This really works???

Anyway I think I have a better idea, you can use this hack to evaluate code within a pseudo-var

  DB<100> w @{[$z++]}
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this watch-point will break at each line, cause the value changes.

Now if you include a condition to change only, if your filter matches, you got what you need! :)

edit

  DB<101> w @{[$z++]}

  DB<102> r
0
Watchpoint 0:    @{[$z++]} changed:
    old value:    '0'
    new value:    '1'
main::(tst.pl:12):    say $x++;
  DB<102> r
1
Watchpoint 0:    @{[$z++]} changed:
    old value:    '1'
    new value:    '2'
main::(tst.pl:13):    print $x++;
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