bind f inp evaluates to match inp with None -> None | Some x -> f x

binder : 'T -> 'U option

A function that takes the value of type T from an option and transforms it into an option containing a value of type U.

option : 'T option

The input option.

Returns: 'U option

An option of the output type of the binder.

Example

 let tryParse (input: string) =
     match System.Int32.TryParse input with
     | true, v -> Some v
     | false, _ -> None
 None |> Option.bind tryParse // evaluates to None
 Some "42" |> Option.bind tryParse // evaluates to Some 42
 Some "Forty-two" |> Option.bind tryParse // evaluates to None

Evaluates to true if option is Some and its value is equal to value.

value : 'T

The value to test for equality.

option : 'T option

The input option.

Returns: bool

True if the option is Some and contains a value equal to value, otherwise false.

Example

 (99, None) ||> Option.contains // evaluates to false
 (99, Some 99) ||> Option.contains // evaluates to true
 (99, Some 100) ||> Option.contains // evaluates to false

count inp evaluates to match inp with None -> 0 | Some _ -> 1.

option : 'T option

The input option.

Returns: int

A zero if the option is None, a one otherwise.

Example

 None |> Option.count // evaluates to 0
 Some 99 |> Option.count // evaluates to 1

Gets the value of the option if the option is Some, otherwise returns the specified default value.

Identical to the built-in defaultArg operator, except with the arguments swapped.

value : 'T

The specified default value.

option : 'T option

The input option.

Returns: 'T

The option if the option is Some, else the default value.

Example

 (99, None) ||> Option.defaultValue // evaluates to 99
 (99, Some 42) ||> Option.defaultValue // evaluates to 42

Gets the value of the option if the option is Some, otherwise evaluates defThunk and returns the result.

defThunk is not evaluated unless option is None.

defThunk : unit -> 'T

A thunk that provides a default value when evaluated.

option : 'T option

The input option.

Returns: 'T

The option if the option is Some, else the result of evaluating defThunk.

Example

 None |> Option.defaultWith (fun () -> 99) // evaluates to 99
 Some 42 |> Option.defaultWith (fun () -> 99) // evaluates to 42

exists p inp evaluates to match inp with None -> false | Some x -> p x.

predicate : 'T -> bool

A function that evaluates to a boolean when given a value from the option type.

option : 'T option

The input option.

Returns: bool

False if the option is None, otherwise it returns the result of applying the predicate to the option value.

Example

 None |> Option.exists (fun x -> x >= 5) // evaluates to false
 Some 42 |> Option.exists (fun x -> x >= 5) // evaluates to true
 Some 4 |> Option.exists (fun x -> x >= 5) // evaluates to false

filter f inp evaluates to match inp with None -> None | Some x -> if f x then Some x else None.

predicate : 'T -> bool

A function that evaluates whether the value contained in the option should remain, or be filtered out.

option : 'T option

The input option.

Returns: 'T option

The input if the predicate evaluates to true; otherwise, None.

Example

 None |> Option.filter (fun x -> x >= 5) // evaluates to None
 Some 42 |> Option.filter (fun x -> x >= 5) // evaluates to Some 42
 Some 4 |> Option.filter (fun x -> x >= 5) // evaluates to None

flatten inp evaluates to match inp with None -> None | Some x -> x

flatten is equivalent to bind id.

option : 'T option option

The input option.

Returns: 'T option

The input value if the value is Some; otherwise, None.

Example

 (None: int option option) |> Option.flatten // evaluates to None
 (Some ((None: int option))) |> Option.flatten // evaluates to None
 (Some (Some 42)) |> Option.flatten // evaluates to Some 42

fold f s inp evaluates to match inp with None -> s | Some x -> f s x.

folder : 'State -> 'T -> 'State

A function to update the state data when given a value from an option.

state : 'State

The initial state.

option : 'T option

The input option.

Returns: 'State

The original state if the option is None, otherwise it returns the updated state with the folder and the option value.

Example

 (0, None) ||> Option.fold (fun accum x -> accum + x * 2) // evaluates to 0
 (0, Some 1) ||> Option.fold (fun accum x -> accum + x * 2) // evaluates to 2
 (10, Some 1) ||> Option.fold (fun accum x -> accum + x * 2) // evaluates to 12

fold f inp s evaluates to match inp with None -> s | Some x -> f x s.

folder : 'T -> 'State -> 'State

A function to update the state data when given a value from an option.

option : 'T option

The input option.

state : 'State

The initial state.

Returns: 'State

The original state if the option is None, otherwise it returns the updated state with the folder and the option value.

Example

 (None, 0) ||> Option.foldBack (fun x accum -> accum + x * 2) // evaluates to 0
 (Some 1, 0) ||> Option.foldBack (fun x accum -> accum + x * 2) // evaluates to 2
 (Some 1, 10) ||> Option.foldBack (fun x accum -> accum + x * 2) // evaluates to 12

forall p inp evaluates to match inp with None -> true | Some x -> p x.

predicate : 'T -> bool

A function that evaluates to a boolean when given a value from the option type.

option : 'T option

The input option.

Returns: bool

True if the option is None, otherwise it returns the result of applying the predicate to the option value.

Example

 None |> Option.forall (fun x -> x >= 5) // evaluates to true
 Some 42 |> Option.forall (fun x -> x >= 5) // evaluates to true
 Some 4 |> Option.forall (fun x -> x >= 5) // evaluates to false

Gets the value associated with the option.

option : 'T option

The input option.

Returns: 'T

The value within the option.

Example

 Some 42 |> Option.get // evaluates to 42
 (None: int option) |> Option.get // throws exception!

