On Apr 18, 2010, at 2:02 PM, Terence Parr wrote:
> More importantly, I'm approximating recursive lexer rules with a DFA and
> then will invoke the recursive method at runtime after I've distinguished the
> input from other rules. What I mean is that, I really kind of need to build
> a DFA :)
Hmm...if we allow a stack of lexical states ("modes") then we don't need
recursive lexer rules, which I rarely use anyway. Here's how we could do
nested comments:
ID : ... ;
INT : ... ; // usual stuff
CMT_START : '/*' {pushMode(COMMENTS);} ;
mode COMMENTS:
NESTED_CMT_START : '/*' {pushMode(COMMENTS);} ;
CMT_STOP : '*/' {popMode();} ;
ANY : . ;
That's not as "cool" as this though:
ID : ... ;
INT : ... ; // usual stuff
CMT : '/*' (CMT | .)* '*/' ;
That said, my current thoughts on impl would match CMT approximately and then
rewind to call the generated CMT method and exec it as if it were a parser
rule. Less efficient. Worse, if approx predicted two recursive methods, I'd
have to try both with backtracking...hmm...so maybe we really should avoid
recursive lexer rules in favor of states, which handles nongreedy situations
and recursion.
Ter
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