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Postings from April 2014
On 19 September 2012 02:15, David Knipe <pure.mathmo@googlemail.com> wrote:
> I see two problems with this:
> (1) For the lazy match, it still gives the same result as the
> documentation file suggests.
For lazy match isn't it just:
S{0,1}= S??
S{1,2}= SS??
S{1,3}= SS??S??
S{2,4}= SSS??S??
And it seems to me that Zeframs and my definitions are the same.
> (2) It could be taken to mean that the interpreter tries out all possible
> combinations, which could drastically slow things down. For instance, if S
> is just a single character, it could (in some hypothetical worst-case
> scenario) have to try 2**n combinations just to match S{0,n}. If n=3, the
> combinations would be: (S)(S)(S), (S)(S)(), (S)()(S), (S)()(), ()(S)(S),
> etc. Presumably, it is in fact intelligent enough not to try (S)(S)(),
> (S)()(S) and ()(S)(S) separately, in which case the number of things to try
> is only linear.
This is a comment about how the regexp engine implements the match,
not what it legally can match.
It seems to me that in a formal definition we only need the latter.
Yves
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