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