bind f inp evaluates to match inp with ValueNone -> ValueNone | ValueSome x -> f x

binder : 'T -> 'U voption

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

voption : 'T voption

The input value option.

Returns: 'U voption

An option of the output type of the binder.

Example

 let tryParse input =
     match System.Int32.TryParse (input: string) with
     | true, v -> ValueSome v
     | false, _ -> ValueNone
 ValueNone |> ValueOption.bind tryParse // evaluates to ValueNone
 ValueSome "42" |> ValueOption.bind tryParse // evaluates to ValueSome 42
 ValueSome "Forty-two" |> ValueOption.bind tryParse // evaluates to ValueNone

Evaluates to true if voption is ValueSome and its value is equal to value.

value : 'T

The value to test for equality.

voption : 'T voption

The input value option.

Returns: bool

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

Example

 (99, ValueNone) ||> ValueOption.contains // evaluates to false
 (99, ValueSome 99) ||> ValueOption.contains // evaluates to true
 (99, ValueSome 100) ||> ValueOption.contains // evaluates to false

count inp evaluates to match inp with ValueNone -> 0 | ValueSome _ -> 1.

voption : 'T voption

The input value option.

Returns: int

A zero if the option is ValueNone, a one otherwise.

Example

 ValueNone |> ValueOption.count // evaluates to 0
 ValueSome 99 |> ValueOption.count // evaluates to 1

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

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

value : 'T

The specified default value.

voption : 'T voption

The input voption.

Returns: 'T

The voption if the voption is ValueSome, else the default value.

Example

 (99, ValueNone) ||> ValueOption.defaultValue // evaluates to 99
 (99, ValueSome 42) ||> ValueOption.defaultValue // evaluates to 42

Gets the value of the voption if the voption is ValueSome, otherwise evaluates defThunk and returns the result.

defThunk is not evaluated unless voption is ValueNone.

defThunk : unit -> 'T

A thunk that provides a default value when evaluated.

voption : 'T voption

The input voption.

Returns: 'T

The voption if the voption is ValueSome, else the result of evaluating defThunk.

Example

 ValueNone |> ValueOption.defaultWith (fun () -> 99) // evaluates to 99
 ValueSome 42 |> ValueOption.defaultWith (fun () -> 99) // evaluates to 42

exists p inp evaluates to match inp with ValueNone -> false | ValueSome x -> p x.

predicate : 'T -> bool

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

voption : 'T voption

The input value option.

Returns: bool

False if the option is ValueNone, otherwise it returns the result of applying the predicate to the option value.

Example

 ValueNone |> ValueOption.exists (fun x -> x >= 5) // evaluates to false
 ValueSome 42 |> ValueOption.exists (fun x -> x >= 5) // evaluates to true
 ValueSome 4 |> ValueOption.exists (fun x -> x >= 5) // evaluates to false

filter f inp evaluates to match inp with ValueNone -> ValueNone | ValueSome x -> if f x then ValueSome x else ValueNone.

predicate : 'T -> bool

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

voption : 'T voption

The input value option.

Returns: 'T voption

The input if the predicate evaluates to true; otherwise, ValueNone.

Example

 ValueNone |> ValueOption.filter (fun x -> x >= 5) // evaluates to ValueNone
 ValueSome 42 |> ValueOption.filter (fun x -> x >= 5) // evaluates to ValueSome 42
 ValueSome 4 |> ValueOption.filter (fun x -> x >= 5) // evaluates to ValueNone

flatten inp evaluates to match inp with ValueNone -> ValueNone | ValueSome x -> x

flatten is equivalent to bind id.

voption : 'T voption voption

The input value option.

Returns: 'T voption

The input value if the value is Some; otherwise, ValueNone.

Example

 (ValueNone: int ValueOption ValueOption) |> ValueOption.flatten // evaluates to ValueNone
 (ValueSome ((ValueNone: int ValueOption))) |> ValueOption.flatten // evaluates to ValueNone
 (ValueSome (ValueSome 42)) |> ValueOption.flatten // evaluates to ValueSome 42

fold f s inp evaluates to match inp with ValueNone -> s | ValueSome x -> f s x.

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

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

state : 'State

The initial state.

voption : 'T voption

The input value option.

Returns: 'State

The original state if the option is ValueNone, otherwise it returns the updated state with the folder and the voption value.

