Hi All,

Just another update with the new parser.  I got to a point a couple
days ago to be able to compile a simple expression (a single
expression of +, -, /, or *), just to get the basic compilation down.
This is currently being done when an opcode is being compiled from
it's AST representation, so when a node is found that is an expression
it goes and builds opcodes from those expression nodes and prepends
that to the opcode being written.  (For those that haven't looked at
that bit of code, expressions get compiled down as a number of opcode
calls that happen before the opcode that contains the expression, with
the expression replaced with a temp variable).

So, I got to the point where the simple expression works and was going
to move on to implementing the rest of the expression compiling (the
other operators and multiple expression statements) but thought that
this stuff shouldn't be done this way, but rather in an pass over the
AST before it gets to the compilation pass.  Then for each
instruments, all expressions would have been expanded out to opcode
calls, making the compilation a little more straightforward I think.

I am thinking now the stage should be something like
"csound_orc_expand_expressions" and it would happen before
optimization.  The optimization pass would take care of constant
folding (I don't think the current parser does this, so this might be
a possible area where we'll see a little speedup), minimizing number
of temp variables (like doing the same optimization check that current
parser has with not using a temp if the expression is only going to be
assigned to a var and instead use the var as the output to the opcode
call at the end of the expression chain), dead code elimination, etc.
So that'd take us to four passes:

parse
expand_expressions
optimize
compile

If anyone has any thoughts on this I'd love to hear them as I'm still
learning a great deal myself as I'm going along.

Thanks!
steven

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