Question

How can I get sqrt from Int.

I try so:

sqrt . fromInteger x

But get error with types compatibility.

Answer 1

Using fromIntegral:

Prelude> let x = 5::Int
Prelude> sqrt (fromIntegral  x)
2.23606797749979

both Int and Integer are instances of Integral:

• fromIntegral :: (Integral a, Num b) => a -> b takes your Int (which is an instance of Integral) and "makes" it a Num.

• sqrt :: (Floating a) => a -> a expects a Floating, and Floating inherit from Fractional, which inherits from Num, so you can safely pass to sqrt the result of fromIntegral

I think that the classes diagram in Haskell Wikibook is quite useful in this cases.