C[omp]ute

From: "andrew cooke" <andrew@...>

Date: Sat, 12 May 2007 20:16:55 -0400 (CLT)

That's an overstatement, but anyway, talking to myself here trying to get
thsi clear.

- RFC223 defines the ABNF grammar.

- By hand, we fine-tune the ABNF parser, which is hand-written based on
the RFC (ie choose which nodes are labelled, ignore or preserved).

- This parser is "abnf-description-for-foo -> abnf-format-ast-for-foo"

- Next we write a translator that is specific to abnf format asts.  It
takes ASTs in ABNF format and generates a parser combinator for the
described format.  This is easy because theer's a very close mapping
between ABNF and parser combinators.  So it's mainly a tree rewrite (using
catana).

- This tree rewriter is a "abnf-format-ast-for-foo -> parser-for-foo".

- We make the rewriter configurable so that you can select which nodes are
labelled, ignored or preserved.

- To complete the circle we run the ABNF parser on the ABNF description. 
This gives us an ABNF format tree for ABNF itself.

- We run the rewriter on this, configuring it so that the result matches
out initial hand-written parser (same nodes ignored etc).  This gives us a
new parser for ABNF which can replace the hand-written one.

Andrew