CHANGESTR.REX
the CHANGESTR function
This a RYO version of the REXX function changestr (change <c>string).
It is included in some of the more modern Classic REXXes, but older versions of
Classic REXX don't have this function as a BIF (built-i function).
This version of the changestr BIF has more functionality than the standard BIF.
the CHANGESTR source
<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: 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 /*5th arg " " " */ if t<0 then signal syntax /*4th arg not non-negative*/ if b<1 then signal syntax /*5th arg not 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? */ if p\=1 then do /*if P ¬= 1, adjust 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.*/ 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 end /*j*/ /*Note: most REXX ··· */ /* CHANGESTR BIFs only ···*/ return f || $ || h /* support three options. */</lang>