module BatOption:sig
..end
Options are an Ocaml standard type that can be either None
(undefined)
or Some x
where x can be any value. Options are widely used in Ocaml
to represent undefined values (a little like NULL in C, but in a type
and memory safe way). This module adds some functions for working with
options.
Author(s): Nicolas Cannasse, David Teller
type'a
t ='a option
val may : ('a -> unit) -> 'a option -> unit
may f (Some x)
calls f x
and may f None
does nothing.val map : ('a -> 'b) -> 'a option -> 'b option
map f (Some x)
returns Some (f x)
and map f None
returns None
.val bind : 'a option -> ('a -> 'b option) -> 'b option
bind (Some x) f
returns f x
and bind None f
returns None
.val apply : ('a -> 'a) option -> 'a -> 'a
apply None x
returns x
and apply (Some f) x
returns f x
val filter : ('a -> bool) -> 'a option -> 'a option
filter f None
returns None
, filter f (Some x)
returns Some x
if f x
is true, and None
otherwise.val default : 'a -> 'a option -> 'a
default x (Some v)
returns v
and default x None
returns x
.val (|?) : 'a option -> 'a -> 'a
BatOption.default
, with the arguments reversed.
None |? 10
returns 10
, while Some "foo" |? "bar"
returns "foo"
.
Note This operator does not short circuit like ( || )
and ( && )
.
Both arguments will be evaluated.
Since 2.0
val map_default : ('a -> 'b) -> 'b -> 'a option -> 'b
map_default f x (Some v)
returns f v
and map_default f x None
returns x
.val is_none : 'a option -> bool
is_none None
returns true
otherwise it returns false
.val is_some : 'a option -> bool
is_some (Some x)
returns true
otherwise it returns false
.val get : 'a option -> 'a
get (Some x)
returns x
.Invalid_argument
on get None
.val get_exn : 'a option -> exn -> 'a
get_exn (Some x) e
returns x
and get_exn None e
raises e
.val compare : ?cmp:('a -> 'a -> int) -> 'a option -> 'a option -> int
None
is always assumed to be less than Some _
. The
parameter cmp
defaults to Pervasives.compare
.val eq : ?eq:('a -> 'a -> bool) -> 'a option -> 'a option -> bool
eq
defaults to
Pervasives.(=)
.val enum : 'a option -> 'a BatEnum.t
enum (Some x)
returns the singleton x
, while enum None
returns
the empty enumeration.val of_enum : 'a BatEnum.t -> 'a option
of_enum e
consumes the first element of e
, if it exists, and
returns Some e
. If e
is empty, return None
.module Monad:sig
..end
val print : ('a BatInnerIO.output -> 'b -> unit) ->
'a BatInnerIO.output -> 'b t -> unit
module Labels:sig
..end
module Infix:sig
..end