HP -28S Manual page 239

E' . .!AL
CU1F
Evaluate the outcome. In this example, EVAL
has no effect because the outcome is a string. In
a more realistic example, the outcome might be
a program (possibly stored in a variable), so
EVAL would be needed.
Enable the normal stack display.
When this sequence is executed, the user sees the option messages.
Pr-ess
[A] for- Apple
[B] for- Banana
[C] for- Cher-r-y
If the user presses a key other than
0,
[[j, or
W,
a beep sounds and
the error message appears for 1 second.
key
Then the option messages reappear. When the user presses
0,
[[j, or
W,
the string"
App
1 e",
"B.3n.3na",
or "Cher
t- ':I"
is returned to
level 1.
By modifying the list of possible outcomes, the option messages, and
the list of defined keys, you can make this sequence more significant
than putting a string on .the stack. More generally, by using local vari-
ables and putting this sequence inside a local-variable structure, you
can make the following program.
238 27: Interactive Programs
I