Parser Combinator Library

Bennu is a Javascript parser combinator library based on Parsec.

Parser combinators allow complex parsers to be created from a set of simple building blocks. Compared to other parsing techniques, combinatorial parsers can be written more quickly and integrate better with the host language.

// Very simple Brainfuck Bennuu parser in Khepri 
var op := oneOf '><+-.,';
var other := many <| noneOf "><+-.,[]"; // Brainfuck ignores any other characters 
var block := \body ->
    between(character '[', character ']',
var program := rec\self -> // allows referencing `program` in parse definition. 
        other,                   // consume non BF chars at start, 
        eager <| sepEndBy(other, // and between instructions and ending program 
                block self)));

Bennu provides many Parsec parser combinators. Bennu also provides functionality like memoization and running unmodified parser combinations incrementally..

  • parse-pn - Very simple polish notation calculator.
  • parse-ecma - Combinatory parsers for lexing and parsing ECMAScript 5.1
  • khepri - Khepri language lexers and parsers.
  • parse-re - ECMAScript regular expression grammar parser and engine using Bennu parser combinators.
  • parse-ecma-incremental - Demonstrates using unmodified parsers to incrementally lex ECMAScript.

Using Bennu

git clone bennu
cd bennu
git submodule update --init
$ npm install bennu


var parse = require('bennu').parse;
var text = require('bennu').text;

var aOrB = parse.either(
    text.character('b'));, 'b'); // 'b'

Include any AMD style module loader and load Bennu:

    paths: {
        'bennu': './dist',
        'nu-stream': './dependencies/nu/dist',
        'seshet': './dependencies/seshet/lib/seshet'
require(['bennu/parse'], function(parse) {

All files live in the top level 'parse' module.

Core functionality. Defines core parsers and data structures for creating and running parsers.

Parsers for working specifically with text.

Combinatory parsers for ordering parsers, like found in a language.

Running parsers incrementally.

Bennu parsers implement [Fantasy Land's][fs] monad, applicative, monoid and chain interfaces.

This can be used to directly . chain parsers instead of nested function calls:

var p = digit
     .chain(\x ->
        always(x + 5))
        always(x / 2));
run(p, '3'); // 4


Parse.js is written in Khepri. Khepri is an ECMAScript language focused on functional programming that compiles to Javascript. The dist directory contains the generated js library while the Khepri sources are in lib directory.