './arithmetics';

try {
    const sampleOutput = parse('my sample...');
} catch (ex: PeggySyntaxError) {
    // Handle parsing error
    // [...]
}

Changelog

Changelog.

Acknowledgments

Thanks to:

• David Majda for creating pegjs
• Elantcev Mikhail for providing the pegjs PHP plugin, inspiration on this one.

License

The MIT License (MIT)

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(c) 2017-2023, Pedro J. Molina at metadev.pro