C:\tmp\e>perl
($a,$b) = (7,3);
my $x=5;
my $inside = do {
    local ($a,$b) = ($b,$a) if $b < $a;
    $a <= $x < $b ;
};
print "$x in [$a, $b]? $inside";
__END__
5 in [7, 3]? 1
C:\tmp\e>