4.4BSD/usr/src/contrib/jove-4.14.6/list.c

/***************************************************************************
 * This program is Copyright (C) 1986, 1987, 1988 by Jonathan Payne.  JOVE *
 * is provided to you without charge, and with no warranty.  You may give  *
 * away copies of JOVE, including sources, provided that this notice is    *
 * included in all the files.                                              *
 ***************************************************************************/

#include "jove.h"
#include "list.h"

private List *
list_new()
{
	List	*new;

	new = (List *) emalloc(sizeof (List));
	new->car = NULL;
	return new;
}

/* push an object to the beginning of list */

UnivPtr
list_push(list, element)
register List	**list;
UnivPtr element;
{
	List	*new;

	new = list_new();
	new->cdr = *list;
	new->car = element;
	*list = new;
	return element;
}

UnivPtr
list_pop(list)
List	**list;
{
	List	*cell;
	UnivPtr	element;

	if (*list == NULL)
		return NULL;
	cell = *list;
	element = cell->car;
	free((UnivPtr) cell);
	*list = (*list)->cdr;

	return element;
}