[pro] Is cl-yacc going to cut it?

[Daniel Herring]

On Mon, 14 Feb 2011, William Halliburton wrote:
> I know I'm late to the parade but if you need to write grammars that can be easily augmented by other people without them needing to know much, if any, lisp I can recommend the ebnf parser written by Daniel Herring.  Its onion of
> macros expands into pretty understandable code also.
> 
> http://git.androdna.com/?p=lisp/ebnf-parser

Thank you for the kind words.  That was one of my first real CL projects. 
A great attraction of CL was that I would no longer need to write parser 
code for DSLs...

I always meant to revisit that library, clean it up, and add some more 
features (e.g. support for infinite streams and source locations) but got 
distracted in the land of continuations and never made it back.


Here's a reply to an earlier post.  It was stuck in my drafts folder.

Re the OP: Yes, it sounded like you were abusing the YACC paradigm.


On Sat, 5 Feb 2011, Scott L. Burson wrote:

> Boolean grammars solve both these problems.  Let's look at how they 
work.

...

A few years ago when I was parsing a lot (a motivator towards lisp), I
grew to like recursive-descent parsers and EBNF (the ISO 14977 variant).

AFAICT, the tokenization/parsing divide was mostly a performance hack.
The tokenizer uses a minimal syntax and thus can run quickly.  The parser
has more conditions, but EQL is faster than STRING=.  Thus the two put
together ran fast, and the factorization also simplified specification.

Today, recursive-descent parsers are fast enough for most uses.  Add a
form that prevents backtracks, and they can handle infinite streams of
data.  It is easy to convert most formalisms into this form, and nothing
is more flexible than "write whatever function you want here".

If people are looking for inspiration, ANTLR is a good framework to borrow
ideas from.  Parsing is only half the battle.  Then you reach trees,
walkers, output generation, error handling, etc.  Boost::spirit also has
some good features.

Later,
Daniel