On 2011-09-28 22:59, Jonathan M Davis wrote:
On Wednesday, September 28, 2011 13:43 Nick Sabalausky wrote:
"Jonathan M Davis"<[email protected]> wrote in message
news:[email protected]...
I would point out that there is an intention to eventually get a D lexer
and
parser into Phobos so that tools can take advantage of them. Those could
eventually lead to a frontend in D but would provide benefits far beyond
simply
having the compiler in D.
Is the interest more in a D-specific lexer/parser or a generalized one? Or
is it more of a split vote? I seem to remember interest both ways, but I
don't know whether there's any consensus among the DMD/Phobos crew.
A generalized lexer is nothing more than a regex engine that has more than
one distinct accept state (which then gets run over and over until EOF).
And the FSM is made simply by doing a combined regex "(regexForToken1 |
regexForToken2 | regexForToken3 | ... )", and then each of those parts
just get their own accept state. Which makes me wonder...
There was a GSoC project to overhaul Phobos's regex engine, wasn't there?
Is that done? Is it designed in a way that the stuff above wouldn't be
real hard to add?
And what about algoritm? Is it a Thompson NFA, ie, it traverses the NFA as
if it were a DFA, effectively "creating" the DFA on-the-fly)? Or does it
just traverse the NFA as an NFA? Or does it create an actual DFA and
traverse that? An actual DFA would probably be best for a lexer. If a DFA,
is it an optimized DFA? In my (limited) tests, it didn't seem like
DFA-optimization would yield a notable benefit on typical
programming-langauge tokens. It seems to be more suited to pathological
cases.
There is some desire to have a lexer and parser in Phobos which basically have
the same implementation as dmd (only in D instead of C++). That way, they're
very close to the actual compiler, and it's easy to port fixes and
improvements between the two.
However, we definitely also want a more general lexer/parser generator which
takes advantage of D's metaprogramming capabalities. Andrei was pushing more
for that and doesn't really like the idea of the other, since it would reduce
the desire to produce the more general solution. So, this _is_ some dissension
on the matter. But there's definitely room for both. It's just a question of
time and manpower.
- Jonathan M Davis
I would rather have a D specific lexer/parser than a general
lexer/parser generator,
--
/Jacob Carlborg
