HP Understanding Prime Programming Language and Creating Efficient Prime Programs

Manipulating the stack

A number of stack-manipulation options are available. Most appear as menu items across the bottom the screen. To see these items, you must first select an item in history:

PICK

Copies the selected item to stack level 1. The item below the one

that is copied is then highlighted. Thus if you tapped four times, four consecutive items will be moved to the bottom four stack levels (levels 1–4).

ROLL

There are two roll commads:

•Tap to move the selected item to stack level 1. This is similar to PICK, but PICK duplicates the item, with the duplicate being placed on stack level1. However, ROLL doesn’t duplicate an item. It simply moves it.

•Tap to move the item on stack level 1 to the currently highlighted level

Swap	You can swap the position of the objects on stack level 1 with
	those on stack level 2. Just press o. The level of other objects
	remains unchanged. Note that the entry line must not be active
	at the time, otherwise a comma will be entered.
Stack	Tapping	displays further stack-manipulation tools.
DROPN	Deletes all items in the stack from the highlighted item down to
	and including the item on stack level 1. Items above the
	highlighted item drop down to fill the levels of the deleted items.

If you just want to delete a single item from the stack, see “Delete an item” below.

Reverse Polish Notation (RPN) 51