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haskelltypescastinginteger

Haskell Convert Integer to Int?

Is it possible to cast an Integer to an Int? The other direction is possible: toInteger. I know that Integer is able to store bigger values, but sometimes a conversation is needed to use functions in the standard library. I tried (n :: Int) and other code samples I found - but nothing works.

takeN :: Integer -> [a] -> [a]
takeN n l = take n l
Solution

  • Use fromIntegral.

    takeN :: Integer -> [a] -> [a]
takeN n l = take (fromIntegral n) l

    Note that fromIntegral :: (Integral a, Num b) => a -> b, so sometimes you will need an extra type annotation (e.g. (fromIntegral n :: Int)), but usually the compiler can infer which type you want.

    In the special case of your example, in Data.List there is genericTake :: (Integral i) => i -> [a] -> [a], which does the same thing as take but with a more general type.