(* the signature is restricting the types of the concreteFunction structure *)

signature int_bool_function = sig
	val f1 : int * bool list -> (int * bool) list
end;

structure abstractFunction = struct
	fun f1 (i, nil) = nil
	| f1 (i, c::cs) = (i, c) :: f1(i, cs);
end;


structure concreteFunction:int_bool_function = abstractFunction;