Re: Grammars are not Regexps

Looks interesting!

I await the results with interest.

In the meantime, if you can share the grammar, I might have time to try out the parses in JayParser in the morning (these look short enough that they might actually finish parsing!)

Thanks,
Tom

_________________
Tomos Hillman
eXpertML Ltd
+44 7793 242058
On 3 Feb 2022, 21:06 +0000, Steven Pemberton <steven.pemberton@cwi.nl>, wrote:
> I was working on some grammars this week, and tripped up a couple of times,
> getting ambiguous grammars, I think because I was thinking in regexp terms,
> and grammars are not regexps.
> The place where this was obvious was with repetition. Regexps are greedy,
> grammars aren't. So "x"* with a regexp will match a maximal number of x's,
> but not necessarily with a grammar.
>
> I reduced it to a small example in order to work on it more, and I
> thought maybe some of you would like to try it out too, before I give an
> example answer. I found it quite instructional.
>
> It's Pascal-style comments (XML comments would work similarly), comments
> surrounded by (* and *).
>
> Here is a test set:
>
> (**)
> (***)
> (****)
> (*****)
> (*abc*)
> (**abc*)
> (*abc**)
> (*abc*abc*)
> (**abc*abc*)
> (*abc**abc*)
> (*abc*abc**)
> (*abc* )(*abc*)
> (*abc*)(*abc*)
>
> (The last line contains two comments; the line before has a space before
> the first closing bracket).
>
> It was trickier than I expected at first, because as I said, although I was
> parsing the comments OK, the results were ambiguous.
>
> Steven
>