Suffers from the same problem the OP describes. If you would use that grep a second time (because it's in a sub, or in a loop), the $z doesn't get reset -- that's what state is doing.

Better (but untested):

my @y = do {my $z = 0; grep {$z ||= $_ == 3} @x};
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Note that doesn't evaluate the condition ($_ == 3) after finding a match.