[stack] Parsing in Factor

I wrote a Packrat parser in Factor, with an embedded DSL for
generating grammars;

http://www.bluishcoder.co.nz/2007/11/embedded-grammars-in-factor.html

With this you can write Factor code like:

<EBNF
expr = number {('+'|'-') number}
EBNF>

This creates a word 'expr' that can parse text like "123+456-789". The
blog post shows the full grammar for the PL/0 programming language and
it looks very much like the definition of the language from Wikipedia.
The EBNF grammar parser is written using a series of packrat parser
combinator words I wrote.  The grammar above using the low level words
would look like:

: expr ( -- parser )
  [
    number ,
    [
      [
        "+" token , "-" token ,
      ] { } make choice ,
      number ,
    ] { } make seq repeat0 ,
  ] { } make seq ;

It's still a work in progress and I'm currently extending it to allow
left recursive rules, but hopefully it'll make designing domain
specific languages easier.

Chris.
-- 
http://www.bluishcoder.co.nz