msluther/pegjs-otf

On-The-Fly Compilation for PEG.js

pegjs-otf

This is a small wrapper class around the PEG.js API and a companion Browserify transform for on-the-fly (OTF) compiling PEG.js grammars into parser code under a syntactically identical usage for both Node/NPM and Browser/Browserify environments.

Installation

$ npm install pegjs-otf
$ npm install browserify

Usage

With a sample grammar sample.pegjs like this...

sample
    = _ "hello" _ who:[A-Za-z]+ _ { return who.join(""); }

_ "blank"
    = (co / ws)*

co "comment"
    = "//" (![\r\n] .)*
    / "/*" (!"*/" .)* "*/"

ws "whitespaces"
    = [ \t\r\n]+

...instead of using a sample.js driver...

var PEG = require("pegjs-otf");
var fs = require("fs");
var parser = PEG.generate(
    fs.readFileSync(__dirname + "/sample.pegjs", "utf8"),
    { optimize: "size" }
);
console.log(parser.parse("hello world") === "world" ? "OK" : "FAIL");

...now use a sample.js driver like this:

var PEG = require("pegjs-otf");
var parser = PEG.generateFromFile(
    __dirname + "/sample.pegjs",
    { optimize: "size" }
);
console.log(parser.parse("hello world") === "world" ? "OK" : "FAIL");

Then it will work in both Node (through on-the-fly run-time compilation)...

$ node sample.js
OK

...and the Browser (with the help of Browserify through on-the-fly compile-time compilation):

$ browserify -t pegjs-otf/transform -o sample.browser.js sample.js
$ node sample.browser.js
OK

Intention & How It Works

The API returned by require("pegjs-otf") is really just the PEG.js API with an additional injected method generateFromFile(filename, options). And this generateFromFile(filename, options) is actually not really some sort of an important convenience function, because it technically is just require("pegjs").generate(require("fs").readFileSync(filename), options) and this would not warrant an extra wrapper API, of course. Instead the pegjs-otf module and its distinct generateFromFile method is actually a marker.

In a regular Node environment it really just performs its simple require("pegjs").generate(require("fs").readFileSync(filename), options) operation. But when the application code is transpiled for a Browser environment with the help of the excellent Browserify, then the pegjs-otf/transform transform can kick in and replaces the var xx = require("pegjs-otf") call with nothing and the xx.generateFromFile(filename, options) call with the corresponding on-the-fly compiled parser code.

This way you need no extra build-time step for neither Node nor Browser environments just because of PEG.js usage. And both Node and Browser environments behave identically without having to alter the source.

Rationale

There is another Browserify transform named browserify-pegjs which transpiles require("sample.pegjs") calls into the actual on-the-fly compiled parser code. It has two drawbacks compared to pegjs-otf: this is fine for Browser environments, but it fails in regular Node environments and the only way to pass options to PEG.js' generate is via external Browserify options.

The second of the two above drawbacks cannot be resolved. The first of the two above drawbacks can be circumvented with another module named pegjs-require. Unfortunately, this has the same drawback as browserify-pegjs: it also does not allow the passing of options to the underlying generate method.

For those reasons I've written pegjs-otf, as it supports both Node and Browserify environments and allows the passing of options to generate.

License

Copyright (c) 2014-2019 Dr. Ralf S. Engelschall (http://engelschall.com/)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.