(* buffer.sml *)

(* CML buffers of length at most one *)

structure Buffer :> BUFFER =
struct

open CML

type 'a buffer =
       {addCh  : 'a chan,  (* values sent to this channel will be added to
                              buffer *)
        delCh  : 'a chan}  (* values read from this channel will be deleted
                              from buffer *)

(* val server : 'a buffer -> 'b *)

fun server{addCh, delCh} =
      let (* val empty : unit -> 'b *)

          fun empty() = full(recv addCh)

          (* val full : 'a -> 'b *)

          and full x = (send(delCh, x); empty())
      in empty() end

fun make() =
      let val buf = {addCh  = channel(), delCh  = channel()}
      in spawn(fn () => server buf); buf end

fun add({addCh, ...} : 'a buffer, x) = send(addCh, x)

fun del({delCh, ...} : 'a buffer) = recv delCh

end;