#ifndef _STACK_H
#define _STACK_H 1

#include <stdlib.h>

typedef struct s_stack *pile_t;

struct s_stack {
  pile_t next;
  void* data;
};

#define empty_stack() (NULL)
#define stack_is_empty(s) (!(s))

pile_t push(void* x, pile_t s);
void* pop(pile_t *s);

#endif