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

[Denis Bueno]

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