Support `Gen.pick` by analogy to `Seq.pick`

Seq.pick is a very useful function that applies a given “chooser” function to successive elements, returning the first x where the function returns Some x. By analogy, I think FsCheck should provide a similar function. Here’s a simple implementation that demonstrates the idea:

let rec pick chooser gn =
    gen {
        let! value = gn
        match chooser value with
            | Some v -> return v
            | None -> return! pick chooser gn
    }

[ploeh]

That’s what I get for asking 😅 That’s not really in my wheelhouse, but in any case it’s hard to suggest alternatives without code.

[brianberns]

Sure. I’m working on a compiler that does type inferencing, which relies on a unification algorithm. Two types can be unified if there is a substitution that can be applied to both types to make them equal. My unit test generates pairs of types that can be unified and then verifies that the substitution does indeed produce equal types. I don’t know how to do this constructively (i.e. without filtering), but I’m certainly open to suggestions.