#include <stdio.h>

typedef struct lnode { 
  struct lnode *next;
  void *obj;
} ListNode;

typedef struct {
  ListNode *head;
} List;

void ListNew(List *list) {
  list->head = NULL;
}

void ListAdd(List *list, ListNode *node) {
  if (node == NULL) return;
  node->next = list->head;
  list->head = node;
}

typedef void(*F1)(void*);

void ListPrint(List *list, F1 f) {
  ListNode *p;
  for (p = list->head; p != NULL; p=p->next)
    f(p->obj);
}

typedef struct {
    char *name;
    int age;
} Person;

void PersonPrint(Person *p) {
  printf("%s is %d years old\n", p->name, p->age);  
}

int main() {
    Person john = {
      .name = "John",
      .age = 40
    };
    Person mary = {
      .name = "Mary",
      .age = 32
    };
    Person george = {
      .name = "George",
      .age = 26
    };
    ListNode jnode = { .obj=&john, .next=NULL };
    ListNode mnode = { .obj=&mary, .next=NULL };
    ListNode gnode = { .obj=&george, .next=NULL };
    List list;
    ListNew(&list);
    ListAdd(&list, &jnode);
    ListAdd(&list, &mnode);
    ListAdd(&list, &gnode);
    ListPrint(&list, (F1) PersonPrint);
    return 0;
}