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

Denis Bueno dbueno at gmail.com
Mon Dec 22 09:17:25 EST 2008

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


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