type t =
  | Basic of ScTypes.types            (** A direct type *)
  | Formula of formula                (** A formula *)

and formula =
  | Expression of ScTypes.expression  (** A valid expression *)
  | Error of int * UTF8.t             (** When the expression cannot be parsed *)


(** Load an expression *)
val load: UTF8.t -> t

val load_expr: t -> t

val is_defined: t -> bool

(** Evaluate the expression *)
val eval: t -> (ScTypes.refs -> ScTypes.types) -> ScTypes.result

(** Collect all the cell referenced in the expression *)
val collect_sources: t -> Cell.Set.t

(** Represent an expression *)
val show: t -> UTF8.t

val shift: (int * int) -> t -> t

val (=): t -> t -> bool