Re: How are regexen implemented in Emacs?

[Stefan Monnier]

> Perl does the latter. That has saved my bacon from time to time.
> So that seems possible with a backtracker, too.  Don't ask me how,
> though :-)

Indeed, it's not more difficulty to allow to run ELisp/Perl
code in the middle of the backtracking match than a non-backtracking
one, but the difference is in the number of times the ELisp/Perl code
may need to be run, which changes the performance profile (and hence
the potential use-cases) significantly.


        Stefan


PS: Regarding non-backtracking matchers are backreferences, most of the
uses of backreferences I'm familiar with *can* be implemented without
backtracking because the subgroup to which the backref points has only
one possible way to match.  It won't handle cases like
`diff-merge-strings`, but it's still an important subset of cases.