Pegjs-import NPM

pegjs-import

Import other PEG files into a PEG.js grammar.

Installation

npm install --save pegjs pegjs-import

Usage

pegjs-import provides a single function that replaces peg.buildParser:

  var pegimport = require('pegjs-import');

  var parser = pegimport.buildParser('path/to/grammar.peg', options);
  parser.parse('foo');

Instead of taking a string, it takes a filename.

Inside a PEG.js grammar, you can now make use of the @import directive, like so:

/* NOTE: this grammar won't work in stock PEG.js anymore! */

{
  this.notes = "Initializers work as you expect them to and are imported.";
}

@import "path/to/grammar"

start
  = grammar

When you @import another grammar, that grammar's topmost rule becomes accessible in the context of the current grammar under one of two possible rule names:

A name you provide explicitly through the use of the optional "as" parameter
The basename of the file, corrected to be a valid Javascript identifier (so if the file were called /foo/bar/my-grammar.peg, the rule name would be my_grammar).

Changes from stock PEG.js behavior

You cannot supply options.allowedStartRules anymore. The only allowed start rule is always the first rule in the grammar.
You cannot supply a grammar as a string, you must give a filename. There are libraries that provide virtual and in-memory filesystems if you want to work on grammars as strings.

Limitations

pegjs-import is only tested on NodeJS, though the parsers work everywhere they usually do.
Circular dependencies explicitly throw an exception. Don't use them.
Please don't do funny things with rule names, pegjs-import will probably explode. I will not be held responsible for exploding grammars.