Tracing your program

You can use the REXX interactive trace facilities to understand what is happening in your program.

For details about the TRACE instruction, see TRACE.

To find out where your program is going, use TRACE Labels. The example shows a program and the trace it gives on the screen.

Figure 1. ROTATE

/* ROTATE */

/* Example: two iterations of wheel, six iterations */
/* of cog. On the first three iterations, "x < 2"   */
/* is true. On the next three, it is false.         */
trace L
do x = 1 to 2
wheel:
   do 3
cog:
      if x < 2 then do
true:
      end
      else do
false:
      end
   end
end
done:

This gives the following trace:

rotate
     6 *-* wheel:
     8 *-* cog:
     10 *-* true:
     8 *-* cog:
     10 *-* true:
     8 *-* cog:
     10 *-* true:
     6 *-* wheel:
     8 *-* cog:
     13 *-* false:
     8 *-* cog:
     13 *-* false:
     8 *-* cog:
     13 *-* false:
     17 *-* done:

To see how the language processor is computing expressions, use TRACE Intermediates.
To find out whether you are passing the right data to a command or subroutine, use TRACE Results.
To make sure that you get to see nonzero return codes from commands, use TRACE Errors.