In a recent post, I saw a question about why

while ()
     {
     <>;
     last unless /\S/;
     print FILE;
     }
[download]

produced a "Use of uninitialized value $_ in pattern match (m//) ..." warning. This is easily fixed by assigning the value returned by the  <> (diamond) operator (aka the readline function) to the appropriate variable:

c:\@Work\Perl>perl -wMstrict -le
"while ()
      {
      $_ = <>;
      last unless /\S/;
      print qq{>$_<};
      }
"
qeert
>qeert
<
ghjk
>ghjk
<
[download]

(This example works the same under ActiveState 5.8.9 and Strawberry 5.14.4.)

What caught my eye was the null loop condition expression in the
    while () { ...;  last unless ...;  ...; }
infinite loop. I would have thought of something along the lines of
    while (1) { ...;  last unless ...;  ...; }

I'm surprised that a null loop condition expression is accepted by the compiler or, being accepted, that it evaluates as true. Because other boolean "nullities" (undef, the empty string, 0) are false, I would have expected a null condition expression, if it compiled at all, to be false. (A B::Deparse of  while () { ... } shows it to compile to  while (1) { ... } in both Perl versions I tried.)

So, my questions:

• Is there any documentation or discussion of this behavior? (Offhand, I can't find any in a quick scan of perlsyn.)
• What is the rationale for this behavior? (Well, it does make a neat shorthand.)

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