For example, if you search for `Integer -> Integer -> Integer` function, it will consider Integers of different bit-sizes. But if you instead search for `∀(n: Nat). Int(n) -> Int(n) -> Int(n)`, you will only consider integers of the same bit-size, which is a much smaller space. You can make arbitrary restrictions to shorten your search.

It works by enumerating ALL possible functions and running them. Obviously, that naive approach is exponential, so, the entire point is whether we can apply some clever tricks (based on optimal evaluators) to make this search "slightly less intractable".

So, to answer your question directly: if you asked it to design a prime number generator, if it found anything at all, it would probably be a simple, slow trial-and-error algorithm, or something in these lines.