    sig
      external length : string -> int = "%string_length"
      external get : string -> int -> char = "%string_safe_get"
      external set : string -> int -> char -> unit = "%string_safe_set"
      external create : int -> string = "create_string"
      val make : int -> char -> string
      val copy : string -> string
      val sub : string -> pos:int -> len:int -> string
      val fill : string -> pos:int -> len:int -> char -> unit
      val blit :
        src:string -> src_pos:int -> dst:string -> dst_pos:int -> len:int -> unit
      val concat : sep:string -> string list -> string
      val iter : f:(char -> unit) -> string -> unit
      val escaped : string -> string
      val index : string -> char -> int
      val rindex : string -> char -> int
      val index_from : string -> int -> char -> int
      val rindex_from : string -> int -> char -> int
      val contains : string -> char -> bool
      val contains_from : string -> int -> char -> bool
      val rcontains_from : string -> int -> char -> bool
      val uppercase : string -> string
      val lowercase : string -> string
      val capitalize : string -> string
      val uncapitalize : string -> string
      external unsafe_get : string -> int -> char = "%string_unsafe_get"
      external unsafe_set : string -> int -> char -> unit = "%string_unsafe_set"
      external unsafe_blit :
        src:string -> src_pos:int -> dst:string -> dst_pos:int -> len:int -> unit
        = "blit_string" "noalloc"
      external unsafe_fill : string -> pos:int -> len:int -> char -> unit
        = "fill_string" "noalloc"
    end