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Re: --no-parser options

From: Hans Aberg
Subject: Re: --no-parser options
Date: Mon, 6 Aug 2007 21:28:05 +0200

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

--no-parser would be quite useful to me. I want to use the parse
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

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