So I'm writing some code to perfect-shuffle two lists, and I want it to complain when it doesn't get lists of equal length. Which style is preferred?

# .. or warn is homomorphic to the .. or die idiom, and is
#  phrased like an assert.
@foo == @bar
  or warn "perfect_shuffle: lists must have equal length\n";

# explicit if makes adding cleanup easier, and is phrased
#  like an error check.
if(@foo != @bar) {
  warn "perfect_shuffle: lists must have equal length\n":
}
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Edit: s/scalar \@/\@/g;; thanks adrianh!