CODEWITHSUNDEEP
haskell
user3166747
user3166747

Reputation: 284

Type cast in Haskell

I know there is no "cast" in Haskell but I have this expression:

o = sum . takeWhile (< 10000) . filter odd . map (^2) $ [1..]

I would like to have the result as a Double. I tried:

g :: (Integral c, Double b) => [c] -> b
g =sum . takeWhile (< 10000) . filter odd . map (^2)

and other things like that... I always get an error. How can I do?

Upvotes: 1

Views: 3946

Answers (1)

Robert M. Lefkowitz
Robert M. Lefkowitz

Reputation: 1495

How about

g :: [Integer] -> Double
g = fromInteger . sum . takeWhile (< 10000) . filter odd . map (^2)

Or, you could convert the list to [Double] before the sum by 

g = sum . map fromInteger . takeWhile (< 10000) . filter odd . map (^2)

There is no generic cast in Haskell, but there are functions (like fromInteger and fromRational) which can convert from a particular type to a desired type. The type of fromIntegral is fromIntegral :: (Num b, Integral a) => a -> b It will convert an Integral value to any kind of Num value.

Upvotes: 4

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