How do I convert a -> Float?

Question

I think that I could use fromEnum for a -> Int but how do I do it for a -> Float. I need my variable to be a Float for my function to work but I can't work out how to convert it? I've gone through the Prelude and can't see anything that would work. Sorry if this is a really stupid question but I'm just starting out.

Answer 1

It depends on what a is. If a is an instance of Integral, like Int or Integer, you can use

fromIntegral :: (Integral a, Num b) => a -> b

If a is an instance of Real, like Rational or Double, you can use

realToFrac :: (Real a, Fractional b) => a -> b

There are also special functions for Integer and Rational that fromIntegral and realToFrac are based on:

fromInteger :: (Num a) => Integer -> a
fromRational :: (Fractional a) => Rational -> a

If a is an instance of Enum (and so you can use fromEnum, as you said), then fromIntegral . fromEnum should do it. fromEnum converts a to Int, then fromIntegral converts from Int to Float, so fromIntegral . fromEnum converts a to Float.

Answer 2

You can convert an (Enum a) => a to an Int first, and then the Int to a Float. To convert an Int to a Float (or many other number types), you use fromIntegral. A function that combines these two functions would be:

floatFromEnum :: (Enum a) => a -> Float
floatFromEnum = fromIntegral . fromEnum 

EDIT: Note that fromEnum doesn't work for any a, as you are implying, but only works for a's that are Enum instances.