LISP-like list macros for C

lispy.c

#include <assert.h>
#include <stdlib.h>

#define LIST(a) struct { \
  a     v;               \
  void *n;               \
}

#define CAR(xs) xs->v
#define CDR(xs) xs->n

#define CONS(a, x) do {        \
  void *t = x;                 \
  x       = malloc(sizeof *x); \
                               \
  assert(x != NULL);           \
  x->v = a;                    \
  x->n = t;                    \
} while(0)

#define MAP(f, x) do {  \
  void *t = x;          \
                        \
  while(x != NULL) {    \
    CAR(x) = f(CAR(x)); \
    x = CDR(x);         \
  }                     \
                        \
  if(t) x = t;          \
} while(0)

#include <stdio.h>

int times2(int x) { return x * 2; }

int main() {
  int         i;
  LIST(int) *xs = NULL;
  
  for(i = 10; i > 0; --i)
    CONS(i, xs);
  MAP(times2, xs);
  
  while(xs != NULL) {
    printf("%d -> ", CAR(xs));
    xs = CDR(xs);
  }
  printf("nil\n");
  
  return 0;
}