Re: --no-parser options

[Hans Aberg]

On 6 Aug 2007, at 12:19, tim wrote:

> > > --no-parser would be quite useful to me. I want to use the parse
> > > tables
> > > in a lisp program. The less C code I have to filter out the better.
> >
> > It sounds you want to generate a LISP parser. Have you thought of
> > writing a skeleton file for generating LISP output, which might (some
> > day) be included in the Bison distribution?

> If that's feasible, it's probably what I will do. The alternatives  
> would
> be to write my own parser generator, or trawl through the bison  
> output.
> I've printed out the M4 manual so I can understand the skeletons.

Bison has been changed in order to facilitate that, including adding  
M4, but it is hard to foresee the practical difficulties if you do  
with say Lisp or Scheme. Learning whole M4 is very ambitious: one can  
start tweaking the skeleton file, by comparing with the output. One  
hurdle is figuring out how to translate the rather imperative style  
of the parser (a so called push-down automaton to which Bison merely  
computes the states) into a functional language. The parser function  
checks if a new token is needed, and if there results in a reduction,  
the action is performed in a large "switch" statement, and then it  
loops back again, until the virtual end symbol arrives (the parser  
stack has completely been reduced). The parse stack has different  
components: state, semantic value, location, perhaps more, which can  
be implemented as a single stack, or several. At least in the past,  
the Bison skeleton file did the latter.

  Hans Aberg