[Haskell-beginners] Re: [Haskell-cafe] Defining a containing function on polymorphic list

[Andrew Wagner]

Yes, of course, sorry for the typo.

On Mon, Dec 22, 2008 at 9:17 AM, Denis Bueno <dbueno at gmail.com> wrote:

> 2008/12/22 Andrew Wagner <wagner.andrew at gmail.com>:
> > The problem here is even slightly deeper than you might realize. For
> > example, what if you have a list of functions. How do you compare two
> > functions to each other to see if they're equal? There is no good way
> really
> > to do it! So, not only is == not completely polymorphic, but it CAN'T be.
> >
> > There is a nice solution for this, however, and it's very simple:
> >
> > contain :: Eq a -> [a] -> Bool
>
> Please note that the syntax here should be:
>
>    contain :: Eq a => a -> [a] -> Bool
>
>                              Denis
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.haskell.org/pipermail/beginners/attachments/20081222/bf05cd3c/attachment.htm