.TH "Result" 3 2025-06-18 OCamldoc "OCaml library"
.SH NAME
Result \- Result values.
.SH Module
Module   Result
.SH Documentation
.sp
Module
.BI "Result"
 : 
.B sig end

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

.sp
.B "Since"
4.08

.sp

.sp
.sp

.PP
.SS Results

.PP
.I type 
.B ('a, 'e)
.I t 
= 
.B ('a, 'e) result
=
 | Ok
.B of 
.B 'a
 | Error
.B of 
.B 'e
 
.sp
The type for result values\&. Either a value 
.ft B
Ok v
.ft R
or an error 
.ft B
Error e
.ft R
\&.

.sp

.I val ok 
: 
.B 'a -> ('a, 'e) result
.sp

.ft B
ok v
.ft R
is 
.ft B
Ok v
.ft R
\&.

.sp

.I val error 
: 
.B 'e -> ('a, 'e) result
.sp

.ft B
error e
.ft R
is 
.ft B
Error e
.ft R
\&.

.sp

.I val value 
: 
.B ('a, 'e) result -> default:'a -> 'a
.sp

.ft B
value r ~default
.ft R
is 
.ft B
v
.ft R
if 
.ft B
r
.ft R
is 
.ft B
Ok v
.ft R
and 
.ft B
default
.ft R
otherwise\&.

.sp

.I val get_ok 
: 
.B ('a, 'e) result -> 'a
.sp

.ft B
get_ok r
.ft R
is 
.ft B
v
.ft R
if 
.ft B
r
.ft R
is 
.ft B
Ok v
.ft R
and raise otherwise\&.

.sp
.B "Raises Invalid_argument"
if 
.ft B
r
.ft R
is 
.ft B
Error _
.ft R
\&.

.sp

.I val get_ok' 
: 
.B ('a, string) result -> 'a
.sp

.ft B
get_ok\&'
.ft R
is like 
.ft B
Result\&.get_ok
.ft R
but in case of error uses the
error message for raising 
.ft B
Invalid_argument
.ft R
\&.

.sp
.B "Since"
5.4

.sp

.I val get_error 
: 
.B ('a, 'e) result -> 'e
.sp

.ft B
get_error r
.ft R
is 
.ft B
e
.ft R
if 
.ft B
r
.ft R
is 
.ft B
Error e
.ft R
and raise otherwise\&.

.sp
.B "Raises Invalid_argument"
if 
.ft B
r
.ft R
is 
.ft B
Ok _
.ft R
\&.

.sp

.I val error_to_failure 
: 
.B ('a, string) result -> 'a
.sp

.ft B
error_to_failure r
.ft R
is 
.ft B
v
.ft R
if 
.ft B
r
.ft R
is 
.ft B
Ok v
.ft R
and raises 
.ft B
Failure e
.ft R
if 
.ft B
r
.ft R
is 
.ft B
Error e
.ft R
\&.

.sp
.B "Since"
5.4

.sp

.I val bind 
: 
.B ('a, 'e) result ->
.B   ('a -> ('b, 'e) result) -> ('b, 'e) result
.sp

.ft B
bind r f
.ft R
is 
.ft B
f v
.ft R
if 
.ft B
r
.ft R
is 
.ft B
Ok v
.ft R
and 
.ft B
r
.ft R
if 
.ft B
r
.ft R
is 
.ft B
Error _
.ft R
\&.

.sp

.I val join 
: 
.B (('a, 'e) result, 'e) result -> ('a, 'e) result
.sp

.ft B
join rr
.ft R
is 
.ft B
r
.ft R
if 
.ft B
rr
.ft R
is 
.ft B
Ok r
.ft R
and 
.ft B
rr
.ft R
if 
.ft B
rr
.ft R
is 
.ft B
Error _
.ft R
\&.

.sp

.I val map 
: 
.B ('a -> 'b) -> ('a, 'e) result -> ('b, 'e) result
.sp

.ft B
map f r
.ft R
is 
.ft B
Ok (f v)
.ft R
if 
.ft B
r
.ft R
is 
.ft B
Ok v
.ft R
and 
.ft B
r
.ft R
if 
.ft B
r
.ft R
is 
.ft B
Error _
.ft R
\&.

