[Haskell] Fundep broken in GHC 6.6
simonpj at microsoft.com
Wed Jan 3 11:09:07 EST 2007
[redirecting to ghc users]
Actually this didn't work in 6.4.2 either! (Though it did in 6.4, for reasons I have not investigated.)
Indeed I think your reasoning is correct. GHC tries to be pretty relaxed about reporting ambiguous types, which is what this amounts to really.
I have committed a fix to the HEAD that relaxes the condition, and allows this program. It should appear in 6.6.1 also.
Thanks for the report
| -----Original Message-----
| From: haskell-bounces at haskell.org [mailto:haskell-bounces at haskell.org]
| On Behalf Of dpus
| Sent: 12 November 2006 19:36
| To: haskell at haskell.org
| Subject: [Haskell] Fundep broken in GHC 6.6
| The following class declaration worked in GHC 6.4.
| I recently upgraded to 6.6 (following Debian), and
| now it is broken.
| class Error e => Game b mv e | b -> mv e where
| newBoard :: MonadState b m => m ()
| Since MonadState has the fundep m -> b, the type
| of newBoard fully specifies all of the class parameters.
| And this worked fine in GHC 6.4. But GHC 6.6
| The class method `newBoard'
| mentions none of the type variables of the class Game b mv e
| When checking the class method: newBoard :: m ()
| In the class declaration for `Game'
| Any ideas?
| Haskell mailing list
| Haskell at haskell.org
More information about the Glasgow-haskell-users