Re: subroutine within regex quantifier?

There's the experimental (?{...}) construct, but I can't think of a way to use that. Why not use length and a slightly different regex?

while (length($target_letters) != WORD_LENGTH &&
    $target_letters =~ /[^A-Za-z]/) {
    # prompt
}
[download]

Seems clearer to me, as well as *possible*.