#include <stdio.h>
#include <malloc.h>
#include "/home/comp320/public_html/2005/assignments/support/320bool.h"

/*******************
 * List Type
 *******************/
struct AList {
    int             first;
    struct AList *  rest;
};
typedef  struct AList *  List;

/*******************
 * List Constructors
 *******************/
List
make_empty()
{
    return NULL;
}

List
make_cons(int first, List rest)
{
    List  list = (List) malloc(sizeof(struct AList));
    if (list == NULL) {
	fprintf(stderr,"Out of memory.\n");
	exit(1);
    }
  
    list->first = first;
    list->rest  = rest;

    return list;
}

/*******************
 * List Predicates
 *******************/
bool
is_empty(List list)
{
    return (list == NULL);
}

bool
is_cons(List list)
{
    return (list != NULL);
}

/*******************
 * List Selectors
 *******************/
int
cons_first(List list)
{
    if (is_cons(list))
	return list->first;
    else {
	/* Must be an empty list. */
	fprintf(stderr,"Can't take the first of an empty list.\n");
	exit(1);
    }
}

List
cons_rest(List list)
{
    if (is_cons(list))
	return list->rest;
    else {
	/* Must be an empty list. */
	fprintf(stderr,"Can't take the rest of an empty list.\n");
	exit(1);
    }
}


/*******************
 * List Destructor
 *******************/

/* Free an entire list.
 * Assume there are no other pointers to anywhere in the list.
 */
void
free_list(list)
{
    if (list != NULL) {
	free_list(cons_rest(list));
	free(list);
    }
}


/*******************
 * List Functions
 *******************/

/* Returns a new list that is the reverse of the input list, appended
 * at the front of the previously accumulated list.
 */
List
reverse_help(List list,
	     List accum)
{
  if (is_empty(list)) {
    return accum;
  }
  else {
    return reverse_help(cons_rest(list),make_cons(cons_first(list),accum));
  }
}

/* Returns a new list that is the reverse of the input list.
 */
List
reverse(List list)
{
  return reverse_help(list,make_empty());
}

/* Prints the elements of input list to standard output.
 * The elements are separated by spaces, and terminated by
 * a space and newline.
 */
void
print_list(List list)
{
  List temp_list;

  for (temp_list = list;
       !is_empty(temp_list);
       temp_list = cons_rest(temp_list)) {
    printf("%d ",cons_first(temp_list));
  }
  putchar('\n');
}


/*******************
 * Main function to print the reversed sample list.
 *******************/
int
main(void)
{
  List list = make_cons(3,make_cons(7,make_cons(9,make_cons(2,make_cons(8,make_empty())))));
  List revlist = reverse(list);
  
  printf("The reverse of   ");
  print_list(list);
  printf("\nis   ");
  print_list(revlist);
  putchar('\n');

  free_list(list);
  free_list(revlist);

  return 0;  /* no error */
}


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