Okay, we've traded a simple, extensible, easily used and self-documenting construct for YAKW and less self documenting code.

I often use

...
my( $p, $i ) = 0;
$p += $i while $i = 1+index $haystack, $needle, $i;
...
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Sometimes, when debugging I need to see what is going on, so I wrap the code and add some debug:

...
my( $p, $i ) = 0;
do{ 
    $p += $i;
    print "$p : $i, other stuff";
} while $i = 1+index $haystack, $needle, $i;
...
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Once I'm done debugging, I can just comment out the print lines and I am back to where I was.

In p6, I will have to completely change the coding of the single line with modifier version of the loop to an alien and less clear construct when I need to debug, and convert it back once I have the logic correct. Or leave as that strangly Fortran IV-ish form:

my( $p, $i ) = 0;
loop {
    $p += $i;
    last if $i = 1+index $haystack, $needle, $p;
}
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I know "LW is always right" and "LW is always right even when he is wrong", but on this I think he has never been more right.