Nested functions in GNU C

nested.c

#include <stdio.h>
#include <assert.h>

#define defer_(x) \
    ({ typeof(x) fun(void) { return x; } fun; })

#define defer(n, x) \
    typeof(x) (*n)() = defer_(x)

int main(void)
{
    int a = 42;

    defer (t1, printf("World\n"));
    defer (t2, 1+2);
    defer (t3, a++);

    printf("Hello ");
    t1();

    assert(t2() == 3);
    assert((t3(), a) == 43);

    return 0;
}