Potential macro expansion ambiguity in the recursion engine

[Hirrolot]

It seems that the recursion engine relies on one ambiguity in the standard (the issue is about C++ but the C preprocessor is essentially the same):

metalang99/include/metalang99/eval/rec.h

Line 12 in 695a9d8

#define ML99_PRIV_REC_NEXT(next_lvl, choice) ML99_PRIV_REC_NEXT_##choice(next_lvl)

Here, ML99_PRIV_REC_NEXT can expand to ML99_PRIV_REC_<level>, which is then invoked by a caller of ML99_PRIV_REC_NEXT, thus resulting in the ML99_PRIV_REC_NEXT token once again.

However, I haven't noticed any problems with various compilers yet as they seem to treat this ambiguity in the same way. Please, let me know if your compiler doesn't work because of it; to make sure, run tests/eval/rec.c.