Arrow.ml

module Action : sig
  type _ t

  val execute : 'a t -> 'a

  val readFile : string -> string t

  val writeFile : string -> string -> unit t
end = struct
  type _ t =
    | ReadFile : string -> string t
    | WriteFile : string * string -> unit t

  let readFile f = ReadFile f

  let writeFile f data = WriteFile (f, data)

  let execute : type res. res t -> res = function
    | ReadFile f ->
        let ic = open_in f in
        let rec read acc =
          try
            let acc = input_line ic :: acc in
            read acc
          with End_of_file -> acc
        in
        let data = read [] in
        close_in ic ; String.concat "\n" data
    | WriteFile (f, data) ->
        let oc = open_out f in
        Printf.fprintf oc "%s\n" data ;
        close_out oc
end