Example

 (0, ValueNone) ||> ValueOption.fold (fun accum x -> accum + x * 2) // evaluates to 0
 (0, ValueSome 1) ||> ValueOption.fold (fun accum x -> accum + x * 2) // evaluates to 2
 (10, ValueSome 1) ||> ValueOption.fold (fun accum x -> accum + x * 2) // evaluates to 12

fold f inp s evaluates to match inp with ValueNone -> s | ValueSome x -> f x s.

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

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

voption : 'T voption

The input value option.

state : 'State

The initial state.

Returns: 'State

The original state if the option is ValueNone, otherwise it returns the updated state with the folder and the voption value.

Example

 (ValueNone, 0) ||> ValueOption.foldBack (fun x accum -> accum + x * 2) // evaluates to 0
 (ValueSome 1, 0) ||> ValueOption.foldBack (fun x accum -> accum + x * 2) // evaluates to 2
 (ValueSome 1, 10) ||> ValueOption.foldBack (fun x accum -> accum + x * 2) // evaluates to 12

forall p inp evaluates to match inp with ValueNone -> true | ValueSome x -> p x.

predicate : 'T -> bool

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

voption : 'T voption

The input value option.

Returns: bool

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

Example

 ValueNone |> ValueOption.forall (fun x -> x >= 5) // evaluates to true
 ValueSome 42 |> ValueOption.forall (fun x -> x >= 5) // evaluates to true
 ValueSome 4 |> ValueOption.forall (fun x -> x >= 5) // evaluates to false

Gets the value associated with the option.

voption : 'T voption

The input value option.

Returns: 'T

The value within the option.

Example

 ValueSome 42 |> ValueOption.get // evaluates to 42
 (ValueNone: int ValueOption) |> ValueOption.get // throws exception!

Returns true if the value option is ValueNone.

voption : 'T voption

The input value option.

Returns: bool

True if the voption is ValueNone.

Example

 ValueNone |> ValueOption.isNone // evaluates to true
 ValueSome 42 |> ValueOption.isNone // evaluates to false

Returns true if the value option is not ValueNone.

voption : 'T voption

The input value option.

Returns: bool

True if the value option is not ValueNone.

Example

 ValueNone |> ValueOption.isSome // evaluates to false
 ValueSome 42 |> ValueOption.isSome // evaluates to true

iter f inp executes match inp with ValueNone -> () | ValueSome x -> f x.

action : 'T -> unit

A function to apply to the voption value.

voption : 'T voption

The input value option.

Example

 ValueNone |> ValueOption.iter (printfn "%s") // does nothing
 ValueSome "Hello world" |> ValueOption.iter (printfn "%s") // prints "Hello world"

map f inp evaluates to match inp with ValueNone -> ValueNone | ValueSome x -> ValueSome (f x).

mapping : 'T -> 'U

A function to apply to the voption value.

voption : 'T voption

The input value option.

Returns: 'U voption

A value option of the input value after applying the mapping function, or ValueNone if the input is ValueNone.

Example

 ValueNone |> ValueOption.map (fun x -> x * 2) // evaluates to ValueNone
 ValueSome 42 |> ValueOption.map (fun x -> x * 2) // evaluates to ValueSome 84

map f voption1 voption2 evaluates to match voption1, voption2 with ValueSome x, ValueSome y -> ValueSome (f x y) | _ -> ValueNone.

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

A function to apply to the voption values.

voption1 : 'T1 voption

The first value option.

voption2 : 'T2 voption

The second value option.

Returns: 'U voption

A value option of the input values after applying the mapping function, or ValueNone if either input is ValueNone.

Example

 (ValueNone, ValueNone) ||> ValueOption.map2 (fun x y -> x + y) // evaluates to ValueNone
 (ValueSome 5, ValueNone) ||> ValueOption.map2 (fun x y -> x + y) // evaluates to ValueNone
 (ValueNone, ValueSome 10) ||> ValueOption.map2 (fun x y -> x + y) // evaluates to ValueNone
 (ValueSome 5, ValueSome 10) ||> ValueOption.map2 (fun x y -> x + y) // evaluates to ValueSome 15

map f voption1 voption2 voption3 evaluates to match voption1, voption2, voption3 with ValueSome x, ValueSome y, ValueSome z -> ValueSome (f x y z) | _ -> ValueNone.

