CHANGESTR.REX

This a RYO version of the REXX function   changestr   (CHANGE 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-In Function).

This version of the   changestr   BIF has more functionality than the standard BIF.

<lang rexx>/*REXX program emulates the CHANGESTR 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.  */

1. =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>