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Module Result

Result is often used to handle error messages.

Signature

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.

val compare : ('ok -> 'ok -> int) -> ('err -> 'err -> int) -> ('ok, 'err) t -> ('ok, 'err) t -> int
val t_of_sexp : (Sexplib.Sexp.t -> 'ok) -> (Sexplib.Sexp.t -> 'err) -> Sexplib.Sexp.t -> ('ok, 'err) t
val sexp_of_t : ('ok -> Sexplib.Sexp.t) -> ('err -> Sexplib.Sexp.t) -> ('ok, 'err) t -> Sexplib.Sexp.t
val bin_t : 'ok Bin_prot.Type_class.t -> 'err Bin_prot.Type_class.t -> ('ok, 'err) t Bin_prot.Type_class.t
val bin_read_t : 'ok Bin_prot.Read.reader -> 'err Bin_prot.Read.reader -> ('ok, 'err) t Bin_prot.Read.reader
val __bin_read_t__ : 'ok Bin_prot.Read.reader -> 'err Bin_prot.Read.reader -> (int -> ('ok, 'err) t) Bin_prot.Read.reader
val bin_size_t : 'ok Bin_prot.Size.sizer -> 'err Bin_prot.Size.sizer -> ('ok, 'err) t Bin_prot.Size.sizer
val bin_write_t : 'ok Bin_prot.Write.writer -> 'err Bin_prot.Write.writer -> ('ok, 'err) t Bin_prot.Write.writer
include Monad.S2 with type ('a, 'err) t := ('a, 'err) t
type ('a, 'e) t
include Monad_intf.Infix2 with type ('a, 'e) t := ('a, 'e) t
type ('a, 'e) t
val (>>=) : ('a, 'e) t -> ('a -> ('b, 'e) t) -> ('b, 'e) t
val (>>|) : ('a, 'e) t -> ('a -> 'b) -> ('b, 'e) t
include Monad_intf.Syntax2 with type ('a, 'e) t := ('a, 'e) t
type ('a, 'e) t
module Let_syntax : sig .. end
module Monad_infix : Monad_intf.Infix2 with type ('a, 'e) t := ('a, 'e) t
val bind : ('a, 'e) t -> ('a -> ('b, 'e) t) -> ('b, 'e) t
val return : 'a -> ('a, _) t
val map : ('a, 'e) t -> f:('a -> 'b) -> ('b, 'e) t
val join : (('a, 'e) t, 'e) t -> ('a, 'e) t
val ignore_m : (_, 'e) t -> (unit, 'e) t
val all : ('a, 'e) t list -> ('a list, 'e) t
val all_ignore : (unit, 'e) t list -> (unit, 'e) t
val ignore : (_, 'err) t -> (unit, 'err) t
val fail : 'err -> (_, 'err) t
val failf : ('a, unit, string, (_, string) t) Pervasives.format4 -> 'a

e.g. failf "Couldn't find bloogle %s" (Bloogle.to_string b)

val is_ok : (_, _) t -> bool
val is_error : (_, _) t -> bool
val ok : ('ok, _) t -> 'ok option
val error : (_, 'err) t -> 'err option
val of_option : 'ok option -> error:'err -> ('ok, 'err) t
val iter : ('ok, _) t -> f:('ok -> unit) -> unit
val iter_error : (_, '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

Returns Ok if both are Ok and Error otherwise.

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

ok_if_true returns Ok () if bool is true, and Error error if it is false

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

raises Failure in the Error case

val ok_unit : (unit, _) t

ok_unit = Ok (), used to avoid allocation as a performance hack

module Export : sig .. end
module Stable : sig .. end