Re: Question about Lexx & Yacc

[Axel Kittenberger]

English is not context-free, right?

> At 15:20 -0700 1-01-11, Nattapong wrote:
> >please take a look at my "ch1-05.y".
> ...
> >%token NOUN PRON VERB ADV ADJ PREP CONJ
> >
> >%%
> >
> >sentence: subject VERB object { printf ("Sentence is valid.\n"); }
> >   ;
> >
> >subject:     NOUN
> >       |    PRON
> >       ;
> >object:        NOUN
> >       ;
> >%%
> 
> If you intent is to write a parser for the English language, there is
> already a large project for that going on, see for example
>   http://lands.let.kun.nl/TSpublic/tosca/
> 
> One problem is that the same English word (or group of words) may have a
> set of different token values. Bison cannot handle this; an interesting
> question is how to modify Bison so that it can.
> 
> The same problem happens when implementing the grammar used in common
> mathematics -- I once write a simple recursive decent parser that could
> handle such a situation.
> 
> With the current Bison, you could handle the situation by letting the
> Bison
> grammar sending back context information to the (F)lexer.
> 
>   Hans Aberg
> 
> 
> 
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