Source code in the fsharp programming language

let rec insert left x right = seq {
    match right with
    | [] -> yield left @ [x]
    | head :: tail -> 
        yield left @ [x] @ right
        yield! insert (left @ [head]) x tail
    }

let rec perms permute =
    seq {
        match permute with
        | [] -> yield []
        | head :: tail -> yield! Seq.collect (insert [] head) (perms tail)
    }
            
[<EntryPoint>]
let main argv = 
    perms (Seq.toList argv)
    |> Seq.iter (fun x -> printf "%A\n" x)
    0


let permutations xs = 
    let rec insert x = function
        | [] -> [[x]]
        | head :: tail -> (x :: (head :: tail)) :: (List.map (fun l -> head :: l) (insert x tail))
    List.fold (fun s e -> List.collect (insert e) s) [[]] xs