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

#include "stack.h"

struct stack proc_stack;

stack* create_stack(void) {
    stack* s = malloc(sizeof(stack));
    if (!s) exit(-1);
    s->first = NULL;
    return s;
}

void save(void *d, stack *s) {
    stack_elem* elem = malloc(sizeof(stack_elem));
    elem->value = d;

    if (!s->first) {
        elem->next = NULL;
    } else {
        elem->next = s->first;
    }
    s->first = elem;
}

void* restore(stack *s) {
    void *r;
    stack_elem *se;

    if (!s->first) {
        printf("stack empty!\n");
        exit(-1);
    }

    se = s->first;
    r = s->first->value;
    s->first = se->next;
    free(se);
    return r;
}