I just applied this rule http://www.haskell.org/ghc/docs/latest/html/users_guide/type-extensions.html... In this case the type of newBoard is newBoard :: (Game b mv e, MonadStaet b m) => m () Following the rules in that manual section, this type sig is (now) ok. Does that answer your qn Simon | -----Original Message----- | From: sefer.org@gmail.com [mailto:sefer.org@gmail.com] On Behalf Of Yitzchak Gale | Sent: 03 January 2007 22:26 | To: Simon Peyton-Jones | Cc: GHC users | Subject: Re: [Haskell] Fundep broken in GHC 6.6 | | On 12 November 2006 I wrote (on the haskell list): | >> 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.... | >> But GHC 6.6 complains... | | Simon Peyton-Jones wrote: | > I have committed a fix to the HEAD that relaxes the | > condition, and allows this program. | > It should appear in 6.6.1 also. | | Thank you! | | Am I correct to assume that this fix only applies to the | specific case of unspecified class parameters in | method declarations? And not any of the other cases | where fundeps on class constraints resolve type ambiguity | but are ignored by GHC, such as instance declarations? | | Does the fix actually look at the fundeps in the class | constraint on the method, or just relax the | requirement that all class parameters be specified in | every method? If it is the latter, as I suspect, then is | the requirement always relaxed, or only when there is | a class constraint on the method? | | Thanks, | Yitz