1Option(3)                        OCaml library                       Option(3)
2
3
4

NAME

6       Option - Option values.
7

Module

9       Module   Option
10

Documentation

12       Module Option
13        : sig end
14
15
16       Option values.
17
18       Option values explicitly indicate the presence or absence of a value.
19
20
21       Since 4.08
22
23
24
25
26
27
28
29   Options
30       type 'a t = 'a option =
31        | None
32        | Some of 'a
33
34
35       The type for option values. Either None or a value Some v .
36
37
38
39       val none : 'a option
40
41
42       none is None .
43
44
45
46       val some : 'a -> 'a option
47
48
49       some v is Some v .
50
51
52
53       val value : 'a option -> default:'a -> 'a
54
55
56       value o ~default is v if o is Some v and default otherwise.
57
58
59
60       val get : 'a option -> 'a
61
62
63       get o is v if o is Some v and
64
65
66       Raises Invalid_argument otherwise.
67
68
69
70       val bind : 'a option -> ('a -> 'b option) -> 'b option
71
72
73       bind o f is f v if o is Some v and None if o is None .
74
75
76
77       val join : 'a option option -> 'a option
78
79
80       join oo is Some v if oo is Some (Some v) and None otherwise.
81
82
83
84       val map : ('a -> 'b) -> 'a option -> 'b option
85
86
87       map f o is None if o is None and Some (f v) is o is Some v .
88
89
90
91       val fold : none:'a -> some:('b -> 'a) -> 'b option -> 'a
92
93
94       fold ~none ~some o is none if o is None and some v if o is Some v .
95
96
97
98       val iter : ('a -> unit) -> 'a option -> unit
99
100
101       iter f o is f v if o is Some v and () otherwise.
102
103
104
105
106   Predicates and comparisons
107       val is_none : 'a option -> bool
108
109
110       is_none o is true iff o is None .
111
112
113
114       val is_some : 'a option -> bool
115
116
117       is_some o is true iff o is Some o .
118
119
120
121       val equal : ('a -> 'a -> bool) -> 'a option -> 'a option -> bool
122
123
124       equal  eq o0 o1 is true iff o0 and o1 are both None or if they are Some
125       v0 and Some v1 and eq v0 v1 is true .
126
127
128
129       val compare : ('a -> 'a -> int) -> 'a option -> 'a option -> int
130
131
132       compare cmp o0 o1 is a total order on options using cmp to compare val‐
133       ues wrapped by Some _ .  None is smaller than Some _ values.
134
135
136
137
138   Converting
139       val to_result : none:'e -> 'a option -> ('a, 'e) result
140
141
142       to_result ~none o is Ok v if o is Some v and Error none otherwise.
143
144
145
146       val to_list : 'a option -> 'a list
147
148
149       to_list o is [] if o is None and [v] if o is Some v .
150
151
152
153       val to_seq : 'a option -> 'a Seq.t
154
155
156       to_seq  o is o as a sequence.  None is the empty sequence and Some v is
157       the singleton sequence containing v .
158
159
160
161
162
163OCamldoc                          2019-07-30                         Option(3)