This bad error message is improved in subsequent versions of GHC. 6.0.1 says In.hs:5: Duplicate instance declarations: In.hs:5: Functor ((->) i) In module Control.Monad.Reader: Functor ((->) r) Simon | -----Original Message----- | From: haskell-bounces@haskell.org [mailto:haskell-bounces@haskell.org] On Behalf Of Frieder Kalisch | Sent: 01 October 2003 15:12 | To: haskell@haskell.org | Subject: Imported instance declarations | | Hello, | | While trying to learn Hakell I came across a weird (to me) error message | concerning imported instance declarations. | | This module | | module XXX() where | | import Control.Monad.Error() | | instance Functor ((->)i) where | fmap = (.) | | gives this error message (compiling with ghc 5.0.4.2): | | Duplicate instance declarations: | XXX.hs:5: Functor ((->) i) | <No locn>: Functor ((->) r) | | For me this error message is somewhat puzzling: Where is the second | instance declaration given? In this case it happens to be in | Control.Monad.Reader, but how can I find out without looking for it | in the CVS repository? The documentation for Control.Monad.Error does | not mention the imported modules. | | I suppose, that the compiler knows in which module the instance | declaration was given, because it needs to tell duplicate import paths | from duplicate instance declarations. Why is it not given in this example? | | Greetings | | Frieder Kalisch | | | -- | Frieder Kalisch | f.kalisch@tphys.uni-heidelberg.de | +49-6221-549-432 | | _______________________________________________ | Haskell mailing list | Haskell@haskell.org | http://www.haskell.org/mailman/listinfo/haskell