Saizan

module state =
  type StateM<'s,'a> = abstract Apply : 's  -> ('s -> 'a -> 'r) -> 'r

  let mkStateM (f : 's -> 's * 'a) : StateM<'s,'a> = 
     { new StateM< 's , 'a > with member __.Apply s k =  match f s with (s,a) -> k s a }

  let runStateM (m : StateM<'s,'a>) : 's -> 's * 'a = fun s ->
      m.Apply s (fun s a -> (s,a))

  // defined directly to avoid the value restriction.

Saizan

module tramp

// we want to use an existential type, but F# makes that complicated so obj it is.
type Tree = | Bind of Tree * (obj -> Tree)
            | Delay of (unit -> Tree)
            | Leaf of obj

type FnStack<'a,'b> = | End of ('a -> 'b) 
                      | Cons of ('a -> Tree) * FnStack<obj,'b>