1Either(3)                        OCaml library                       Either(3)
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NAME

6       Either - Either type.
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Module

9       Module   Either
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Documentation

12       Module Either
13        : sig end
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16       Either type.
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18       Either  is  the  simplest and most generic sum/variant type: a value of
19       ('a, 'b) Either.t is either a Left (v : 'a) or a Right (v : 'b) .
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21       It is a natural choice in the API of  generic  functions  where  values
22       could fall in two different cases, possibly at different types, without
23       assigning a specific meaning to what each case should be.
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25       For example:
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28       List.partition_map:
29           ('a -> ('b, 'c) Either.t) -> 'a list -> 'b list * 'c list
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31       If you are looking for a parametrized type where one alternative  means
32       success  and  the other means failure, you should use the more specific
33       type Result.t .
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36       Since 4.12
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42       type ('a, 'b) t =
43        | Left of 'a
44        | Right of 'b
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47       A value of ('a, 'b) Either.t contains either a value of 'a or  a  value
48       of 'b
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53       val left : 'a -> ('a, 'b) t
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56       left v is Left v .
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60       val right : 'b -> ('a, 'b) t
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63       right v is Right v .
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67       val is_left : ('a, 'b) t -> bool
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70       is_left (Left v) is true , is_left (Right v) is false .
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74       val is_right : ('a, 'b) t -> bool
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77       is_right (Left v) is false , is_right (Right v) is true .
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81       val find_left : ('a, 'b) t -> 'a option
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84       find_left (Left v) is Some v , find_left (Right _) is None
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89       val find_right : ('a, 'b) t -> 'b option
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92       find_right (Right v) is Some v , find_right (Left _) is None
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97       val map_left : ('a1 -> 'a2) -> ('a1, 'b) t -> ('a2, 'b) t
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100       map_left f e is Left (f v) if e is Left v and e if e is Right _ .
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104       val map_right : ('b1 -> 'b2) -> ('a, 'b1) t -> ('a, 'b2) t
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107       map_right f e is Right (f v) if e is Right v and e if e is Left _ .
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111       val  map  :  left:('a1 -> 'a2) -> right:('b1 -> 'b2) -> ('a1, 'b1) t ->
112       ('a2, 'b2) t
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115       map ~left ~right (Left v) is Left (left v) , map ~left ~right (Right v)
116       is Right (right v) .
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120       val fold : left:('a -> 'c) -> right:('b -> 'c) -> ('a, 'b) t -> 'c
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123       fold  ~left ~right (Left v) is left v , and fold ~left ~right (Right v)
124       is right v .
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128       val iter : left:('a -> unit) -> right:('b -> unit) ->  ('a,  'b)  t  ->
129       unit
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132       iter  ~left ~right (Left v) is left v , and iter ~left ~right (Right v)
133       is right v .
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137       val for_all : left:('a -> bool) -> right:('b -> bool) -> ('a, 'b) t  ->
138       bool
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141       for_all  ~left  ~right  (Left  v)  is left v , and for_all ~left ~right
142       (Right v) is right v .
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146       val equal : left:('a -> 'a -> bool) -> right:('b -> 'b -> bool) -> ('a,
147       'b) t -> ('a, 'b) t -> bool
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150       equal  ~left  ~right  e0  e1 tests equality of e0 and e1 using left and
151       right to respectively compare values wrapped by Left _ and Right _ .
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155       val compare : left:('a -> 'a -> int) -> right:('b -> 'b -> int) -> ('a,
156       'b) t -> ('a, 'b) t -> int
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159       compare  ~left  ~right  e0  e1  totally orders e0 and e1 using left and
160       right to respectively compare values wrapped by Left _ and  Right  _  .
161       Left _ values are smaller than Right _ values.
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167OCamldoc                          2023-01-23                         Either(3)