[Haskell-cafe] Polymorphic type
sarakenedy at gmail.com
Thu Jun 22 13:50:21 EDT 2006
Now I am trying with the function of polymorphic type: This function
returns the Nth element of list with type a. I try it as below.
getNthElem :: Int -> [a] -> Maybe a
getNthElemt _  = Nothing
getNthElem 0 _ = Nothing
getNthElem n s
| n > length s = Nothing
| otherwise = Just ((drop (n-1) (take n s))!!0)
>getNthElem 2 ["a","b","c"]
However, I do not satisfy with this function because I want to return
the Nth element of type a, not (Maybe a). For example, I want this
getNthElem :: Int -> [a] -> a
But, I do not know how to define the empty element of type a.
getNthElemt _  = ????
getNthElem 0 _ = ????
If you have some ideas about this, please give me some clues. Thanks a lot.
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