Reference Guide
RPL Programming 1-13
Testing Object Types
The TYPE command (!°
%TEST%
L
%TYPE%
) takes any object as its argument and returns the number that
identifies that object type. For example,
"HELLO" TYPE
returns 2, the value for a string object. See the table of
object types in chapter 3, in the TYPE command, to find calculator objects and their corresponding type numbers.
Testing Linear Structure
The LININ command (!°
%TEST%
!«
%LININ%
) takes an algebraic equation on level 2 and a variable
on level 1 as arguments and returns 1. if the equation is linear for that variable, or 0. if it is not. For example,
'H+Y^2' 'H' LININ
returns 1. because the equation is structurally linear for H. See the LININ command in
chapter 3 for more information.
Using Conditional Structures and Commands
Conditional structures let a program make a decision based on the results of tests.
Conditional commands let you execute a true-clause or a false-clause (each of which are a single command or object).
These conditional structures and commands are contained in the PRG BRCH menu (!°
%BRCH%
):
IF … THEN … END structure.
IF … THEN … ELSE … END structure.
CASE … END structure.
IFT (if-then) command.
IFTE (if-then-else) function.
The IF THEN END Structure
The syntax for this structure is
«
…
IF
test-clause
THEN
true-clause
END
…
»
IF … THEN … END executes the sequence of commands in the true-clause only if the test-clause evaluates to true.
The test-clause can be a command sequence (for example,
A B ‰
) or an algebraic (for example,
'A‰B'
). If the
test-clause is an algebraic, it’s automatically evaluated to a number — you don’t need →NUM or EVAL.
IF begins the test-clause, which leaves a test result on the stack. THEN removes the test result from the stack. If the
value is nonzero, the true-clause is executed — otherwise, program execution resumes following END. See
“Conditional Examples” on page 1-15.
To enter IF THEN END in a program:
Press
!°%BRCH%
!%IF%
.
The IFT Command
The IFT command takes two arguments: a test-result in level 2 and a true-clause object in level 1. If the test-result is
true, the true-clause object is executed — otherwise, the two arguments are removed from the stack. See
“Conditional Examples” on page 1-15.
To enter IFT in a program:
Press
!°%BRCH%
L!%IFT%
.
The IF THEN ELSE END Structure
The syntax for this structure is