module Either: sig .. end
Either type.
Either is the simplest and most generic sum/variant type:
a value of ('a, 'b) Either.t
is either a Left (v : 'a)
or a Right (v : 'b)
.
It is a natural choice in the API of generic functions where values could fall in two different cases, possibly at different types, without assigning a specific meaning to what each case should be.
For example:
List.partition_map: ('a -> ('b, 'c) Either.t) -> 'a list -> 'b list * 'c list
If you are looking for a parametrized type where
one alternative means success and the other means failure,
you should use the more specific type Result.t
.
type ('a, 'b) t =
| |
Left of 'a |
| |
Right of 'b |
A value of ('a, 'b) Either.t
contains
either a value of 'a
or a value of 'b
let left: 'a => t('a, 'b);
left v
is Left v
.
let right: 'b => t('a, 'b);
right v
is Right v
.
let is_left: t('a, 'b) => bool;
is_left (Left v)
is true
, is_left (Right v)
is false
.
let is_right: t('a, 'b) => bool;
is_right (Left v)
is false
, is_right (Right v)
is true
.
let find_left: t('a, 'b) => option('a);
find_left (Left v)
is Some v
, find_left (Right _)
is None
let find_right: t('a, 'b) => option('b);
find_right (Right v)
is Some v
, find_right (Left _)
is None
let map_left: ('a1 => 'a2, t('a1, 'b)) => t('a2, 'b);
map_left f e
is Left (f v)
if e
is Left v
and e
if e
is Right _
.
let map_right: ('b1 => 'b2, t('a, 'b1)) => t('a, 'b2);
map_right f e
is Right (f v)
if e
is Right v
and e
if e
is Left _
.
let map: (~left: 'a1 => 'a2, ~right: 'b1 => 'b2, t('a1, 'b1)) => t('a2, 'b2);
map ~left ~right (Left v)
is Left (left v)
,
map ~left ~right (Right v)
is Right (right v)
.
let fold: (~left: 'a => 'c, ~right: 'b => 'c, t('a, 'b)) => 'c;
fold ~left ~right (Left v)
is left v
, and
fold ~left ~right (Right v)
is right v
.
let iter: (~left: 'a => unit, ~right: 'b => unit, t('a, 'b)) => unit;
iter ~left ~right (Left v)
is left v
, and
iter ~left ~right (Right v)
is right v
.
let for_all: (~left: 'a => bool, ~right: 'b => bool, t('a, 'b)) => bool;
for_all ~left ~right (Left v)
is left v
, and
for_all ~left ~right (Right v)
is right v
.
let equal:
(
~left: ('a, 'a) => bool,
~right: ('b, 'b) => bool,
t('a, 'b),
t('a, 'b)
) =>
bool;
equal ~left ~right e0 e1
tests equality of e0
and e1
using left
and right
to respectively compare values wrapped by Left _
and
Right _
.
let compare:
(~left: ('a, 'a) => int, ~right: ('b, 'b) => int, t('a, 'b), t('a, 'b)) =>
int;
compare ~left ~right e0 e1
totally orders e0
and e1
using left
and
right
to respectively compare values wrapped by Left _
and Right _
.
Left _
values are smaller than Right _
values.