2-20 RPL Programming Examples
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9 `14 `
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Select the VAR menu and execute MNX2.
J %MNX2%
Find the minimum element.
%MIN%
Applying a Program to an Array
APLY!makes use of list processing to transform each element of an array according to a desired procedure. The
input array must be numeric, but the output array may be symbolic.!!
The procedure applied to each element must be a program that takes exactly one argument (i.e. the element) and
returns exactly one result (i.e. the transformed element).
Level 2 Level 1 " Level 1
[ array ] « program »
"
[[ array ]] or {{ array }}
Techniques used in APLY
! Manipulating Meta-Objects. Meta-objects are composite objects like arrays and lists that have been
disassembled on the stack. APLY illustrates several approaches to manipulating the elements and dimensions
of such objects.
! Application of List Processing. APLY makes use of DOSUBS (although DOLIST might also have been
used) to perform the actual transformation of array elements.
! Using an IFERR…THEN…ELSE…END Structure. The entire symbolic pseudo-array case is handled
within a error structure — triggered when the "ARRY command generates an error when symbolic elements
are present.
! Using Flags. User flag 1 is used to track the case when the input array is a vector.
APLY program listing
Program: Comments:
"!
!#!$!q!
!!"!
Store the array and program in local variables.
Begin the main local variable structure.
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