[Haskell-beginners] Re: Function composition with more than 1 parameter

[Daniel Fischer]

Am Samstag, 25. Oktober 2008 12:34 schrieb Glurk:
> > The lambdabot on #haskell has a plugin named "pointless" that can
> > transform this into a definition that doesn't mention  x  and  xs
> > anymore. I think it will propose
> >
> >   howMany = (length .) . matches
> >
> > And with
> >
> >   matches x xs = filter (x==) xs
> >
> >   matches x    = filter (x==)
> >
> >   matches      = filter . (==)
> >
> > we have
> >
> >   howMany = (length .) . filter . (==)
> >
> >
> >   howMany = curry (length . uncurry matches)
>
> Thanks apfelmus,
>
> unfortunately, none of those suggested changes seem to work !
> I get errors like :-
>
> Unresolved top-level overloading
> *** Binding             : howMany2
> *** Outstanding context : Eq b
>
> I'm using WinHugs - do you get them to work in some other environment ?

Did you give a type signature for these?
Then you would of course have to include the context Eq b, since (==) is used.
If you don't give any type signatures, all above versions should work in all 
environments, otherwise it would be a serious bug.
>
> Thanks ! :)
>