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NetRexx Overview, version 2.02
Copyright (c) IBM Corporation, 2001. All rights reserved. © | 22 May 2001 |
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Tracing
NetRexx tracing is defined as part of the language. The flow of execution of programs may be traced, and this trace can be viewed as it occurs (or captured in a file). The trace can show each clause as it is executed, and optionally show the results of expressions, etc. For example, the trace results in the program ‘trace1.nrx’:trace results number=1/7 parse number before '.' after say after'.'beforewould result in:
--- trace1.nrx
2 *=* number=1/7
>v> number "0.142857143"
3 *=* parse number before '.' after
>v> before "0"
>v> after "142857143"
4 *=* say after'.'before
>>> "142857143.0"
142857143.0
where the line marked with ‘---’ indicates the context
of the trace, lines marked with ‘*=*’ are the
instructions in the program, lines with ‘>v>’
show results assigned to local variables, and lines with
‘>>>’ show results of un-named expressions.
Further, trace methods lets you trace the use of all methods in a class, along with the values of the arguments passed to each method. Here's the result of adding trace methods to the Oblong class shown earlier and then running tryOblong:
--- Oblong.nrx
8 *=* method Oblong(newwidth, newheight)
>a> newwidth "5"
>a> newheight "3"
26 *=* method print
Oblong 5 x 3
20 *=* method relsize(relwidth, relheight)-
21 *-* returns Oblong
>a> relwidth "1"
>a> relheight "1"
26 *=* method print
Oblong 6 x 4
10 *=* method Oblong(newwidth, newheight)
>a> newwidth "1"
>a> newheight "2"
26 *=* method print
Oblong 1 x 2
where
lines with ‘>a>’ show the names and values of the
arguments.
It's often useful to be able to find out when (and where) a variable's value is changed. The trace var instruction does just that; it adds names to or removes names from a list of monitored variables. If the name of a variable in the current class or method is in the list, then trace results is turned on for any assignment, loop, or parse instruction that assigns a new value to the named variable.
Variable names to be added to the list are specified by listing them after the var keyword. Any name may be optionally prefixed by a - sign., which indicates that the variable is to be removed from the list.
For example, the program ‘trace2.nrx’:
trace var a b -- now variables a and b will be traced a=3 b=4 c=5 trace var -b c -- now variables a and c will be traced a=a+1 b=b+1 c=c+1 say a b cwould result in:
--- trace2.nrx
3 *=* a=3
>v> a "3"
4 *=* b=4
>v> b "4"
8 *=* a=a+1
>v> a "4"
10 *=* c=c+1
>v> c "6"
4 5 6
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From
The NetRexx Language by
Mike Cowlishaw,