.TH "Option" 3 2024-05-31 OCamldoc "OCaml library"
.SH NAME
Option \- Option values.
.SH Module
Module   Option
.SH Documentation
.sp
Module
.BI "Option"
 : 
.B sig end

.sp
Option values\&.
.sp
Option values explicitly indicate the presence or absence of a value\&.

.sp
.B "Since"
4.08

.sp

.sp
.sp

.PP
.SS Options

.PP
.I type 
.B 'a
.I t 
= 
.B 'a option
=
 | None
 | Some
.B of 
.B 'a
 
.sp
The type for option values\&. Either 
.ft B
None
.ft R
or a value 
.ft B
Some v
.ft R
\&.

.sp

.I val none 
: 
.B 'a option
.sp

.ft B
none
.ft R
is 
.ft B
None
.ft R
\&.

.sp

.I val some 
: 
.B 'a -> 'a option
.sp

.ft B
some v
.ft R
is 
.ft B
Some v
.ft R
\&.

.sp

.I val value 
: 
.B 'a option -> default:'a -> 'a
.sp

.ft B
value o ~default
.ft R
is 
.ft B
v
.ft R
if 
.ft B
o
.ft R
is 
.ft B
Some v
.ft R
and 
.ft B
default
.ft R
otherwise\&.

.sp

.I val get 
: 
.B 'a option -> 'a
.sp

.ft B
get o
.ft R
is 
.ft B
v
.ft R
if 
.ft B
o
.ft R
is 
.ft B
Some v
.ft R
and raise otherwise\&.

.sp
.B "Raises Invalid_argument"
if 
.ft B
o
.ft R
is 
.ft B
None
.ft R
\&.

.sp

.I val bind 
: 
.B 'a option -> ('a -> 'b option) -> 'b option
.sp

.ft B
bind o f
.ft R
is 
.ft B
f v
.ft R
if 
.ft B
o
.ft R
is 
.ft B
Some v
.ft R
and 
.ft B
None
.ft R
if 
.ft B
o
.ft R
is 
.ft B
None
.ft R
\&.

.sp

.I val join 
: 
.B 'a option option -> 'a option
.sp

.ft B
join oo
.ft R
is 
.ft B
Some v
.ft R
if 
.ft B
oo
.ft R
is 
.ft B
Some (Some v)
.ft R
and 
.ft B
None
.ft R
otherwise\&.

.sp

.I val map 
: 
.B ('a -> 'b) -> 'a option -> 'b option
.sp

.ft B
map f o
.ft R
is 
.ft B
None
.ft R
if 
.ft B
o
.ft R
is 
.ft B
None
.ft R
and 
.ft B
Some (f v)
.ft R
if 
.ft B
o
.ft R
is 
.ft B
Some v
.ft R
\&.

.sp

.I val fold 
: 
.B none:'a -> some:('b -> 'a) -> 'b option -> 'a
.sp

.ft B
fold ~none ~some o
.ft R
is 
.ft B
none
.ft R
if 
.ft B
o
.ft R
is 
.ft B
None
.ft R
and 
.ft B
some v
.ft R
if 
.ft B
o
.ft R
is
.ft B
Some v
.ft R
\&.

.sp

.I val iter 
: 
.B ('a -> unit) -> 'a option -> unit
.sp

.ft B
iter f o
.ft R
is 
.ft B
f v
.ft R
if 
.ft B
o
.ft R
is 
.ft B
Some v
.ft R
and 
.ft B
()
.ft R
otherwise\&.

.sp

.PP
.SS Predicates and comparisons

.PP

.I val is_none 
: 
.B 'a option -> bool
.sp

.ft B
is_none o
.ft R
is 
.ft B
true
.ft R
if and only if 
.ft B
o
.ft R
is 
.ft B
None
.ft R
\&.

.sp

.I val is_some 
: 
.B 'a option -> bool
.sp

.ft B
is_some o
.ft R
is 
.ft B
true
.ft R
if and only if 
.ft B
o
.ft R
is 
.ft B
Some o
.ft R
\&.

.sp

.I val equal 
: 
.B ('a -> 'a -> bool) -> 'a option -> 'a option -> bool
.sp

.ft B
equal eq o0 o1
.ft R
is 
.ft B
true
.ft R
if and only if 
.ft B
o0
.ft R
and 
.ft B
o1
.ft R
are both 
.ft B
None
.ft R
or if they are 
.ft B
Some v0
.ft R
and 
.ft B
Some v1
.ft R
and 
.ft B
eq v0 v1
.ft R
is 
.ft B
true
.ft R
\&.

.sp

.I val compare 
: 
.B ('a -> 'a -> int) -> 'a option -> 'a option -> int
.sp

.ft B
compare cmp o0 o1
.ft R
is a total order on options using 
.ft B
cmp
.ft R
to compare
values wrapped by 
.ft B
Some _
.ft R
\&. 
.ft B
None
.ft R
is smaller than 
.ft B
Some _
.ft R
values\&.

.sp

.PP
.SS Converting

.PP

.I val to_result 
: 
.B none:'e -> 'a option -> ('a, 'e) result
.sp

.ft B
to_result ~none o
.ft R
is 
.ft B
Ok v
.ft R
if 
.ft B
o
.ft R
is 
.ft B
Some v
.ft R
and 
.ft B
Error none
.ft R
otherwise\&.

.sp

.I val to_list 
: 
.B 'a option -> 'a list
.sp

.ft B
to_list o
.ft R
is 
.ft B
[]
.ft R
if 
.ft B
o
.ft R
is 
.ft B
None
.ft R
and 
.ft B
[v]
.ft R
if 
.ft B
o
.ft R
is 
.ft B
Some v
.ft R
\&.

.sp

.I val to_seq 
: 
.B 'a option -> 'a Seq.t
.sp

.ft B
to_seq o
.ft R
is 
.ft B
o
.ft R
as a sequence\&. 
.ft B
None
.ft R
is the empty sequence and
.ft B
Some v
.ft R
is the singleton sequence containing 
.ft B
v
.ft R
\&.

.sp