Hi All,

Just wanted to send out a note that I've started work again on the new
parser.  I'm getting back to my list and current working on if-then
style statements.  I just now committed a change so that the new
parser can parse a single if-then-endif block.  Next of course will be
looking at parsing elseif's and else statements, as well as making
sure there aren't dangling else's and then doing rate checks that all
the then statements are of the same rate and that the boolean
condition is of the same rate too.

Anyways, I've also been looking at some other grammars to get some
help.  Ruby's parser in YACC based and wow, it's hairy!  I found this
C grammar today and found it particularly useful to help figure out
how to go about doing if-else:

http://www.quut.com/c/ANSI-C-grammar-y-1995.html

All of this new parser work seems a lot easier than last I was working
on it almost a year ago; perhaps some time off made coming back to it
more fun and enjoyable. =)  Anyways, here's a copy of the last list of
todo's I wrote before I stopped last year:

Csound New Parser
	Clean Up FIles (headers, externs)
	Implement Macro's
	Implement Polymorphic Opcodes
	Optimization
		Constant Folding
		Dead Code Elimination
		Inline Constant Irate Variables
	Implement all Expression types
	Implement If-Then-Else statements
	Implement UDO

Now, most of the polymoprhic opcode work is already done but if I
remember correctly some of the polymorphic types aren't implemented
yet.  I'm planning on taking the two biggest tasks first, namely the
if-then-else statements (already started) and then working on UDO
parsing.  The clean up files tasks may already have gotten done by
John some time back but I'm sure to introduce some code that will need
cleaning so will keep on that the list for later.

Probably the optimization stuff could be done much later.  After most
of the above is done, we'll need to start testing and work on Csound
failing correctly (i.e. showing what didn't parse correctly, giving
line numbers and things like that).  The validation pass will probably
be a part of the testing work (this is currently just an empty stub
function) and optimization will be interesting work but should
probably done last (also currently an empty stub function).

I hope others will start taking a look and even try to take on some of
this.  If interested, the relevant files are all in the Engine folder:

new_orc_parser.c (recommend to start looking here)
csound.l
csound.y
csound_orc_compile.c
csound_orc_semantics.c
csound_orc_expressions.c
csound_orc_optimize.c

Also, I had created a simple test suite in the tests folder that is
using CSD files for tests and a simple test.py python script as the
test harness. (The test harness does not run on windows currently and
there are problems to do so as one can not use &> to redirect all
output as one can on *nix systems, so this will need rewriting to
perhaps use pythons process running commands).

Also, you will need to both compile with the new parser enabled (which
in turn requires GNU flex and bison installed) and also will need to
turn on the new parser when running csound using --new-parser.

Well, that sums up what's going on and I hope others get involved!

Thanks,
steven

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