.sp

.I val product 
: 
.B ('a, 'e) result ->
.B   ('b, 'e) result -> ('a * 'b, 'e) result
.sp

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

.sp
.B "Since"
5.4

.sp

.I val map_error 
: 
.B ('e -> 'f) -> ('a, 'e) result -> ('a, 'f) result
.sp

.ft B
map_error f r
.ft R
is 
.ft B
Error (f e)
.ft R
if 
.ft B
r
.ft R
is 
.ft B
Error e
.ft R
and 
.ft B
r
.ft R
if
.ft B
r
.ft R
is 
.ft B
Ok _
.ft R
\&.

.sp

.I val fold 
: 
.B ok:('a -> 'c) -> error:('e -> 'c) -> ('a, 'e) result -> 'c
.sp

.ft B
fold ~ok ~error r
.ft R
is 
.ft B
ok v
.ft R
if 
.ft B
r
.ft R
is 
.ft B
Ok v
.ft R
and 
.ft B
error e
.ft R
if 
.ft B
r
.ft R
is 
.ft B
Error e
.ft R
\&.

.sp

.I val retract 
: 
.B ('a, 'a) result -> 'a
.sp

.ft B
retract r
.ft R
is 
.ft B
v
.ft R
if 
.ft B
r
.ft R
is 
.ft B
Ok v
.ft R
or 
.ft B
Error v
.ft R
\&.

.sp
.B "Since"
5.4

.sp

.I val iter 
: 
.B ('a -> unit) -> ('a, 'e) result -> unit
.sp

.ft B
iter f r
.ft R
is 
.ft B
f v
.ft R
if 
.ft B
r
.ft R
is 
.ft B
Ok v
.ft R
and 
.ft B
()
.ft R
otherwise\&.

.sp

.I val iter_error 
: 
.B ('e -> unit) -> ('a, 'e) result -> unit
.sp

.ft B
iter_error f r
.ft R
is 
.ft B
f e
.ft R
if 
.ft B
r
.ft R
is 
.ft B
Error e
.ft R
and 
.ft B
()
.ft R
otherwise\&.

.sp

.PP
.SS Predicates and comparisons

.PP

.I val is_ok 
: 
.B ('a, 'e) result -> bool
.sp

.ft B
is_ok r
.ft R
is 
.ft B
true
.ft R
if and only if 
.ft B
r
.ft R
is 
.ft B
Ok _
.ft R
\&.

.sp

.I val is_error 
: 
.B ('a, 'e) result -> bool
.sp

.ft B
is_error r
.ft R
is 
.ft B
true
.ft R
if and only if 
.ft B
r
.ft R
is 
.ft B
Error _
.ft R
\&.

.sp

.I val equal 
: 
.B ok:('a -> 'a -> bool) ->
.B   error:('e -> 'e -> bool) ->
.B   ('a, 'e) result -> ('a, 'e) result -> bool
.sp

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

.sp

.I val compare 
: 
.B ok:('a -> 'a -> int) ->
.B   error:('e -> 'e -> int) ->
.B   ('a, 'e) result -> ('a, 'e) result -> int
.sp

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

.sp

.PP
.SS Converting

.PP

.I val to_option 
: 
.B ('a, 'e) result -> 'a option
.sp

.ft B
to_option r
.ft R
is 
.ft B
r
.ft R
as an option, mapping 
.ft B
Ok v
.ft R
to 
.ft B
Some v
.ft R
and
.ft B
Error _
.ft R
to 
.ft B
None
.ft R
\&.

.sp

.I val to_list 
: 
.B ('a, 'e) result -> 'a list
.sp

.ft B
to_list r
.ft R
is 
.ft B
[v]
.ft R
if 
.ft B
r
.ft R
is 
.ft B
Ok v
.ft R
and 
.ft B
[]
.ft R
otherwise\&.

.sp

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

.ft B
to_seq r
.ft R
is 
.ft B
r
.ft R
as a sequence\&. 
.ft B
Ok v
.ft R
is the singleton sequence
containing 
.ft B
v
.ft R
and 
.ft B
Error _
.ft R
is the empty sequence\&.

.sp

.PP
.SS Syntax

.PP
.I module Syntax : 
.B sig end

.sp
Binding operators\&. See manual section 12\&.23 for details\&.

.sp
.B "Since"
5.4

.sp