Result(3)

NAME
Result - Result values.

Module
Module Result

Documentation

Module Result
 : sig end

Result values.

Result values handle computation results and errors in an explicit and declarative manner without resorting to exceptions.

Since 4.08

  Results

type ('a, 'e) t = ('a, 'e) result =
 | Ok of 'a
 | Error of 'e

The type for result values. Either a value Ok v or an error Error e .

val ok : 'a -> ('a, 'e) result

ok v is Ok v .

val error : 'e -> ('a, 'e) result

error e is Error e .

val value : ('a, 'e) result -> default:'a -> 'a

value r ~default is v if r is Ok v and default otherwise.

val get_ok : ('a, 'e) result -> 'a

get_ok r is v if r is Ok v and raise otherwise.

Raises Invalid_argument if r is Error _ .

val get_ok' : ('a, string) result -> 'a

get_ok' is like Result.get_ok but in case of error uses the error message for raising Invalid_argument .

Since 5.4

val get_error : ('a, 'e) result -> 'e

get_error r is e if r is Error e and raise otherwise.

Raises Invalid_argument if r is Ok _ .

val error_to_failure : ('a, string) result -> 'a

error_to_failure r is v if r is Ok v and raises Failure e if r is Error e .

Since 5.4

val bind : ('a, 'e) result -> ('a -> ('b, 'e) result) -> ('b, 'e) result

bind r f is f v if r is Ok v and r if r is Error _ .

val join : (('a, 'e) result, 'e) result -> ('a, 'e) result

join rr is r if rr is Ok r and rr if rr is Error _ .

val map : ('a -> 'b) -> ('a, 'e) result -> ('b, 'e) result

map f r is Ok (f v) if r is Ok v and r if r is Error _ .

val product : ('a, 'e) result -> ('b, 'e) result -> ('a * 'b, 'e) result

product r0 r1 is Ok (v0, v1) if r0 is Ok v0 and r1 is Ok v2 and otherwise returns the error of r0 , if any, or the error of r1 .

Since 5.4

val map_error : ('e -> 'f) -> ('a, 'e) result -> ('a, 'f) result

map_error f r is Error (f e) if r is Error e and r if r is Ok _ .

val fold : ok:('a -> 'c) -> error:('e -> 'c) -> ('a, 'e) result -> 'c

fold ~ok ~error r is ok v if r is Ok v and error e if r is Error e .

val retract : ('a, 'a) result -> 'a

retract r is v if r is Ok v or Error v .

Since 5.4

val iter : ('a -> unit) -> ('a, 'e) result -> unit

iter f r is f v if r is Ok v and () otherwise.

val iter_error : ('e -> unit) -> ('a, 'e) result -> unit

iter_error f r is f e if r is Error e and () otherwise.

  Predicates and comparisons

val is_ok : ('a, 'e) result -> bool

is_ok r is true if and only if r is Ok _ .

val is_error : ('a, 'e) result -> bool

is_error r is true if and only if r is Error _ .

val equal : ok:('a -> 'a -> bool) -> error:('e -> 'e -> bool) -> ('a, 'e) result -> ('a, 'e) result -> bool

equal ~ok ~error r0 r1 tests equality of r0 and r1 using ok and error to respectively compare values wrapped by Ok _ and Error _ .

val compare : ok:('a -> 'a -> int) -> error:('e -> 'e -> int) -> ('a, 'e) result -> ('a, 'e) result -> int

compare ~ok ~error r0 r1 totally orders r0 and r1 using ok and error to respectively compare values wrapped by Ok _ and Error _ . Ok _ values are smaller than Error _ values.

  Converting

val to_option : ('a, 'e) result -> 'a option

to_option r is r as an option, mapping Ok v to Some v and Error _ to None .

val to_list : ('a, 'e) result -> 'a list

to_list r is [v] if r is Ok v and [] otherwise.

val to_seq : ('a, 'e) result -> 'a Seq.t

to_seq r is r as a sequence. Ok v is the singleton sequence containing v and Error _ is the empty sequence.

  Syntax

module Syntax : sig end

Binding operators.

Since 5.4