module Result: Result
type ('ok, 'err) t =
| |
Ok of 'ok |
| |
Error of 'err |
'a is a function's expected return type, and
'b is often an error message string.
let ric_of_ticker = function
| "IBM" -> Ok "IBM.N"
| "MSFT" -> Ok "MSFT.OQ"
| "AA" -> Ok "AA.N"
| "CSCO" -> Ok "CSCO.OQ"
| _ as ticker -> Error (sprintf "can't find ric of %s" ticker)
The return type of ric_of_ticker could be
string option, but
(string, string)
Result.t gives more control over the error message.
include Sexpable.S2
include Binable.S2
include Monad.S2
val fail : 'err -> ('a, 'err) t
val failf : ('a, unit, string, ('b, string) t) Pervasives.format4 -> 'a
e.g. failf "Couldn't find bloogle %s" (Bloogle.to_string b)
val is_ok : ('a, 'b) t -> bool
val is_error : ('a, 'b) t -> bool
val ok : ('ok, 'a) t -> 'ok option
val error : ('a, 'err) t -> 'err option
val of_option : 'ok option -> error:'err -> ('ok, 'err) t
val iter : ('ok, 'a) t -> f:('ok -> unit) -> unit
val iter_error : ('a, 'err) t -> f:('err -> unit) -> unit
val map : ('ok, 'err) t -> f:('ok -> 'c) -> ('c, 'err) t
val map_error : ('ok, 'err) t -> f:('err -> 'c) -> ('ok, 'c) t
val combine : ('ok1, 'err) t ->
('ok2, 'err) t ->
ok:('ok1 -> 'ok2 -> 'ok3) ->
err:('err -> 'err -> 'err) -> ('ok3, 'err) t
val call : f:('a -> unit, 'b) t -> 'a -> unit
val apply : f:('a -> 'b, 'err) t -> 'a -> ('b, 'err) t
val ok_fst : ('ok, 'err) t -> [ `Fst of 'ok | `Snd of 'err ]
ok_fst is useful with
List.partition_map. Continuing the above example:
let rics, errors = List.partition_map ~f:Result.ok_fst
(List.map ~f:ric_of_ticker ["AA"; "F"; "CSCO"; "AAPL"])
val ok_if_true : bool -> error:'err -> (unit, 'err) t
val try_with : (unit -> 'a) -> ('a, exn) t
val ok_exn : ('ok, exn) t -> 'ok
ok_exn t returns x if t = Ok x, and raises exn if t = Error exn
val ok_or_failwith : ('ok, string) t -> 'ok
val ok_unit : (unit, 'a) t
ok_unit = Ok (), used to avoid allocation as a performance hack
module Export: sig .. end