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@a = qw( food foot );
foreach (@a) { s/foo/bar/g }
# @a is now qw( bard bart )

sub visit_breadth_first {
   my ($node, $visitor) = @_;
...
      &$visitor($current);
   }
}

@a = map  { ... transformation ... } @a;
@a = grep { ... filter         ... } @a;
@a = sort { ... equiv test     ... } @a;