Checking that a local expression is zero

[vsht]

Dear all,

I know that it's a stupid question, but I really wasn't able to find an elegant way solve it without complicating
everything too much. So is there a simple way to check if the given local expression is zero during the execution?

Consider for example

S a,b; 
L exp1 = a+b;
L exp2 = a*b;
.sort
id a=-b;
.sort
* More code
print;
.end

here exp1 becomes zero after the id statement, while exp2 is not zero. Ideally, I would like to detect exp1 vanishing and finish the program right here (or maybe jump to the end), instead of going through all the subsequent code instructions.

Cheers,
Vlad

[jodavies]

Yes, I think it is undocumented but you can do, e.g.,

S a,b;
L exp1 = a+b;
L exp2 = a*b;
.sort
id a=-b;
.sort
#do e = {`activeexprnames_'}
   #if `ZERO_`e''
      #message `e' is zero
   #endif
#enddo
.end

[vsht]

Many thanks!

[jodavies]

We should an explanation of this (and UNCHANGED_) to the manual.

[StHagel]

Yes, I think it is undocumented but you can do, e.g.,

S a,b;
L exp1 = a+b;
L exp2 = a*b;
.sort
id a=-b;
.sort
#do e = {`activeexprnames_'}
   #if `ZERO_`e''
      #message `e' is zero
   #endif
#enddo
.end

This loops over all local expressions though, right? Is there a way to check just one specific expression?

[jodavies]

Sure, you use ZERO_exprname for whichever exprname you want.