macro-turing-complete.cpp

#define EMPTY0()
#define EMPTY1() EMPTY0 EMPTY0() ()
#define EMPTY() EMPTY1 EMPTY1() ()

#define DEFER(id) id EMPTY()
#define EXPAND(...) __VA_ARGS__


#define INC(x) INC_##x

#define INC_0 1
#define INC_1 2
#define INC_2 3
#define INC_3 4
#define INC_4 5
#define INC_5 6
#define INC_6 7
#define INC_7 8
#define INC_8 9


#define DEC(x) DEC_##x

#define DEC_0 0
#define DEC_1 0
#define DEC_2 1
#define DEC_3 2
#define DEC_4 3
#define DEC_5 4
#define DEC_6 5
#define DEC_7 6
#define DEC_8 7
#define DEC_9 8



///

#define NOT(x) NOT_##x

#define NOT_0 1
#define NOT_1 0

/// 
///
///

#define CAT(a, ...) a ## __VA_ARGS__ //

#define IF(cond, if_true, if_false) CAT(IF_, cond) (if_true, if_false)

#define IF_0(x, y) y
#define IF_1(x, y) x



///
///

#define CHECK_N(x, n, ...) n
#define CHECK(...) CHECK_N(__VA_ARGS__, 0,)
#define IS_ZERO(x) CHECK(CAT(IS_ZERO_, x)) //  ~, 1, 1   IS_ZERO_5, 0

#define IS_ZERO_0 ~, 1
///


///
#define EVAL0(...) __VA_ARGS__
#define EVAL1(...) EVAL0 (EVAL0 (EVAL0 (__VA_ARGS__)))
#define EVAL2(...) EVAL1 (EVAL1 (EVAL1 (__VA_ARGS__)))
#define EVAL3(...) EVAL2 (EVAL2 (EVAL2 (__VA_ARGS__)))
#define EVAL4(...) EVAL3 (EVAL3 (EVAL3 (__VA_ARGS__)))
#define EVAL(...)  EVAL4 (EVAL4 (EVAL4 (__VA_ARGS__)))

///
#define ADD_(x, y) IF(IS_ZERO(x), y, DEFER(ADD_BACK_)  (DEC(x), INC(y)))
#define ADD_BACK_(x,y) IF(IS_ZERO(x), y, DEFER(ADD_) (DEC(x), INC(y)))

#define ADD(x, y) EVAL(ADD_(x, y))


#define TO_STR_(x) #x
#define TO_STR(x) TO_STR_(x)

extern "C" {
    int puts(const char* str);
}

int main() {
    puts(TO_STR(ADD(1, 2)));
    puts(TO_STR(ADD(4, 2)));
}