Sourceval is_empty : 'a list -> bool Sourceval push_back : 'a -> 'a t -> 'a t Sourceval push_front : 'a -> 'a t -> 'a t Sourceval pop_back_opt : 'a t -> ('a * 'a list) option Sourceval pop_back : 'a t -> 'a * 'a list Sourceval pop_front_opt : 'a t -> ('a * 'a list) option Sourceval pop_front : 'a t -> 'a * 'a list