ReParse

ReParse is a parser combinator library for Javascript like Haskell's Parsec.

Installation

Download lib/reparse.js and add it to your project or use npm install reparse.

API

To use ReParse, construct a new ReParse(input) object, then call the .start() method, passing it the top-level production of your grammar. Each production may be a RegExp or a function.

A RegExp will produce the first captured group or the entire value it matched if there are no groups. Functions are called with this bound to the parser. They take no arguments. A function should invoke one or more parser methods, optionally transforming the results into an appropriate return value.

Here is a grammar for a subset of JSON that supports arrays and positive integers. See examples/json.js for a more complete example:

// e.g: parse("[1, [2]]")
var ReParse = require('reparse');

function parse(data) {
  return (new ReParse(data, true)).start(value);
}

function value() {
  return this.choice(number, array);
}

function array() {
  return this.between(/^\[/, /^\]/, elements);
}

function elements() {
  return this.sepBy(value, /^,/);
}

function number() {
  return parseInt(this.match(/^\d+/));
}

ReParse indicates failure internally using exceptions, so it's safe to use the result of any production immediately without checking for an error state.

ReParse(input, [ignorews])

Create a new parser for an input string. If ignorews is true, skip whitespace before and after each production.

.start(method)

Return the value produced by method. All input must be consumed.

.eof()

Return true if the input is exhausted.

.fail()

Calling this method indicates that a production has failed; an exception will be raised and caught by the previous production.

.produce(method)

Apply the production method to the input and return the result.

.maybe(method)

Apply the production method to the input and return the result. If method fails, restoring the input to its previous state.

.option(method, otherwise)

Try to produce method. If it fails, restore the input and return otherwise.

.match(regexp)

Match a regular expression against the input, returning the first captured group. If no group is captured, return the matched string.

.choice(alt1, alt2, ...)

Try alternatives from left to right, returning the value of the first one that's successful.

.seq(p1, p2, ...)

Apply a sequence of productions from left to right. They must all succeed. Return an array of capture groups (like a regular expression match would). Index 0 is the entire matched string, index 1 corresponds to p1, etc.

.many(method)

Return an array of zero or more values produced by method.

.many1(method)

Return an array of one or more values produced by method.

.between(left, right, body)

This is equivalent to .seq(left, body, right)[2].

.skip(method)

Ignore zero or more instances of method. Return the parser object.

.skip1(method)

Ignore one or more instances of method. Return the parser object.

.skipWS()

Ignore whitespace. Return the parser object.

.sepBy(method, sep)

Return an array of zero or more values produced by method. Each value is separated by sep.

.sepBy1(method, sep)

Return an array of one or more values produced by method. Each value is separated by sep.

.endBy(method, end)

This is equivalent to .many(method) followed by .option(end).

.endBy1(method, end)

This is equivalent to .many1(method) followed by .option(end).

.sepEndBy(method, sep)

Return an array of zero or more values produced by method. Each value is separated by sep and the entire sequence is optionally terminated by sep.

.sepEndBy1(method, sep)

Return an array of one or more values produced by method. Each value is separated by sep and the entire sequence is optionally terminated by sep.

.chainl(method, op, [otherwise])

This can be used to eliminate direct left-recursion. Parse zero or more values produced by method and separated by op. Returns a value obtained by left associative application of functions returned by op. If zero values are produced, return otherwise.

.chainl1(method, op)

Like .chainl, but at least one value must be produced by method. For example, this grammar:

expr   ::= expr '+' term | term
term   ::= term '*' factor | factor

Might be implemented like this (see examples/calc.js):

function expr() {
  return this.chainl1(term, addop);
}

function term() {
  return this.chainl1(factor, mulop);
}

function factor() {
  ...
}

Compatibility

ReParse has been tested with Node.JS version v0.1.103. It should work in a browser if you comment out the exports line.

License

Copyright (c) 2010, Ben Weaver <[email protected]> All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

• Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

• Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

• Neither the name of the nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.