On May 9, 2009, at 18:16 , Brandon S. Allbery KF8NH wrote:
That's the only way I can get the error he got; if it uses Maybe as the monad then why is the Maybe on the *inside* in the error message? Clearly it bound m to something else, and ((->) r) is the only other one I can think of applying there. (Hm, I suppose it could be IO forced by the ghci context, but I didn't think it worked that way.)
Er, clarifying: it's looking for Num (Maybe a), but the context where Num applies is inside the scope where the Maybe applies (a -> m b has been fixed at Num n => n -> m n). But the error message says ghc is trying to make *n* an instance of Num. -- 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