Forcing a BLOCK rather than an instruction after an if is because of a simple reason: the "dangling else". It is not apparent in which way if $condition if $more_condition do_something() else do_other() is to be disambiguated; many tradiditional languages arbitrarily choose to bind the else branch to the closest if, but that's not readily apparent from looking at the code - and if you want to bind the else of the first if, you still have to use a BLOCK around the second.

So Perl forces you to use BLOCKs for clarity, but lets you append an if clause as a statement modifier for when you want brevity: do_something if $condition;.

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