[Haskell-cafe] Just 3 >>= (1+)?

Brandon S. Allbery KF8NH allbery at ece.cmu.edu
Sat May 9 18:21:10 EDT 2009

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 at kf8nh.com
system administrator [openafs,heimdal,too many hats] allbery at ece.cmu.edu
electrical and computer engineering, carnegie mellon university    KF8NH

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