#include	"defs.h"

chkhd(head, modes)
	DL	head;
	STRING	modes;
{
	if(head==0 || any(head->type, modes)==0)
		error("context error");
}

/*
 * Require that argument be non-zero.
 *
 * return = argument value; error if zero
 */
must(c)
{
	if(c!=SP)
		error("cursor required");
}

notnil(h)
	DL	h;
{
	if(h==0)
		error("no current item");
}