Thanks, now I understand the difference: in the first case '()' wanted in scalar context which was forced by 'if' (so it becomes an undefined value).

Added:
An 'if' forces scalar context as 'and' do, so it may be that these two are internally implemented the same.

In reply to Re^6: printing unitialized value of the 'do BLOCK' by rsFalse
in thread printing unitialized value of the 'do BLOCK' by rsFalse

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