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

A function to apply to the value option values.

voption1 : 'T1 voption

The first value option.

voption2 : 'T2 voption

The second value option.

voption3 : 'T3 voption

The third value option.

Returns: 'U voption

A value option of the input values after applying the mapping function, or ValueNone if any input is ValueNone.

Example

 (ValueNone, ValueNone, ValueNone) |||> ValueOption.map3 (fun x y z -> x + y + z) // evaluates to ValueNone
 (ValueSome 100, ValueNone, ValueNone) |||> ValueOption.map3 (fun x y z -> x + y + z) // evaluates to ValueNone
 (ValueNone, ValueSome 100, ValueNone) |||> ValueOption.map3 (fun x y z -> x + y + z) // evaluates to ValueNone
 (ValueNone, ValueNone, ValueSome 100) |||> ValueOption.map3 (fun x y z -> x + y + z) // evaluates to ValueNone
 (ValueSome 5, ValueSome 100, ValueSome 10) |||> ValueOption.map3 (fun x y z -> x + y + z) // evaluates to ValueSome 115

Convert a Nullable value to a value option.

value : Nullable<'T>

The input nullable value.

Returns: 'T voption

The result value option.

Example

 System.Nullable<int>() |> ValueOption.ofNullable // evaluates to ValueNone
 System.Nullable(42) |> ValueOption.ofNullable // evaluates to ValueSome 42

Convert a potentially null value to a value option.

value : 'T

The input value.

Returns: 'T voption

The result value option.

Example

 (null: string) |> ValueOption.ofObj // evaluates to ValueNone
 "not a null string" |> ValueOption.ofObj // evaluates to (ValueSome "not a null string")

Returns voption if it is Some, otherwise returns ifNone.

ifNone : 'T voption

The value to use if voption is None.

voption : 'T voption

The input option.

Returns: 'T voption

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

Example

 ((ValueNone: int ValueOption), ValueNone) ||> ValueOption.orElse // evaluates to ValueNone
 (ValueSome 99, ValueNone) ||> ValueOption.orElse // evaluates to ValueSome 99
 (ValueNone, ValueSome 42) ||> ValueOption.orElse // evaluates to ValueSome 42
 (ValueSome 99, ValueSome 42) ||> ValueOption.orElse // evaluates to ValueSome 42

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

ifNoneThunk is not evaluated unless voption is ValueNone.

ifNoneThunk : unit -> 'T voption

A thunk that provides an alternate value option when evaluated.

voption : 'T voption

The input value option.

Returns: 'T voption

The voption if the voption is ValueSome, else the result of evaluating ifNoneThunk.

Example

 (ValueNone: int ValueOption) |> ValueOption.orElseWith (fun () -> ValueNone) // evaluates to ValueNone
 ValueNone |> ValueOption.orElseWith (fun () -> (ValueSome 99)) // evaluates to ValueSome 99
 ValueSome 42 |> ValueOption.orElseWith (fun () -> ValueNone) // evaluates to ValueSome 42
 ValueSome 42 |> ValueOption.orElseWith (fun () -> (ValueSome 99)) // evaluates to ValueSome 42

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

voption : 'T voption

The input value option.

Returns: 'T[]

The result array.

Example

 (ValueNone: int ValueOption) |> ValueOption.toArray // evaluates to [||]
 ValueSome 42 |> ValueOption.toArray // evaluates to [|42|]

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

voption : 'T voption

The input value option.

Returns: 'T list

The result list.

Example

 (ValueNone: int ValueOption) |> ValueOption.toList // evaluates to []
 ValueSome 42 |> ValueOption.toList // evaluates to [42]

Convert the value option to a Nullable value.

voption : 'T voption

The input value option.

Returns: Nullable<'T>

The result value.

Example

 (ValueNone: int ValueOption) |> ValueOption.toNullable // evaluates to new System.Nullable<int>()
 ValueSome 42 |> ValueOption.toNullable // evaluates to new System.Nullable(42)

Convert an option to a potentially null value.

value : 'T voption

The input value.

Returns: 'T

The result value, which is null if the input was ValueNone.

Example

 (ValueNone: string ValueOption) |> ValueOption.toObj // evaluates to null
 ValueSome "not a null string" |> ValueOption.toObj // evaluates to "not a null string"