Some of what you say I can agree with. But "they only exist within a lexical scope"---and why's that? It's because lexical variables cannot access the symbol table. That's why I mentioned that there's a control "sandboxed" way from the debugger. Package variables can be accessed via the symbol table.

As for my $a getting optimized away, I disagree with that because I just don't see how it can be optimized away when it's uninitialized in the subroutine. Here's a little test that I ran:

#!/usr/bin/perl

use strict;
use warnings;

print mt2(55), "\n";

my $a = 23;

sub mt2 { 
    my $b = $_[0] * 2;
    return $a + $b;
}
[download]

Here's the corrected script:

#!/usr/bin/perl

use strict;
use warnings;

print mt2(55), "\n";

sub mt2 { 
    my $a = 23;
    my $b = $_[0] * 2;
    return $a + $b;
}
[download]

This one works in the debugger. Thanks for the input.

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