Preprocessor foreach

preprocessor.foreach.cpp

#define EMPTY()
#define DEFER(func) func EMPTY()

#define EVAL(...)  EVAL1(EVAL1(EVAL1(__VA_ARGS__)))
#define EVAL1(...) EVAL2(EVAL2(EVAL2(__VA_ARGS__)))
#define EVAL2(...) EVAL3(EVAL3(EVAL3(__VA_ARGS__)))
#define EVAL3(...) EVAL4(EVAL4(EVAL4(__VA_ARGS__)))
#define EVAL4(...) EVAL5(EVAL5(EVAL5(__VA_ARGS__)))
#define EVAL5(...) __VA_ARGS__

#define PRIMITIVE_CAT(a, ...) a ## __VA_ARGS__
#define IIF(c) PRIMITIVE_CAT(IIF_, c)
#define IIF_0(t, ...) __VA_ARGS__
#define IIF_1(t, ...) t  

#define SECOND(a, b, ...) b
#define IS_PROBE(...) DEFER(SECOND)(__VA_ARGS__, 0)

#define NOT(x) IS_PROBE(_NOT_ ## x)
#define _NOT_0  ~, 1
#define _NOT_   ~, 1


#define FOREACH(METHOD, ...) EVAL(DEFER(FOREACH_CONTINUE)(METHOD, __VA_ARGS__))
#define IF_NOT_ZERO(A) DEFER(IIF)(NOT(A))
#define FOREACH_CONTINUE(METHOD, A, ...) IF_NOT_ZERO(A) (, POP_FIRST(METHOD, A, __VA_ARGS__))

#define POP_FIRST(METHOD, A, ...) METHOD(A) DEFER(POP_FIRST_RESHEDULE)()(METHOD, __VA_ARGS__)
#define POP_FIRST_RESHEDULE() FOREACH_CONTINUE
                       
#define ECHO(a) a +

int f()
{
  int a = FOREACH(ECHO, 1, 2, 3, 4);
}