On 5 April 2015 at 22:25, Roman Cheplyaka
Data.ByteString.Lazy.Char8 exports the same lazy bytestring type as Data.ByteString.Lazy. Only functions and instances differ.
Well, *instances* can't differ...
On 05/04/15 15:19, Daniel Trstenjak wrote:
Hi,
I'm getting the compile error:
Gamgine/Image/PNG/Internal/Parser.hs:14:10: Functional dependencies conflict between instance declarations: instance Monad m => Stream LB.ByteString m Word8 -- Defined at Gamgine/Image/PNG/Internal/Parser.hs:14:10 instance Monad m => Stream LB.ByteString m Char -- Defined in ‘Text.Parsec.Prim’
The relevant stuff from the parsec 3.1.9 code[1] is:
{-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies, FlexibleContexts, UndecidableInstances #-}
...
import qualified Data.ByteString.Lazy.Char8 as CL import qualified Data.ByteString.Char8 as C
...
class (Monad m) => Stream s m t | s -> t where uncons :: s -> m (Maybe (t,s))
instance (Monad m) => Stream CL.ByteString m Char where uncons = return . CL.uncons
instance (Monad m) => Stream C.ByteString m Char where uncons = return . C.uncons
And from my code[2] is:
{-# LANGUAGE BangPatterns, FlexibleInstances, MultiParamTypeClasses, FlexibleContexts #-}
...
import qualified Data.ByteString.Lazy as LB
...
instance (Monad m) => Stream LB.ByteString m Word8 where uncons = return . LB.uncons
As you can see, the instances are for different ByteString types, therefore I don't quite get where GHC sees here any conflicts.
Greetings, Daniel
[1] https://github.com/aslatter/parsec/blob/master/Text/Parsec/Prim.hs [2] https://github.com/dan-t/Gamgine/blob/master/Gamgine/Image/PNG/Internal/Pars... _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
-- Ivan Lazar Miljenovic Ivan.Miljenovic@gmail.com http://IvanMiljenovic.wordpress.com