[Haskell-cafe] Iteratee, parsec & co.

Maciej Piechotka uzytkownik2 at gmail.com
Tue Feb 9 04:03:46 EST 2010

I read a lot about iteratee IO and it seemed very interesting
(Unfortunately it lacks tutorial). Especially features like 'no input
yet' in network programming (with lazy IO + parsec I run into problems
as it tried to evaluate the first response character before sending

I decided first write a simple program and then attempt write a Stream
implementation for parsec.

> {-# LANGUAGE FlexibleInstances #-}
> {-# LANGUAGE MultiParamTypeClasses #-}
> import Data.Iteratee
> import Text.Parse
> data Buffer a = Buffer
> instance Monad m => Stream (Buffer a) (IterateeG [] a m) a where
>     uncons Buffer = IterateeG loop
>                     where loop (Chunk [])     =
>                               return $! Cont (IterateeG loop) Nothing
>                           loop (Chunk (x:xs)) =
>                               return $! Done (Just (x, Buffer))
>                                              (Chunk xs)
>                           loop (EOF Nothing)  =
>                               return $! Done Nothing (EOF Nothing)
>                           loop (EOF (Just e)) =
>                               return $! throwErr e

1. I'm not quite sure what Cursor was suppose to do from A Parsing
Trifecta presentation.

2. Is there any package which contains this stream definition?

3. Why Seek FileOffset is error message?


PS. I guess iteratee does qualify as cafe but if beginner would be more
appropriate group then I'm sorry - I'll remember next time.
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