Editing COMEFROM (section)

=== OS/360 Fortran G ===
The OS/360 Fortran G compiler has a debug packet feature. Its "AT" statement is similar to COMEFROM in that it hands the control flow over to the debug block. [[Breakpoint]]s in general are similar.<ref>IBM System/360 and System/370 Fortran IV Language, GC28-6515-10, May 1974</ref>

* Example 1: the values of SOLON, GFAR, and EWELL are examined as they were at the completion of statement 10.  The AT statement indicates statement 11.
<syntaxhighlight lang="fortranfixed">
      INTEGER SOLON, GFAR, EWELL
         .
         .
         .
10    SOLON = GFAR * SQRT(FLOAT(EWELL))
11    IF (SOLON) 40, 50, 60
         .
         .
         .
      DEBUG UNIT(3)
      AT 11
      DISPLAY GFAR, SOLON, EWELL
      END
</syntaxhighlight>
* Example 2: all the values of STOCK are displayed when statement 35 is encountered.
<syntaxhighlight lang="fortranfixed">
      DIMENSION STOCK(1000),OUT(1000)
         .
         .
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      DO 30 I=1, 1000
25    STOCK(I)=STOCK(I) - OUT(I)
30    CONTINUE
35    A = B + C
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         .
         .
      DEBUG UNIT(3)
      AT 35
      DISPLAY STOCK
      END
</syntaxhighlight>
* Example 3: tracing begins at statement 10, at statement 20, tracing stops while the loop is executed, and resumes after the loop.  Tracing stops just before statement 30 is executed.
<syntaxhighlight lang="fortranfixed">
10    A = 1.5
12    L = 1
15    B = A + 1.5
20    DO 22 I = 1,5
         .
         .
         .
22    CONTINUE
25    C = B + 3.16
30    D = C/2
      STOP
         .
         .
         .
      DEBUG UNIT(3), TRACE
C     DEBUG PACKET NUMBER 1
      AT 10
      TRACE ON
C     DEBUG PACKET NUMBER 2
      AT 20
      TRACE OFF
      DO 35 I = 1,3
         .
         .
         .
35    CONTINUE
      TRACE ON
C     DEBUG PACKET NUMBER 3
      AT 30
      TRACE OFF
      END
</syntaxhighlight>