Question

How do I generate a random GLfloat value in Haskell?

There is no instance declaration for Random GLfloat.

Answer 1

When there is no instance, make an instance. That’s the first thing they teach you.

There are many ways, but the easiest is probably to generate a type of sufficient resolution then cast that to a GLfloat:

instance Random GLfloat where
    random g = 
        let f :: Double
            (f,g2) = random g
        in (fromRational (toRational f), g2)

Double should suffice seeing as that’s a 64 bit floating value while GLFloat (which wraps CFloat) is a 32 bit float. Float should be sufficient, but I’m not well-versed enough in the specifics of Floating point to know for sure that this is true for all platforms.