$ perl -wle'
my %x = (42,23);
warn Dumper \%x'
Backslash found where operator expected at -e line 3, near "Dumper \"
    (Do you need to predeclare Dumper?)
Missing comma after first argument to warn function at -e line 3, at EOF
Execution of -e aborted due to compilation errors.

$ perl -wle'
use Data::Dumper;
my %x = (42,23);
warn Dumper \%x'
$VAR1 = {
          '42' => 23
        };