#include <stdio.h>
#include <stdlib.h>

struct point {int x; int y;};
typedef struct point point;

void prnt_point(point p){
  printf("Point: %i, %i\n", p.x, p.y);
}   

struct cons_cell {
  void             *data;
  struct cons_cell *next;
};

typedef struct cons_cell cons_cell;

/* Returns a pointer to a new cons cell, 
   which refers data and next via pointers*/
cons_cell *cons(void *data, cons_cell *next){
 cons_cell *result;
 result = (cons_cell *)malloc(sizeof(cons_cell));
 if (result == NULL){
   printf("Out of memory. Bye.");
   exit(EXIT_FAILURE);
 }
   
 result->data = data;
 result->next = next;
 return result;
}

/* Return the head reference of the cons cell */
void *head(cons_cell *cell){
  return cell->data;
}

/* Return the tail refererence f the cons cell */
cons_cell *tail(cons_cell *cell){
  return cell->next;
}   

/* Change the data position of cell to new_head */
void set_head(cons_cell *cell, void *new_head){
  cell->data = new_head;
}

/* Change the next position of cell to new_tail */
void set_tail(cons_cell *cell, cons_cell *new_tail){
  cell->next = new_tail;
}   




int main(void) {

  cons_cell *points;

  point p1 = {1,2}, p2 = {3,4}, p3 = {5,6};

  points = cons(&p1,
                cons(&p2,
                     cons(&p3,
                          NULL)));

  while (points != NULL) {
    prnt_point(*((point*)(head(points))));
    points = tail(points);
  }
  
  return 0;
}