[Chapter 5] 5.24 PLVstk: Stack Manager Chapter 5PL/Vision Package Specifications 5.24 PLVstk: Stack ManagerThe PLVstk (PL/Vision STacK manager) package is a generic manager for both first-in-first-out (FIFO) and last-in-last-out (LIFO) stacks; it is built on PLVlst. See the companion disk for details.5.24.1 Package constants defstk CONSTANT VARCHAR2(5) := 'stack';The name of the default stack. lifo CONSTANT VARCHAR2(4) := 'LIFO';Indicates that you are working with a last-in-first-out stack. Used in calls to pop. fifo CONSTANT VARCHAR2(4) := 'FIFO';Indicates that you are working with a first-in-first-out stack. Used in calls to pop.5.24.2 Creating and destroying stacks PROCEDURE make (stack_in IN VARCHAR2 := defstk, overwrite_in IN BOOLEAN := TRUE);Allocates storage for a stack of up to 1,000 items with the specified name. By default, if the stack already exists it will be reinitialized to an empty stack. PROCEDURE destroy (stack_in IN VARCHAR2 := defstk);Releases all memory associated with this stack.5.24.3 Modifying stack contents PROCEDURE push (item_in IN VARCHAR2, stack_in IN VARCHAR2 := defstk);Pushes an item onto the specified stack. PROCEDURE pop (value_out IN OUT VARCHAR2, stack_in IN VARCHAR2 := defstk, stack_type_in IN VARCHAR2 := lifo);Pops an item off the top (LIFO) or bottom (FIFO) of the stack.5.24.4 Analyzing stack contents FUNCTION nitems (stack_in IN VARCHAR2 := defstk)RETURN INTEGER;Returns the number of items currently in the stack. FUNCTION itemin (stack_in IN VARCHAR2, item_in IN VARCHAR2)RETURN BOOLEAN;Returns TRUE if the specified item is found in the stack.5.24.5 Tracing Stack Activity PROCEDURE show (stack_in IN VARCHAR2 := defstk, show_contents_in IN BOOLEAN := FALSE);Requests that pre-action status of stack be displayed for the specified stack (or all). PROCEDURE noshow;Turns off display of pre-action status. FUNCTION showing RETURN BOOLEAN;Returns TRUE if showing pre-action status. PROCEDURE verify (stack_in IN VARCHAR2 := defstk, show_contents_in IN BOOLEAN := FALSE);Requests that post-action status of stack be displayed for the specified stack (or all). PROCEDURE noverify;Turns off display of post-action status. FUNCTION verifying RETURN BOOLEAN;Returns TRUE if showing post-action status.5.23 PLVrb: Rollback Processing5.25 PLVtab: Table Interface Copyright (c) 2000 O'Reilly & Associates. All rights reserved.