Re: re2c-1.0 released!

On 2017-08-27, Ulya Trofimovich <skvadrik@gmail.com> wrote:
> Hello everybody,
>
>
> I'm glad to announce the new major release of re2c lexer generator, 1.0.
> re2c specializes in generating fast and flexible lexers; it was written
> by Peter Bumbulis around 1994 [0] and since then maintained by many
> people. See release notes for the full story [1].
>
> The main breakthrough of this release is the addition of fast submatch
> extraction: re2c now supports capturing groups with POSIX longest-match
> semantics, as well as standalone capturing "tags" with leftmost greedy
> semantics. The implementation is based on the efficient novel algorithm [2].
>
> The challenge of adding submatch extraction to a lexer generator is not
> immediately obvious: this feature is provided by many regular expression


Neither is obvious the advantage/utility of this.


> libraries and command-line tools like grep and sed.


They exist in support of very flimsy, ad hoc approaches for
dealing with some text processing problems.


Briefly, why would you do some hacky regex thing in lex with \1, \2,
\3, when in the level immediately above yylex() you have proper phrase
recognition, with $1, $2, $3.


(What is that, if not a better grade of backreferencing.)


> It may seem that
> only a lack of effort prevents developers of lexer generators like Flex
> from implementing it (as well as fixing the ever-broken trailing
> contexts [3]).


Lack of justification due to, I suspect, lack of demand from
sophisticated users of the tools, who use them for their intended
purpose.

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