Result (base.Base_

type ('ok, 'err) t = ('ok, 'err) Pervasives.result =

| Ok of 'ok

| Error of 'err

'ok is a function's expected return type, and 'err 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 sig ... end

val hash_fold_t : (Base__.Ppx_hash_lib.Std.Hash.state ‑> 'ok ‑> Base__.Ppx_hash_lib.Std.Hash.state) ‑> (Base__.Ppx_hash_lib.Std.Hash.state ‑> 'err ‑> Base__.Ppx_hash_lib.Std.Hash.state) ‑> Base__.Ppx_hash_lib.Std.Hash.state ‑> ('ok, 'err) t ‑> Base__.Ppx_hash_lib.Std.Hash.state

val compare : ('ok ‑> 'ok ‑> int) ‑> ('err ‑> 'err ‑> int) ‑> ('ok, 'err) t ‑> ('ok, 'err) t ‑> int

val t_of_sexp : (Base__.Sexplib.Sexp.t ‑> 'ok) ‑> (Base__.Sexplib.Sexp.t ‑> 'err) ‑> Base__.Sexplib.Sexp.t ‑> ('ok, 'err) t

val sexp_of_t : ('ok ‑> Base__.Sexplib.Sexp.t) ‑> ('err ‑> Base__.Sexplib.Sexp.t) ‑> ('ok, 'err) t ‑> Base__.Sexplib.Sexp.t

include Base.Monad.S2 with type (a, err) t := (a, err) t

type ('a, 'e) t

include Base__.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 Base__.Monad_intf.Syntax2 with type (a, e) t := (a, e) t

type ('a, 'e) t

module Let_syntax : sig ... end

module Monad_infix : Base__.Monad_intf.Infix2 with type (a, e) t := (a, e) t

val bind : ('a, 'e) t ‑> f:('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 ok_exn : ('ok, exn) t ‑> 'ok

val ok_or_failwith : ('ok, string) t ‑> 'ok

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