Result (docs.stdlib.Stdlib.Result)

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 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.