thachmai / clarsec

Parsec monadic parser ported to clojure

clarsec

clarsec is an attempt to port haskell parsec to clojure

This library is inspired on http://kotka.de/projects/clojure/parser.html and uses the Meikel Brandmeyer's "monad" library (slightly adapted), as I didn't understand how the clojure contrib monad library works.

Usage

there is an example parser which I ported straight from a Haskell Parsec code.

Basically, you should be able to write the examples on http://kotka.de/projects/clojure/parser.html.

The library comes with a small number of basic combinators. I hope it will be useful.

Caveats

forward references are a mess. I tried to maintain the DSL as simple as possible. Imagine that "structureDef" and "comma" are two already existing parsers, and "brackets" and "sepBy" are two combinators. I want to be able to write it like this:

(def structure (brackets (sepBy structureDef comma)))

however, clojures 'def' binding is strict and all the referenced vars have to be already defined, otherwise you get:

Var example/structureDef is unbound.

I'm a clojure newbie, so I don't know exactly how to avoid this. I know only of two workarounds:

1. use functions: (defn structure [] (brackets (sepBy (structureDef) (comma))))
2. use delay: (def structure (delay (brackets (sepBy structureDef comma))))

I opted for delay, as it allowed me to avoid all those spurious parens, and retain the illusion of a parser DSL, and put the "delay" only where needed. (or everywhere with a "defblabla" macro).

Unfortunately this required a small patch to Brandmeyer's monad library.

Installation

lein jar

License

http://www.apache.org/licenses/LICENSE-2.0.html