DEFINITION PrintableObjects

(*
 *	Entwicklung objekt-orientierter Bibliotheken, Aufgabe 16
 *
 *	Abstraktion PrintableObjects aus der Vorlesung.
 *)
DEFINITION PrintableObjects;

   IMPORT Services, Streams;

   (* secondary abstraction for printable objects
      which is usually to be supported by type-dependent modules
   *)

   TYPE
      PrintProc = PROCEDURE (s: Streams.Stream; object: Services.Object);

   PROCEDURE Support(for: Services.Type; print: PrintProc);
      (* supply print method for all instances of `for' and its extensions *)

   PROCEDURE SetDefault(s: Streams.Stream; default: ARRAY OF CHAR);
      (* sets the per-stream default output text for objects
         which do not have an associated print method
      *)

   PROCEDURE Print(s: Streams.Stream; object: Services.Object);
      (* call the print method of `object', or, if not present,
         the per-stream default text, or, if not present, a question mark
      *)

END PrintableObjects.