module Parameter = struct
  type t =
    | String of string
    | Number of string
    | Special of string
    | Null  (** Possible shell parameters *)
end

module type State = sig
  type t
  (** State for the shell and operating system that is carried from one
      evaluation step to the next. *)

  val cwd : t -> Fpath.t
  (** The current working directory *)

  val set_cwd : t -> Fpath.t -> t
  (** Update the cwd *)

  val expand : t -> [ `Tilde ] -> string
  (** Expansions *)

  val lookup : t -> param:string -> Ast.word_cst option
  (** Parameter lookup. [None] means [unset]. *)

  val update : t -> param:string -> Ast.word_cst -> t
  (** Update the state with a new parameter mapping *)

  val dump : t Fmt.t
end

type redirect =
  | Redirect of int * Eio_unix.Fd.t * Eio_unix.Private.Fork_action.blocking
  | Close of Eio_unix.Fd.t

module type Exec = sig
  type t
  (** An executor for commands *)

  type fork_action
  (** A fork action is a piece of C-code to run inbetween the fork and the exec
  *)

  val exec :
    ?fork_actions:fork_action list ->
    ?fds:redirect list ->
    ?stdin:_ Eio.Flow.source ->
    ?stdout:_ Eio.Flow.sink ->
    ?stderr:_ Eio.Flow.sink ->
    ?env:(string * string) list ->
    cwd:Eio.Fs.dir_ty Eio.Path.t ->
    t ->
    string list ->
    unit Exit.t
  (** Run a command in a child process *)
end