Atwood, Robert C said:
... (snobal text removed) ...
>
> Any thoughts on using a tool like lex/yacc / flex/bison for parser
> generation?
For the parser that I am working on, I am using Python. I
have the complete parser working now, using simpleparse, which
uses an EBNF description as its input. I am currently working
on the API and filling in the data structures from the
callbacks. The basic structure of my parser is this:
A) Run a preprocessor that does the following:
1) Determine if I am looking at pre-2.0 ABC or not.
2) Remove line continuations (doing it correctly depending
on the ABC version)
3) Remove all % style comments (not %% directives) and store
them for later use (if needed).
4) In pre-2.0 ABC files, if ! is used as a decoration marker
(!ff!), then change it to 2.0 syntax: +ff+.
5) If an H: field is found in the header, then any lines that
follow it that do not start with '%%' or have ':' as the
second character will be changed to have 'H: ' before them.
(I believe that this is a problem in the 2.0 specification,
which says that the H: is a multiline header - it is
a royal pain to do this nicely in the BNF, do I handle
it here).
6) The %% syntax is irrelevant with the new I: format. As
such, the %% syntax is removed and replaced with I: format.
B) Use an EBNF description to completely parse the file. I am
using an EBNF that I wrote that is based on the ABC 2.0 ABNF
written by Henrik Norbeck. I added a couple of things to the
EBNF to allow parsing older ABC files and corrected a number
of mistakes and places where the grammar was ambiguous.
C) The parser calls callbacks in python which I use to populate
the data structures. I am still working on the data structures
that I use.
So far, I have been able to parse all of the ABC files in my
small test suite (about 10 ABC files, including a couple of
very large files).
You can find the code as it stands right now at:
http://www.purecode.com/~tsatter/python/
tom
--
tom satter - or just plain old tom
(303) 543-7623 (home)
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