manual:chapter6:stack:cmd_stkdrop [newRPL User Manual]

Synopsis

Drop a snapshot from the top of the Undo stack

Stack Diagram

Input Stack		Output Stack
	→
Level 1	→	Level 1

Legend

Legend	Object type
O	Any object
I	Integer number
R	Real number
#	Binary number
Num	Scalar (Integer, Real or Binary number)
Z	Complex number
U	Unit
∡	Angle
A	Symbolic expression
C	Symbolic constant
V	Vector
M	Matrix
S	String
1/0	Any expression evaluating to True or False
G	Grob
F	Font
D	Binary data container
T	Tag object
L	List
cL	Case list
N	Variable name / Identifier
Dir	Directory
pDir	Packed Directory
P	Program
Lib	Library

Type	Command
Parallel list processing	Group 1
Affected by flags	None

Description

The STKDROP command deletes the snapshot on the top of the Undo stack and subsequently all remaining snapshots drop one place.

The command has little utility in interactive mode, because before STKDROP is executed a snapshot of the stack is pushed on the Undo stack: the only effect of STKDROP would be to delete the copy that was just made, leaving the Undo stack unchanged (except for the fact that its level 8 would have been lost in the process).

Compatibility

This command is new in newRPL and does not exist in userRPL.

Usage

The following program

« "ABC"
  STKPUSH
  CLEAR
  123
  456
  789
  STKPUSH
  CLEAR
  999
  STKDROP
  STKPOP
»

creates the following stack (before STKDROP is executed)

1:                           999
……………………………………………………………………………………

The effect of STKPOP is to replace it with

 
1:                         "ABC"
……………………………………………………………………………………

Related Commands

Stack manipulation 27 5 NEW

Command	Short Description
CLEAR	Remove all objects from the stack
DEPTH	Get the current stack depth
DROP	Remove an object from the stack
DROP2	Remove two objects form the stack
DROPN	Remove N objects from the stack
DUP	Duplicate an object on the stack
DUP2	Duplicate two objects on the stack
DUPDUP	Duplicate the same object twice on the stack
DUPN	Duplicate a group of N objects
NDUPN	Replicate one object N times and return N
NIP	Remove object at level 2 on the stack
OVER	Duplicate object at level 2 on the stack
PICK	Duplicate object at position N on the stack
PICK3	Duplicate object at level 3 on the stack
ROLL	Move object at level N to level 1
ROLLD	Move object from level 1 to level N
ROT	Move object from level 3 to level 1
SWAP	Exchange objects in levels 1 and 2
UNPICK	Move object from level 1 to level N.
UNROT	Move object from level 1 to level 3
IFT	Evaluate objects on the stack conditionally
IFTE	Evaluate objects on the stack conditionally
STKPUSH	Push a snapshot of the current stack on the undo stack	NEW
STKPOP	Pop a stack snapshot from the undo stack	NEW
STKDROP	Drop a snapshot from the undo stack	NEW
STKPICK	Copy snapshot in level N to the current stack	NEW
STKDEPTH	Get the depth of the undo stack	NEW