queue.c

#include "queue.h"
#include "list.h"
#include <stdlib.h>
#include <assert.h>

struct queue
{
  list head;
  list tail;
};

queue queue_create(void)
{
  queue q = malloc(sizeof(struct queue));
  q -> head = q -> tail = NULL;
  return q;
}

int queue_empty(queue q)
{
  return q -> head == NULL;
}

void queue_enq(queue q, void *element)
{
  if(queue_empty(q))
    q -> head = q->tail = cons(element, NULL);
  else
    {
      q->tail->next = cons(element, NULL);
      q->tail = q->tail->next;
    }
}

void *queue_deq(queue q)
{
  assert(!queue_empty(q));
  {
    void *temp = q->head->element;
    q -> head = cdr_and_free(q->head);
    return temp;
  }
}