DESIGN subcommand in GLM

[Jason Stover]

I'm thinking about how to write the parser for the DESIGN
subcommand. My question is where to start reading. I have been reading
the code in lexer.c and variable-parser.c.  Before I dive in, I just
want to know if I'm looking in the right place.

An example of the use of the DESIGN subcommand might look like this:

DESIGN A, B, A*D

...which tells me the design matrix should have a column for the
variable A, a column for the variable B, and columns for an
interaction between variables A and D. Another possibility
is 

DESIGN A, B, A(B)

...which tells me the variable A is "nested" in the variable B
(which sounds backwards, but that's the notation).

To write the parser, should I be looking at something like lex_get,
or is there a set of higher-level functions that will do the job?

-Jason