letrec loop = fun fcond -> fun fnext -> fun feval -> fun arg -> fun acc ->
              if ((fcond) arg) then acc
              else let iter = ((feval) arg) acc in
                   let next = (fnext) arg  in
                   ((((((loop) fcond) fnext) feval) next) iter)

in 
  let done = fun x -> (x = 0) in
  let next = fun x -> (x - 1) in
  let eval = fun x -> fun y -> x * y in
  ((((((loop) done) next) eval) 5) 1)