(* primes.sig *)

(* generation of primes *)

signature PRIMES =
sig

(* the following sequence of declarations produces all the primes:

   val (pr1, st) = next init
   val (pr2, st) = next st
   val (pr3, st) = next st
   ...
*)

type state

val init : state  (* initial state *)

val next : state -> int * state  (* state transition, yielding prime *)

end;