Returns true if the option is None.

option : 'T option

The input option.

Returns: bool

True if the option is None.

Example

 None |> Option.isNone // evaluates to true
 Some 42 |> Option.isNone // evaluates to false

Returns true if the option is not None.

option : 'T option

The input option.

Returns: bool

True if the option is not None.

Example

 None |> Option.isSome // evaluates to false
 Some 42 |> Option.isSome // evaluates to true

iter f inp executes match inp with None -> () | Some x -> f x.

action : 'T -> unit

A function to apply to the option value.

option : 'T option

The input option.

Example

 None |> Option.iter (printfn "%s") // does nothing
 Some "Hello world" |> Option.iter (printfn "%s") // prints "Hello world"

map f inp evaluates to match inp with None -> None | Some x -> Some (f x).

mapping : 'T -> 'U

A function to apply to the option value.

option : 'T option

The input option.

Returns: 'U option

An option of the input value after applying the mapping function, or None if the input is None.

Example

 None |> Option.map (fun x -> x * 2) // evaluates to None
 Some 42 |> Option.map (fun x -> x * 2) // evaluates to Some 84

map f option1 option2 evaluates to match option1, option2 with Some x, Some y -> Some (f x y) | _ -> None.

mapping : 'T1 -> 'T2 -> 'U

A function to apply to the option values.

option1 : 'T1 option

The first option.

option2 : 'T2 option

The second option.

Returns: 'U option

An option of the input values after applying the mapping function, or None if either input is None.

Example

 (None, None) ||> Option.map2 (fun x y -> x + y) // evaluates to None
 (Some 5, None) ||> Option.map2 (fun x y -> x + y) // evaluates to None
 (None, Some 10) ||> Option.map2 (fun x y -> x + y) // evaluates to None
 (Some 5, Some 10) ||> Option.map2 (fun x y -> x + y) // evaluates to Some 15

map f option1 option2 option3 evaluates to match option1, option2, option3 with Some x, Some y, Some z -> Some (f x y z) | _ -> None.

mapping : 'T1 -> 'T2 -> 'T3 -> 'U

A function to apply to the option values.

option1 : 'T1 option

The first option.

option2 : 'T2 option

The second option.

option3 : 'T3 option

The third option.

Returns: 'U option

An option of the input values after applying the mapping function, or None if any input is None.

Example

 (None, None, None) |||> Option.map3 (fun x y z -> x + y + z) // evaluates to None
 (Some 100, None, None) |||> Option.map3 (fun x y z -> x + y + z) // evaluates to None
 (None, Some 100, None) |||> Option.map3 (fun x y z -> x + y + z) // evaluates to None
 (None, None, Some 100) |||> Option.map3 (fun x y z -> x + y + z) // evaluates to None
 (Some 5, Some 100, Some 10) |||> Option.map3 (fun x y z -> x + y + z) // evaluates to Some 115

Convert a Nullable value to an option.

value : Nullable<'T>

The input nullable value.

Returns: 'T option

The result option.

Example

 System.Nullable<int>() |> Option.ofNullable // evaluates to None
 System.Nullable(42) |> Option.ofNullable // evaluates to Some 42

Convert a potentially null value to an option.

value : 'T

The input value.

Returns: 'T option

The result option.

Example

 (null: string) |> Option.ofObj // evaluates to None
 "not a null string" |> Option.ofObj // evaluates to (Some "not a null string")

Returns option if it is Some, otherwise returns ifNone.

ifNone : 'T option

The value to use if option is None.

option : 'T option

The input option.

Returns: 'T option

The option if the option is Some, else the alternate option.

Example

 ((None: int Option), None) ||> Option.orElse // evaluates to None
 (Some 99, None) ||> Option.orElse // evaluates to Some 99
 (None, Some 42) ||> Option.orElse // evaluates to Some 42
 (Some 99, Some 42) ||> Option.orElse // evaluates to Some 42

Returns option if it is Some, otherwise evaluates ifNoneThunk and returns the result.

ifNoneThunk is not evaluated unless option is None.

ifNoneThunk : unit -> 'T option

A thunk that provides an alternate option when evaluated.

option : 'T option

The input option.

Returns: 'T option

The option if the option is Some, else the result of evaluating ifNoneThunk.

Example

 (None: int Option) |> Option.orElseWith (fun () -> None) // evaluates to None
 None |> Option.orElseWith (fun () -> (Some 99)) // evaluates to Some 99
 Some 42 |> Option.orElseWith (fun () -> None) // evaluates to Some 42
 Some 42 |> Option.orElseWith (fun () -> (Some 99)) // evaluates to Some 42

Convert the option to an array of length 0 or 1.

option : 'T option

The input option.

Returns: 'T[]

The result array.

Example

 (None: int option) |> Option.toArray // evaluates to [||]
 Some 42 |> Option.toArray // evaluates to [|42|]

Convert the option to a list of length 0 or 1.

option : 'T option

The input option.

Returns: 'T list

The result list.

Example

 (None: int option) |> Option.toList // evaluates to []
 Some 42 |> Option.toList // evaluates to [42]

Convert the option to a Nullable value.

option : 'T option

The input option.

Returns: Nullable<'T>

The result value.

Example

 (None: int option) |> Option.toNullable // evaluates to new System.Nullable<int>()
 Some 42 |> Option.toNullable // evaluates to new System.Nullable(42)

Convert an option to a potentially null value.

value : 'T option

The input value.

Returns: 'T

The result value, which is null if the input was None.

Example

 (None: string option) |> Option.toObj // evaluates to null
 Some "not a null string" |> Option.toObj // evaluates to "not a null string"