DEFINITION MODULE Stacks;

(*
 This module provides procedures for stack'ing objects up to 512 bytes in size.
 A stack may be made of non-homogeneous objects, but care muse be taken to pop
 data into the same format as there object which was push'ed.
 If an item longer than 512 bytes is pushed, then only the first 512 bytes is
 stored on the stack. And conversely, only as much data is pop'ed as can be
 stored in the object which will contain the pop'ed item.
*)
(* J. Andrea, Oct.3/91 *)
(* This code may be freely used and distributed, it may not be sold. *)

FROM SYSTEM IMPORT BYTE;

EXPORT QUALIFIED InitStack, Stack, Pop, Push, DelStack, StackInfo;

TYPE
   Stack; (* hidden *)

PROCEDURE InitStack( VAR a_stack :Stack );
(* Create a stack, this must be called before the first Push *)

PROCEDURE Push( a_stack :Stack; data :ARRAY OF BYTE );
(* Push an item onto the stack, any item up to 512 bytes in size *)

PROCEDURE Pop( a_stack :Stack; VAR data :ARRAY OF BYTE;
               VAR nothing_to_pop :BOOLEAN );
(* Pop the next item from the stack,
   return 'empty' as TRUE is there is nothing to get popped *)

PROCEDURE DelStack( VAR a_stack :Stack );
(* Delete the stack completely *)

PROCEDURE StackInfo( a_stack :Stack; VAR n_items, size :CARDINAL );
(* Get some information about the stack
   'n_items' is the number of items currently on the stack,
   'size'    is the size of the item at the top of the stack *)

END Stacks.