array permutations

permute.fs

let permute (a: 'a array) =
    let swap a i j = Array.permute (fun idx -> if idx = i then j else if idx = j then i else idx) a
    let rec p a i = seq {
        if i >= Array.length a then yield a
        else for j=i to a.Length-1 do yield! p (swap a i j) (i + 1) }
    p a 0