In the second case, print is being interpreted as a function, i.e. print(WEEKDAYS)[1];, where the [1] doesn't work. Normally this gets a warning, but you've run into a case where it doesn't:

$ perl -we 'print (3+4),5;'
print (...) interpreted as function at -e line 1.
Useless use of a constant (5) in void context at -e line 1.
7
$ perl -we 'print (WEEKDAYS)[1];'
print (...) interpreted as function at -e line 1.
syntax error at -e line 1, near ")["
Execution of -e aborted due to compilation errors.
$ perl -we 'print  (WEEKDAYS)[1];'
syntax error at -e line 1, near ")["
Execution of -e aborted due to compilation errors.

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Two workarounds in addition to your "case #1":

$ perl -we 'print +(3+4),5;'  # disambiguate
75
$ perl -we 'print((3+4),5);'  # explicit parens
75

[download]

Tip: B::Deparse comes in handy for debugging here:

$ perl -MO=Deparse,-p -e 'print (3+4),5;'
(print(7), '???');

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In reply to Re: use constant moudle by Anonymous Monk
in thread use constant module by Hosen1989

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