Batteries user guide : BatString.Exceptionless

`sig val to_int : string -> int option val to_float : string -> float option val index : string -> char -> int option val rindex : string -> char -> int option val index_from : string -> int -> char -> int option val rindex_from : string -> int -> char -> int option val find : string -> string -> int option val find_from : string -> int -> string -> int option val rfind : string -> string -> int option val rfind_from : string -> int -> string -> int option val split : string -> by:string -> (string * string) option val rsplit : string -> by:string -> (string * string) option end`