22 Dec
2008
22 Dec
'08
9:17 a.m.
2008/12/22 Andrew Wagner
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