=> is sometimes called a "fat comma". A normal comma is , ... Try it.

use constant {
    NULL => 0,
    EINS => 1,
    ZWEI => 2,
};
my %english_translation = (
    NULL, "Zero",
    EINS, "One",
    ZWEI, "Two",
);
foreach ( keys %english_translation )
{
    print "$_ = $english_translation{$_}\n";
}
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