From: Andrew Johnson <ajohnson@...>
Date: 2006-03-22T01:43:50+09:00
Subject: Re: POLS violation? /\s*/ no match at StringScanner end

On Tue, 21 Mar 2006 22:09:18 +0900, Robert Feldt <robert.feldt@gmail.com> wrote:
> On 3/21/06, Carlos <angus@quovadis.com.ar> wrote:
>> Robert Feldt wrote:
[snip]
>> > Is it a bug or a feature?! I can see arguments for both sides but for
>> > me it violates POLS. Opinions?
>>
>> I think, if it matches /\s*/ at end of string, then it should scan it
>> too; and then, #eos? would never be true (you could scan /\s*/ at the
>> end infinitly).
>>
> My point is that my POLS is that eos? should be true *and* you should
> be able to scan any regexp that can match empty string infinitely at
> the end. If not the behavior at the end is different than from within
> which means that users need to handle the situation differently
> depending on when such regexps are used.
 
While I can see your point, I don't see it as a POLS violation:

  irb(main):014:0> lex =  StringScanner.new("")
  => #<StringScanner fin>

The termination condition for a scanner is eos, and I would expect that
a terminated lexical scanner should consistently *not scan*, regardless of
whether a given pattern (eg, /\s*/, /\z/, /$/, //) could match at eos.

I do expect a different behaviour between a lexical scanner in the middle
of its input, and one that reached its termination condition.

However, the StringScanner docs aren't very explicit about this.

> But my POLS might be "wrong".

ditto :-)

andrew

-- 
Andrew L. Johnson   http://www.siaris.net/
      What have you done to the cat? It looks half-dead.
          -- Schroedinger's wife