debugging and flow control

[alexxx.magni]

Hi all, I need some advice:

in the past, when writing programs I often used, to help me in
debugging, the following style:

my $debuglevel=1;
.....
print("var value is $a\n") if ($debuglevel>0);
.....
print(LOGFILE "array values are @x\n") if ($debuglevel>2);
....

you get the idea.
Now I'm working on a project very computational-intensive, and I'm
worried about the many lines "if ($debuglevel...)" to be evaluated.

I was wandering: if $debuglevel was a constant, not a variable, it is
possible that the program, when launched, evaluates those lines from
the beginning? In this case I should not worry about later evaluation.

Any other suggestion for flow control?

thanks!

Alessandro Magni

 

[Paul Lalli]

my $debuglevel=1;
....
print("var value is $a\n") if ($debuglevel>0);
....
print(LOGFILE "array values are @x\n") if ($debuglevel>2);
...

you get the idea.
Now I'm working on a project very computational-intensive, and I'm
worried about the many lines "if ($debuglevel...)" to be evaluated.

I was wandering: if $debuglevel was a constant, not a variable,
it is possible that the program, when launched, evaluates those
lines from the beginning? In this case I should not worry about
later evaluation.

That would appear to be accurate....

$ perl -MO=Deparse -e'
my $x = 1;
print "Hello " if $x;
print "World\n" if $x;
'
my $x = 1;
print 'Hello ' if $x;
print "World\n" if $x;
-e syntax OK


$ perl -MO=Deparse -e'
use constant x => 1;
print "Hello " if x;
print "World\n" if x;
'
use constant ('x', 1);
print 'Hello ';
print "World\n";
-e syntax OK


However, I'm not even a little bit convinced that the savings you'll
see from this will be noticeable. I'd try a Benchmark if I were you,
to see if it's worth your time to go through and change your code...

Paul Lalli

 

[Anno Siegel]

Hi all, I need some advice:

in the past, when writing programs I often used, to help me in
debugging, the following style:

my $debuglevel=1;
....
print("var value is $a\n") if ($debuglevel>0);
....
print(LOGFILE "array values are @x\n") if ($debuglevel>2);
...

you get the idea.
Now I'm working on a project very computational-intensive, and I'm
worried about the many lines "if ($debuglevel...)" to be evaluated.

Especially if the program is computational-intensive, it is unlikely
that skipping debug statements is going to make a noticeable difference.

I was wandering: if $debuglevel was a constant, not a variable, it is
possible that the program, when launched, evaluates those lines from
the beginning? In this case I should not worry about later evaluation.

If needed, that can be done using the constant pragma. The technique
is described in "perldoc constant", so I don't have to repeat it here.

Anno

 

[alexxx.magni]

Especially if the program is computational-intensive, it is unlikely
that skipping debug statements is going to make a noticeable difference.


If needed, that can be done using the constant pragma. The technique
is described in "perldoc constant", so I don't have to repeat it here.

Anno

Maybe I could be clearer: yes, I was talking about "use constant...".
Do you know if this:

use constant DEBUGON=>1;
if (DEBUGON>0) {...}

is evaluated, the if eliminated and the block {...} accepted, prior to
the global run?


thanks!

Alessandro

 

[Anno Siegel]

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Maybe I could be clearer: yes, I was talking about "use constant...".
Do you know if this:

use constant DEBUGON=>1;
if (DEBUGON>0) {...}

is evaluated, the if eliminated and the block {...} accepted, prior to
the global run?

There are at least two ways you could find out yourself. Take a look at
"perldoc constant" as recommended in my last reply. Or use the O:eparse
function to see directly what the compiler makes of your statement.

Anno

 

[Paul Lalli]

There are at least two ways you could find out yourself. Take a
look at "perldoc constant" as recommended in my last reply. Or
use the O:eparse function to see directly what the compiler
makes of your statement.

Which is, of course, exactly what I did for the OP in the first reply
to this thread three days ago. . .

Paul Lalli