iter.ml

module Iter = struct
  type 'a t = {
    fold: 'b. ('b -> 'a -> 'b) -> 'b -> 'b
  }

  let empty = {
    fold = fun f accu -> accu
  }

  let pure a = {
    fold = fun f accu -> f accu a
  }

  let fold f a b = b.fold f a

  let append a b = {
    fold = fun f accu -> fold f (fold f accu a) b
  }

  let map f a = {
    fold = fun g accu -> fold (fun accu a -> g accu (f a)) accu a
  }

  let bind f a = {
    fold = fun g accu -> fold (fun accu a -> fold g accu (f a)) accu a
  }

  let ap f a = {
    fold = fun g accu -> fold (fun accu f -> fold g accu (map f a)) accu f
  }
end