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[[Category:REXX_library_routines]]
== the CHANGESTR function ==
This a RYO version of the REXX function '''changestr''' (<u>change</u> <u>str</u>ing).
It is included in some of the more modern Classic REXXes, but older versions of
<br>Classic REXX don't have this function as a BIF (<u>B</u>uilt-<u>I</u>n-<u>F</u>unction).
This version of the '''changestr''' BIF has more functionality than the standard BIF.
__TOC__
===the CHANGESTR (external) program source===
The following CHANGESTR program can be coded as is when the intention is to be an external routine (function).
<lang rexx>/*REXX program emulates the CHANGESTR BIF (built-in function) for older REXXes.*/
/*──────────── This version has more functionality: limit the number of changes. */
/*──────────── start of change occurrence#. */
/*──────────── start of change position. */
/* ╔═══════════════════════════ CHANGESTR function ════════════════════════╗
╔═╩═══════════════════════════════════════════════════════════════════════╩═╗
║ The CHANGESTR function is used to replace some or all occurrences of an ║
║ (old) string in a haystack with a new string. The changed string is ║
║ original haystack is returned. If the old string is a null string, ║
║ then the original string is prefixed with the new string.
║ new string to be used ►──────┐ ┌──────◄ limit of # changes (times).║
║ original string (haystack) ►────┐ │ │ [default: ≈ one billion] ║
║ old string to be replaced ►──┐ │ │ │ ┌────◄ begin at this occurrence # ║
║ {O, H, and N can be null.} │ │ │ │ │ ┌──◄ start position (default=1) ║
╚═╦═════════════════════════════╗ │ │ │ │ │ │ ╔═══════════════════════════╦═╝
╚═════════════════════════════╝ │ │ │ │ │ │ ╚═══════════════════════════╝
if
if
if \datatype(p, 'W')
if p\=1 then do
end /*now, proceed as usual. */
do j=1 while # <
if _=='' then return f || $ || y /*no more left, return. */
$=$ || y /*append the residual txt.*/
/* [↓] check if too soon.*/
if j<b then $=$ || o /*append OLD if too soon. */
else do /*met the occurrence test.*/
$=$ || n /*append the NEW string.*/
#=#+1 /*bump occurrence number. */
end /* [↑] append new string.*/
end /*j*/ /*Note: most REXX ··· */
/* CHANGESTR BIFs only ···*/
return f || $ || h /* support three options. */</lang>
=== the CHANGESTR (internal) procedure source ===
The following CHANGESTR program can be coded as is when the intention is to be an internal routine (function).
Only the '''changestr:''' statement is changed (by adding a '''procedure''' to the label).
<lang rexx>/*REXX program emulates the CHANGESTR BIF (built-in function) for older REXXes.*/
/*──────────── This version has more functionality: limit the number of changes. */
/*──────────── start of change occurrence#. */
/*──────────── start of change position. */
/* ╔═══════════════════════════ CHANGESTR function ════════════════════════╗
╔═╩═══════════════════════════════════════════════════════════════════════╩═╗
║ The CHANGESTR function is used to replace some or all occurrences of an ║
║ (old) string in a haystack with a new string. The changed string is ║
║ returned. If the haystack doesn't contain the old string, the ║
║ original haystack is returned. If the old string is a null string, ║
║ then the original string is prefixed with the new string. ║
║ ║
║ new string to be used ►──────┐ ┌──────◄ limit of # changes (times).║
║ original string (haystack) ►────┐ │ │ [default: ≈ one billion] ║
║ old string to be replaced ►──┐ │ │ │ ┌────◄ begin at this occurrence # ║
║ {O, H, and N can be null.} │ │ │ │ │ ┌──◄ start position (default=1) ║
╚═╦═════════════════════════════╗ │ │ │ │ │ │ ╔═══════════════════════════╦═╝
╚═════════════════════════════╝ │ │ │ │ │ │ ╚═══════════════════════════╝
↓ ↓ ↓ ↓ ↓ ↓ */
changestr: procedure; parse arg o,h,n,t,b,p, ,$ f /* ◄────────────────────┐*/
/*T, B, P are optional ►─┘*/
t=word(t 999999999, 1) /*maybe use the default? */
b=word(b 1 , 1) /* " " " " */
p=word(p 1 , 1) /* " " " " */
if arg() < 3 then signal syntax /*not enough arguments. */
if arg() > 6 then signal syntax /*too many arguments. */
if \datatype(t, 'W') then signal syntax /*4th arg not an integer. */
if \datatype(b, 'W') then signal syntax /*5th " " " " */
if \datatype(p, 'W') then signal syntax /*6th " " " " */
if t<0 then signal syntax /*4th " " non-negative.*/
if b<1 then signal syntax /*5th " " positive. */
if p<1 then signal syntax /*6th " " " */
L=length(o) /*length of OLD string. */
if L==0 & t\=0 then return n || h /*changing a [null] char? */
/* [↓] check for position*/
if p\=1 then do /*P¬=1? Then ajust F & H.*/
f=left(h, min(p-1, length(h))) /*keep first part intact. */
h=substr(h, p) /*only use this part of H.*/
end /*now, proceed as usual. */
#=0 /*# of changed occurrences*/
do j=1 while # < t /*keep changing, T times. */
parse var h y (o) _ +(L) h /*parse the haystack ··· */
if _=='' then return f || $ || y /*no more left, return. */
$=$ || y /*append the residual txt.*/
/* [↓] check if too soon.*/
if j<b then $=$ || o /*append OLD if too soon. */
else do /*met the occurrence test.*/
$=$ || n /*append the NEW string.*/
#=#+1 /*bump occurrence number. */
end /* [↑] append new string.*/
end /*j*/ /*Note: most REXX ··· */
/* CHANGESTR BIFs only ···*/
return f || $ || h /* support three options. */</lang>
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