[Haskell-cafe] Just 3 >>= (1+)?
Brandon S. Allbery KF8NH
allbery at ece.cmu.edu
Sat May 9 18:16:07 EDT 2009
On May 9, 2009, at 18:03 , Miguel Mitrofanov wrote:
> On 10 May 2009, at 00:30, Brandon S. Allbery KF8NH wrote:
>> On May 9, 2009, at 15:31 , michael rice wrote:
>>> Prelude> Just 3 >>= (1+)
>> That (a -> m b) in the middle is what's failing to typecheck. The
>> error is a bit obtuse because ghci is trying hard to find a way to
>> do what you want, so it assumes "m" is "(-> r)" (the functor/monad
>> representing functions, also known as the Reader monad)
> Ehm? What? I haven't seen the (-> r) monad anywhere near this code.
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.)
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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