Here is a simple function to create Cartesian product sequence of tuples from x & y ranges. Nice for iterating 2d space:

module Seq =
    let public cartesianProduct xRange yRange = 
        seq {for y in yRange do
                for x in xRange do
                    yield (x,y) }

open System

Seq.cartesianProduct {0..3} {2..3}
|> Seq.iter (fun (x,y) -> Console.WriteLine("({0}, {1})", x, y))

Console.ReadKey() |> ignore

As an aside, looks like you cannot create type extensions for modules (Which is what I wanted to do for this function). Yeah, I know, it's "type" extensions not "module" extensions. The thing is though that F# modules compile down to public static classes; and you *can* create a type extension for System.Linq.Enumerable, which *is* a public static class. Doesn't seem consistent.