This post is part of a series of posts on implementing a minimal version of QuickCheck from scratch. The source code is available on GitHub.

In this post I’ll be generating random 32-bit floating-point numbers.

In Haskell’s QuickCheck 1.2.0.1 (but also in version 2.8), random 32-bit floating-point numbers are generated as shown below:

Two things are important in the above code:

Here’s the original `fraction` function in Haskell:

It takes 3 integers and returns an `a` which is a fractional (a numeric type that supports the ordinary division operator `/`).

Here are some sample values generated by fraction:

Now, what I want to do is to call the `fraction` function passing random integers, something like this (pseudo-code):

Here’s where `liftM3` comes into play:

• `a1`, `a2`, and `a3`, correspond to the arguments of `fraction`
• `r` corresponds to the return value of `fraction`
• `m a1`, `m a2`, `m a3` will be 3 generators for integers
• `m r` the return value (the random float).

So, in F#, a generator for floats can be written as:

And the `lift3` function in F# can be written in terms of `apply` and `return`:

Finally, here are some sample floats: