> I'm using a recursive descent parser (or a table driven?), it's easy to
make.
> The real problem is run-time library. PIC microcontroller haven't a stack
> area, so there are some problem to pass variables and manage the free
> register.


There is often an assumption that C needs a stack frame for locals or
argument passing. There is nothing in the language that dictates this. One
of the reasons that C as a language is popular is that it maps quite well
on many different processor architectures.

A lot of the recent work we have been doing with C tools for
embedded systems has shown that C can have diverse memory spaces
far more than Harvard architecture processors have. We have shown that
Locals and argument passing can be handled in ways unique to each
processor and the resulting compilers can pass both standard C
conformance tests and portability tests.


Walter Banks