C Preprocessor - macro expansion

I am having difficulty writing a C preprocessor meeting the ANSI standard.
(Mind you the only preprocessor that I have used that meets the ANSI macro
expansion tests is the GNU gcc). My difficulty lies with macro expansion.
I understand the rules governing the '#' and '##' operators. However in
the collection of arguments and expansion of the macro I am having
difficulty producing a correct algorithm. Consider a paraphrase of the
ANSI tests :




        #define x 2
        #define f(a) f(x * (a))
        #define z z [0]


        f(f(z));


this should macro expand to :


        f(2 * (f(2 * (z [0]))))


my problems arise because each argument of the macro must be fully macro
expanded before use (so f(z) -> f(2 * z [0])) which means I have macro
expanded 'x' and 'z' and this expansion of 'x' prevents the next expansion
of 'x' so currently I end up with f(x * (f(2 * (z [0])))).


I would like to know the steps I have to go through when macro expanding
the above example so as to meet the ANSI provisos :


(i) the replacement sequence is rescanned until all macros have been
        replaced
(ii) once an identifier has been used in a replacement sequence
        it won't be used again


a difficulty with (ii) is illustrated by the (trivial) :


        #define A 12345
        #define abcde A A A A


        abcde


this should macro expand to :


        12345 12345 12345 12345


Thanks for any help/suggestions/elaboration.


P.S. dig out the ANSI tests and try them out on your C preprocessor !
--

Return to the comp.compilers page.
Search the comp.compilers archives again.