Thanks to all who answered my question.

I learned that there are many way to do one task.
I adopted 
   .==================================================
    (print error_msg; exit 1) if error_flag
   .==================================================
because it is the easiest way to understand, I think.

regards,
kwatch



Mark Slagell <ms / iastate.edu> wrote in message news:<3D36F1E8.1040605 / iastate.edu>...
> GOTO Kentaro wrote:
> 
> >[snip]
> >
> >
> >Array syntax works as sequential control, e.g., 
> >
> >  [ print(error_message), exit(1) ] if error_flag
> >
> >  error_flag and [ print(error_message), exit(1) ]
> >
> >if you could accept these unconventional application :)
> >
> 
> Or,
> 
>   (print error_message; exit 1)  if error_flag