#include <stdio.h>
#include "sllist.h"


Sllist new_sllist()
{
  Sllist l;

  l = (Sllist) malloc(sizeof(struct sllist));
  l->link = l;
  return l;
}

free_sllist(Sllist l)
{
  Sllist tmp;

  while (!sll_empty(l)) {
    tmp = sll_first(l);
    l->link = tmp->link;
    free(tmp);
  }
  free(l);
}

Sllist sll_prepend(Sllist l, Jval val)
{
  Sllist tmp;

  return sll_insert_after(l, val);
}


Sllist sll_insert_after(Sllist l, Jval val)
{
  Sllist tmp;

  tmp = (Sllist) malloc(sizeof(struct sllist));
  tmp->val = val;
  tmp->link = l->link;
  l->link = tmp;
  return tmp;
}

Sllist sll_first(Sllist l)
{
  return l->link;
}

Sllist sll_next(Sllist l)
{
  return l->link;
}

Sllist sll_nil(Sllist l)
{
  return l;
}

int sll_empty(Sllist l)
{
  return (l->link == l);
}