Well, I'd do: 
sub is_const { !eval { ($_[0]) = $_[0]; 1; } }

for (...) {
  if (is_const($_)) { ... }
  else { ... }
}

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japhy -- Perl and Regex Hacker

In reply to Re: Detecting constant arguments passed to subroutines by japhy
in thread Detecting constant arguments passed to subroutines by dcd

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