More F-algebra things in OCaml

FAlg.ml

module type Functor = sig
  type 'a t
  val map : ('a -> 'b) -> ('a t -> 'b t)
end

module Iso = struct
  type ('a, 'b) t = { fwd : 'a -> 'b; bck : 'b -> 'a }

  let fwd i = i.fwd
  let bck i = i.bck
end

module type FAlgebra = sig

  type t
  type 'a view

  module ViewFunctor : Functor with type 'a t = 'a view

  val project : t -> t view
  val embed   : t view -> t
  
end


module Fix (F : FAlgebra) = struct

  let rec cata (phi : 'a F.view -> 'a) (t : F.t) : 'a =
    phi (F.ViewFunctor.map (cata phi) (F.project t))

  let rec ana (psi : 'a -> 'a F.view) (a : 'a) : F.t =
    F.embed (F.ViewFunctor.map (ana psi) (psi a))
  
end