On 2008 Jul 5, at 19:02, Neil Mitchell wrote:

...

This is either a GHC bug, or a Yhc+Hugs bug - I'm not sure which, but the compilers disagree:

import Prelude hiding ((==)) data Foo = Foo instance Eq Foo where (==) a b = True

I was thinking that GHC's behaviour seems more sensible, but the following fails:

import qualified Module as M

instance MClass Foo where M.foo = undefined

M. is not allowed as a prefix of a function, which makes resolving ambiguities hard unless the compiler solves the issue for you (as Hugs and Yhc do)

But this works for me in ghc: foo.hs:

import Mod as M

data Bar a = Bar Int a

instance M.MClass (Bar a) where foo _ = M.foozero foozero = Bar 0 (undefined :: a)

main = putStrLn "foo"

Mod.hs:

module Mod where

class MClass a where foo :: a -> a foozero :: a

-- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH

I think GHC is right here. See http://haskell.org/onlinereport/decls.html#instance-decls esp the bit starting "It is illegal to give a binding..." Simon | -----Original Message----- | From: haskell-cafe-bounces@haskell.org [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of Neil | Mitchell | Sent: 06 July 2008 00:03 | To: Haskell Cafe | Subject: [Haskell-cafe] Re: Definition of hidden instance members (bug in GHC or Hugs+Yhc) | | > This is either a GHC bug, or a Yhc+Hugs bug - I'm not sure which, but | > the compilers disagree: | > | > import Prelude hiding ((==)) | > data Foo = Foo | > instance Eq Foo where | > (==) a b = True | | I was thinking that GHC's behaviour seems more sensible, but the | following fails: | | import qualified Module as M | | instance MClass Foo where | M.foo = undefined | | M. is not allowed as a prefix of a function, which makes resolving | ambiguities hard unless the compiler solves the issue for you (as Hugs | and Yhc do) | | Thanks | | Neil | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe@haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe