How does type casting work in Haskell?

Question

I want to be able to be able to truncate a float or double in a similar way you would in Java: (int)5.583, for example.

I've done some research and, to my knowledge, there's nothing imported in Prelude for this. So I'm wondering how I would construct a function that does it. I thought maybe if I did show 5.583 and then took a substring up to the decimal point and then converted that to an Int, but that seems like it would be terribly inefficient when using only recursion. So is there a more simple way to go about it?

Answer 1

I want to be able to be able to truncate float or double

Delightfully, the function that truncates fractionals to integrals is named "truncate".

https://www.stackage.org/haddock/lts-8.4/base-4.9.1.0/Prelude.html#v:truncate

λ> truncate 5.583
5

Its type is

truncate :: (Real a, Fractional a, Integral b) => a -> b

This is just an ordinary function. Haskell does not have any language feature (or kludge, if you will) akin to type casting in Java.

Answer 2

Converting floating point numbers with ghc is possible with:

λ> :m GHC.Float
λ> :t float2Double
float2Double :: Float -> Double
λ> :t double2Float
double2Float :: Double -> Float
λ> :t double2Int
double2Int :: Double -> Int
λ> :t float2Int
float2Int :: Float -> Int
λ> :t int2Double
int2Double :: Int -> Double
λ> :t int2Float
int2Float :: Int -> Float

But for floating point numbers to ints I'd recommend using ceiling, round and floor, and fromIntegral for backwads conversion.

Edit: after reading the question more carefully, @Chris Martin's answer is the correct one:

λ> :t truncate
truncate :: (Integral b, RealFrac a) => a -> b