Padding a string with spaces

[StephenG1CMZ]

I decided to have a go at this, based on the original syntax.
My changes include:
An input guard against negative/fractional parameters.
The input string is not modified.
In the centre case, a recursive call is used which I think makes the logic clearer, and avoids repeatedly adding spaces one by one. My implementation is probably less efficient, but provides a comparison for the previous logic.

Code:


 
 EXPORT ZPAD(ST,LNG,DD)
 //ST PADDED NOT TRUNC
 //LNG IS OUT MINLEN
 //DD 1 R −1 L 0 C
 BEGIN
  LOCAL LL:=ABS(IP(LNG));//INGUARD
  LOCAL SPC:=LL-DIM(ST);
  LOCAL SPTMP:="";

  CASE
  IF DD>0 THEN //PAD R
   RETURN REPLACE(ST,LL+1,"");//SYN:JOE HORN
  END;
  IF DD<0 THEN //PAD L 
   RETURN REPLACE("",SPC+1,ST);
  END; 
  DEFAULT  //PAD C
   SPTMP:=ZPAD("",SPC/2,1);//spaces
   SPTMP:=SPTMP+ST+SPTMP;
   RETURN 
    IFTE(DIM(SPTMP)<LL,SPTMP+" ",SPTMP);//extra space if odd
  END;//CASE
 END;

 //LAYERED
 EXPORT ZPADL(ST,LL)
 BEGIN
  RETURN ZPAD(ST,LL,−1);
 END;
 
 EXPORT ZPADR(ST,LL)
 BEGIN
  RETURN ZPAD(ST,LL,1);
 END;

 EXPORT ZPADC(ST,LL)
 BEGIN
  RETURN ZPAD(ST,LL,0);
 END;


 EXPORT ZS()
 BEGIN 
  LOCAL ST:="";
  LOCAL STIN:="ABC";
  //PRINT();


  ST:=ZPAD(STIN,9,1);
  //PRINT(SIZE(STIN));//unchanged
  //PRINT(SIZE(ST));
  //PRINT("v"+ST+"V");//v just shows text limits
  //WAIT;
 END;