in reply to use constant with parentheses

You are right and if you like your constants to behave more like real variables, check-out the Readonly module. Conway suggests to use Readonly rather than use constant as one of his "Best Practices".

CountZero

A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James

In Section Seekers of Perl Wisdom