A "not too much elegant" (and the only) way to get a templated, variadic and type-safe function in pure C

vagenc.c

#include <stdio.h>

#define COUNT(...) (sizeof((int[]){ __VA_ARGS__ })/sizeof(int))

#define __eval(x0, x1, x2, x3, ...) _Generic((x0),              \
    void*: _Generic((x1), int: _evali, double: _evald),         \
    int: _evali,                                                \
    double: _evald                                              \
)(                                                              \
    COUNT(__VA_ARGS__) - _Generic((x0), void *: 1, default: 0), \
    _Generic((x0), void*: (x0), default: NULL),                 \
    _Generic((x0), void*: (x1), default: (x0)),                 \
    _Generic((x0), void*: (x2), default: (x1)),                 \
    _Generic((x0), void*: (x3), default: (x2))                  \
)
#define eval(...) __eval(__VA_ARGS__, 0, 0, 0, 0)

void _evali(size_t c, void* e, int x, int y, int z) {
    if (e) printf("called function with handler and ints: ");
    else printf("called function without handler and ints: ");
    switch(c) {
        case 1: printf("%d\n", x); break;
        case 2: printf("%d %d\n", x, y); break;
        case 3: printf("%d %d %d\n", x, y, z); break;
    }
}

void _evald(size_t c, void* e, double x, double y, double z) {
    if (e) printf("called function with handler and doubles: ");
    else printf("called function without handler and doubles: ");
    switch(c) {
        case 1: printf("%f\n", x); break;
        case 2: printf("%f %f\n", x, y); break;
        case 3: printf("%f %f %f\n", x, y, z); break;
    }
}

int main(int argc, char* argv[]) {
    void* handler = (void*)(&printf);

    eval(1);
    eval(1, 2);
    eval(1, 2, 3);
    eval(handler, 1);
    eval(handler, 1, 2);
    eval(handler, 1, 2, 3);
    eval(1.);
    eval(1., 2.);
    eval(1., 2., 3.);
    eval(handler, 1.);
    eval(handler, 1., 2.);
    eval(handler, 1., 2., 3.);

    return 0;
}