Re: while ()

Very interesting. A special-case idiom that never caught on (people still use while(1)). Note that it is a very special case of there being no expression. while(()) and while(do{}) never loop. And you can't mimic the behavior in predicate while, because the parentheses are optional: ... while; is a syntax error, and ... while (); is the same as ... while (());

Update: I didn't mean it's a very special case out of the set of cases where there is no expression; I meant that there being no expression is a very special case (that you can't mimic with any expression). The documentation specifies that while takes an expression.

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Re^2: while () by Neutron Jack (Pilgrim) on Jun 08, 2005 at 02:13 UTC
I don't believe that `while(())` is an example of no expression. Rather, `while(())` evaluates the condition `()`, a list of no elements. A list evaluated in scalar conext yields the last element, according to man perldata: If you evaluate an array in scalar context, it returns the length of the array. (Note that this is not true of lists, which return the last value, like the C comma operator, nor of built-in functions, which return whatever they feel like returning.) What's the "last value" of an empty list? Experiments indicate that it's `undef`, a false value, so the while-loop doesn't loop.	[reply] [d/l] [select]

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Re^2: while ()
by Neutron Jack (Pilgrim) on Jun 08, 2005 at 02:13 UTC

while(())

()

man perldata

If you evaluate an array in scalar context, it returns the length of the array. (Note that this is not true of lists, which return the last value, like the C comma operator, nor of built-in functions, which return whatever they feel like returning.)

undef

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