haskell - Typechecking problems with pipes-attoparsec -

i've been trying out pipes-attoparsec haven't been having luck.

it appears there type mismatch between void , x in (what seems be) relatively straightforward code. i've read in library (that type synonym @ point), i'm not sure how interpret type error.

test code:

{-# language overloadedstrings,rankntypes #-} module main  import qualified data.attoparsec.char8  import qualified pipes p import qualified pipes.attoparsec pa         import qualified pipes.bytestring pb import qualified pipes.parse  pp  passthrough :: a.parser pb.bytestring passthrough = a.takewhile (\s->true)  f :: monad m => pp.statet (p.producer pb.bytestring m r) m (either string  string) f =   r <- pa.parse passthrough   return $ case r of     left e -> left "a"     right (_,r1) -> right "b"  g = pp.evalstatet f pb.stdin  h = p.runeffect g 

this results in error:

p.hs:16:8:     couldn't match type `pipes-4.0.2:pipes.internal.proxy                            data.void.void () () pb.bytestring m r0'                   `p.proxy p.x () () pb.bytestring m r'     expected type: pp.statet                      (pp.producer pb.bytestring m r)                      m                      (either pa.parsingerror (int, pb.bytestring))       actual type: pp.statet                      (pipes-4.0.2:pipes.core.producer pb.bytestring m r0)                      m                      (either pa.parsingerror (int, pb.bytestring))     in return type of call of `pa.parse'     in stmt of 'do' block: r <- pa.parse passthrough     in expression:       { r <- pa.parse passthrough;            return            $ case r of {                left e -> left "a"                right (_, r1) -> right "b" } } failed, modules loaded: none. 

you need upgrade latest pipes-attoparsec, restricts pipes dependency 4.1.*. can give more detailed information how might have arisen if list versions have installed pipes, pipes-parse, , pipes-attoparsec. if type ghc-pkg list | grep pipes should enough.