# Peggy: A Parser Generator of Parsing Expression Grammer (PEG) #
# About
This is an yet another parser generator of Parsing Expression Grammer (PEG) which is:
* Simple
* Concise
* Fast
* Modern
# Usage
You can find a recent stable release in Hackage DB.
You can install this as following instruction:
~~~ {.bash}
$ cabal update
$ cabal install Peggy
~~~
# Why should you use Peggy?
Haskell has commonly used parser generators, one of them are Alex/Happy.
But I think Alex/Happy are not good in these points:
* Generates regacy codes
Alex uses only too basic libraries.
It does not use monad-transformers, iteratee, ListLike, Text, and so on.
* Tradisional Regexp/CFG based parser
Parsec has no good error recovery.
unnun, kannun...
...
# Quick Start
Here is an example of parsing arithmetic expressions.
~~~ {.haskell}
{-# QuasiQuotes #-}
{-# Language FlexibleContexts #-}
import Text.Peggy
[peggy|
exp :: Double
= exp "+" fact { $1 + $2 }
/ exp "-" fact { $1 - $2 }
/ fact
fact :: Double
= fact "*" term { $1 * $2 }
/ fact "/" term { $1 / $2 }
/ term
term :: Double
= "(" exp ")"
/ number
number ::: Double
= ([1-9][0-9]*) { read $1 }
|]
main :: IO ()
main =
print . parse exp =<< getContents
~~~