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Class type
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.
since 4.12
type('a, 'b) t =
| Leftof'a
| Rightof'b
A value of ('a, 'b) Either.t contains either a value of 'a or a value of 'b
map_left f e is Left (f v) if e is Left v and e if e is Right _.
val map_right : ('b1->'b2)->('a, 'b1)t->('a, 'b2)t
map_right f e is Right (f v) if e is Right v and e if e is Left _.
val map :
left:('a1->'a2)->right:('b1->'b2)->('a1, 'b1)t->('a2, 'b2)t
map ~left ~right (Left v) is Left (left v), map ~left ~right (Right v) is Right (right v).
val fold : left:('a->'c)->right:('b->'c)->('a, 'b)t->'c
fold ~left ~right (Left v) is left v, and fold ~left ~right (Right v) is right v.
val iter : left:('a-> unit)->right:('b-> unit)->('a, 'b)t-> unit
iter ~left ~right (Left v) is left v, and iter ~left ~right (Right v) is right v.
val for_all : left:('a-> bool)->right:('b-> bool)->('a, 'b)t-> bool
for_all ~left ~right (Left v) is left v, and for_all ~left ~right (Right v) is right v.
val equal :
left:('a->'a-> bool)->right:('b->'b-> bool)->('a, 'b)t->('a, 'b)t->
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 _.
val compare :
left:('a->'a-> int)->right:('b->'b-> int)->('a, 'b)t->('a, 'b)t->
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.