Solution to Paul Grahams accumulator generator problem, for OCaml.. http://www.paulgraham.com/accgen.html

accgen.ml

module Num = struct

  type t = [ `F of float | `I of int ]

  let to_float = function
      `F f -> f
    | `I i -> float i

  let add n n' = match n, n' with
      `F f, `F f' -> `F (f +. f')
    | `I i, `I i' -> `F (float (i + i'))
    | `F f, `I i | `I i, `F f  -> `F ((float i) +. f)

  let accgen n =
    let r = ref n in fun i -> r := add !r i; !r

end