GBNF

A library for parsing .gbnf grammar files in Javascript.

Install

npm install gbnf

Usage

Pass your grammar to GBNF:

import GBNF from 'gbnf';
const state = GBNF(`
root  ::= "yes" | "no"
`)

If the grammar is invalid, GBNF will throw.

GBNF returns a state representing the parsed state:

import GBNF from 'gbnf';
const state = GBNF(`
root  ::= "yes" | "no"
`)
for (const rule of state) {
  console.log(rule); 
  // { type: "CHAR", value: ["y".charCodeAt(0)]}
  // { type: "CHAR", value: ["n".charCodeAt(0)]}
}

state can be iterated over. (You can also call the iterator method directly with state.rules()). state cannot be indexed directly, but can easily be cast to an array with [...state] and indexed that way.

States are immutable. To parse a new token, call state.add():

import GBNF from 'gbnf';
let state = GBNF(`
root  ::= "I like green eggs and ham"
`)
console.log([...state]); // [{ type: "CHAR", value: ["I".charCodeAt(0)]}]
state = state.add("I li");
console.log([...state]); // [{ type: "CHAR", value: ["k".charCodeAt(0)]}]
state = state.add("ke gree");
console.log([...state]); // [{ type: "CHAR", value: ["n".charCodeAt(0)]}]

The possible rules returned include:

• CHAR - contains an array of either numbers representing code points to match, or an array of two numbers denoting a range within which a code point may appear.
• CHAR_EXCLUDED - contains an array of numbers representing code points not to match, or an array of two numbers denoting a range within which a code point may not appear.
• END - denotes a valid end of a string.