[TRE-general] Repeat histories

[Chris Kuklewicz]

Rici Lake wrote:
> 
> If I get really enthusiastic, I might even code that to see if
> it works :)
> 

Thanks from bringing more C.S. knowledge into this.  As a physicist I bring very
little formal C.S. to the table.

And Rici Lake wrote:
>> a bunch of handwaving
> 
> I forgot to mention, although I suppose it's obvious:

:) "Proof by intimidation"
http://www.everything2.com/index.pl?node_id=961354&lastnode_id=0

> 
> If we establish that a given sub-expression (R)* is
> right-matchable, then we do not need ordinals at all;
> we can get the Posix semantics by using the shortest-
> non-empty-match rule for the last capture.

I am unlikely to believe that: (right-matchable property) implies (the shortest
final iteration implies Posix semantics).

Let me see if I can construct a counter example...

R = "a|ab|b"
R* = "(a|ab|b)*"

L(R*) is "" or any sequence of a's and b's

Lm(R*) is also "" or any sequence of a's and b's.

Since Lm(R*) == L(R*) I claim R has the right-matchable property.

Match R* against text "ab" two different ways:

The longest first iteration, used by Lm(R*), is "ab" which is the correct Posix
answer.

The shortest non-empty final iteration is "b" which not the correct Posix answer.

Further comment: The longest-final-match and shortest-final-match often imply
perverse things about the previous sequence of matches.

-- 
Chris