To trace operations within an expression, use the TRACE I (TRACE Intermediates) form of the TRACE instruction. All expressions that follow the instruction are then broken down by operation and analyzed as:

>V>   - Variable value - The data traced is the contents
        of a variable.
>L>   - Literal value - The data traced is a literal
        (string, uninitialized variable, or constant).
>O>   - Operation result - The data traced is the result
        of an operation on two terms.

The following example uses the TRACE I instruction.

EDIT ---- USERID.REXX.EXEC(SAMPLE) ---------------------- COLUMNS 009 080
COMMAND ===>                                             SCROLL ===> HALF
******* ************************** TOP OF DATA ****************************
000001 /************************* REXX *****************************/
000002 /*  This exec uses the TRACE instruction to show how an     */
000003 /*  expression is evaluated, operation by operation.        */
000004 /*********************************************************  */
000005  x = 9
000006  y = 2
000007  TRACE I
000008
000009  IF x + 1 > 5 * y THEN
000010     SAY 'x is big enough.'
000011  ELSE NOP                  /* No operation on the ELSE path */
******* ********************** BOTTOM OF DATA *****************************

When you run the example, you see on your screen:

  9 *-* IF x + 1 > 5 * y
    >V>   "9"
    >L>   "1"
    >O>   "10"
    >L>   "5"
    >V>   "2"
    >O>   "10"
    >O>   "0"

First you see the line number (9 *-*) followed by the expression. Then the expression is broken down by operation as follows:

>V>   "9"    (value of variable x)
>L>   "1"    (value of literal 1)
>O>   "10"   (result of operation x + 1)
>L>   "5"    (value of literal 5)
>V>   "2"    (value of variable y)
>O>   "10"   (result of operation 5 * y)
>O>   "0"    (result of final operation 10 > 10 is false)