[antlr-interest] Why don't parsers support character ranges?

Hannes Schmidt antlr5 at hannesschmidt.net
Thu Apr 24 16:38:26 PDT 2008

Eamon Nerbonne wrote:
> The suggestion has been made that parsers and lexers need to be 
> separated, or that combining them would be a subject for a thesis.  
> This isn't new work, however: there exist such things, like say...
> DParser - Scannerless GLR parser
> With juicy bits like:
> "[...]The grammar can be ambiguous, right or left recursive, have any 
> number of null productions, and because there is no seperate 
> tokenizer, can include whitespace in terminals and have terminals 
> which are prefixes of other terminals.[...]"
> http://dparser.sourceforge.net/
> GLR techniques can actually parse ambiguous constructs, which is a 
> boon when it comes to things like C's dangling else.  I'm not an 
> expert, but IIRC these parsers are all descendants of Tomito's GLR 
> parser, which was (almost) capable of parsing ambiguous constructs but 
> contained a few errors (with nullable items and hidden left recursion) 
> and wasn't very efficient on ambiguous grammars.  Newer algorithms 
> have fixed both issues.
> I believe scannerless parsing is possible with the a little more well 
> known Elkhound, and a bit of web-searching also revealed meta-environment
> http://www.cwi.nl/htbin/sen1/twiki/bin/view/Meta-Environment, and 
> there's lots more out there.
This is great help, Eamon. I'll digg into these right away. I did some 
search, too, but it didn't lead anywhere. Thank you!

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