Stack and Queue functions (LIFO and FIFO)

[Peter-Jacob]

By leveraging the linked list implementation, we can easily implement stack functionality on top of it. The stack operates as a standard stack, without additional behavior like waiting for input from the keyboard or other input sources. The cherry on top? It supports several parallel stacks—because one just isn’t enough.
I almost overlooked the most obvious approach: encapsulating the functionality in REXX.
For example, to PULL data from the stack, I use the following REXX code:

pull: procedure = .string
  arg llist = .int               ## linked-list number
  call setNode llist,"LAST"      ## set pointer to last added entry
  record=currentNode(llist)      ## retrieve it
  call removeNode(llist)         ## remove the entry   
return record                    ## return entry 

This eliminates the need to write additional code in the plugin.

These are the functions we have so far:

PUSH(queue-number, data) pushes the data onto the stack's top.
QUEUE(queue-number, data) adds the data to the beginning of the stack.
PULL(queue-number) retrieves and removes the topmost entry from the stack.
QPULL(queue-number) returns the first entry from the stack and removes it. (I never understood why it isn't part of the standard)