///hasChild(parent, id)
/**
 * hasChild :: TreeNode -> TreeNode -> Boolean
 * 
 * Returns whether `parent` directly contains `id` as a child.
 *
 * @param parent the parent TreeNode
 * @param id the child TreeNode
 * @returns true if id is a child of parent
 */

return ds_list_find_index(argument0.children, argument1);