(*
    BSD 2-Clause License

    Copyright (c) 2018, Anton Krotov
    All rights reserved.
*)

MODULE COLLECTIONS;
                 

TYPE

    ITEM* = POINTER TO RECORD

        link: ITEM

    END;

    COLLECTION* = POINTER TO RECORD

        last: ITEM

    END;


PROCEDURE push* (collection: COLLECTION; item: ITEM);
BEGIN
    item.link := collection.last;
    collection.last := item
END push;


PROCEDURE pop* (collection: COLLECTION): ITEM;
VAR
    item: ITEM;

BEGIN
    item := collection.last;
    IF item # NIL THEN
        collection.last := item.link
    END

    RETURN item
END pop;


PROCEDURE create* (): COLLECTION;
VAR
    collection: COLLECTION;

BEGIN
    NEW(collection);
    collection.last := NIL

    RETURN collection
END create;


END COLLECTIONS.