Modules · Data · Collection · Optional

Collection.Optional

An optional value — either present, carrying a value, or absent. Because it is a real generic union rather than a nullable flag, it nests cleanly and must be checked before its value can be used. Construct one with Collection.Optional.present or Collection.Optional.absent.

Types

Collection.Optional

Functions

Types

Collection.Optional

A value that is either present, carrying a value, or absent. Because it is a real generic union rather than a nullable flag, it nests cleanly: a Collection.Optional(Collection.Optional(Text)) can tell absent apart from present-but-empty. Construct one with Collection.Optional.present or Collection.Optional.absent.

Generics

Name	Description
`ValueType`	The type of value the optional may hold.

Options

Option	Type	Description
`present`	`ValueType`	The present case; carries a value.
`absent`	—	The absent case; carries nothing.

Definition

TYPE Collection.Optional(ValueType)
  OPTION ValueType present
  OPTION absent

A Collection.Optional(ValueType) is either present with a value or absent.

Example

LET Collection.Optional(Text) name = Collection.Optional.present "Ada"

Constructs a present optional holding "Ada"; Collection.Optional.absent makes the empty case.

Functions

Collection.Optional.Default

The contained value, or a fallback when the optional is absent.

Generics

Name	Description
`ValueType`	The type of value the optional may hold.

Parameters

Name	Type	Description
`optionalValue`	`Collection.Optional(ValueType)`	The optional to read.
`defaultValue`	`ValueType`	Returned when the optional is absent.

Returns

Returns ValueType — the contained value when present, otherwise defaultValue.

Example

LET Text shown = Collection.Optional.Default maybeName "guest"

Unwraps the optional, falling back to "guest" when it is absent.

Collection.Optional.If

Runs a callback with the contained value when an optional is present, and does nothing when it is absent.

Generics

Name	Description
`ValueType`	The type of value the optional may hold.

Parameters

Name	Type	Description
`optionalValue`	`Collection.Optional(ValueType)`	The optional to test.

Holes

Name Returns Description

callback

nothing

Run once with the unwrapped value when the optional is present; never run when it is absent.

Inputs

Name	Type	Description
`value`	`ValueType`	The value the optional holds, unwrapped.

Example

LET Collection.Optional(Text) maybeName = Collection.Optional.present "Ada"

// Run the callback only when the optional is present
Collection.Optional.If maybeName
  INPUT Text name
  Ui.Content.Text name

Constructs an optional holding "Ada"; Collection.Optional.If then runs the callback with the unwrapped value bound to name. When the optional is absent, the callback never runs.

Collection.Optional.IfNot

Runs a callback when an optional is absent, and does nothing when it is present.

Generics

Name	Description
`ValueType`	The type of value the optional may hold.

Parameters

Name	Type	Description
`optionalValue`	`Collection.Optional(ValueType)`	The optional to test.

Holes

Name	Returns	Description
`callback`	`nothing`	Run once when the optional is absent; never run when it is present. It receives no inputs.

Example

Collection.Optional.IfNot maybeName
  Ui.Content.Text "No name yet"

Shows the placeholder text only while maybeName is absent.

Collection.Optional.IsAbsent

Yields yes when the optional carries no value.

Generics

Name	Description
`ValueType`	The type of value the optional may hold.

Parameters

Name	Type	Description
`optionalValue`	`Collection.Optional(ValueType)`	The optional to test.

Returns

Returns Logic.Maybe — yes when absent, otherwise no — the negation of IsPresent.

Example

LET Logic.Maybe missing = Collection.Optional.IsAbsent maybeName

The opposite of IsPresent.

Collection.Optional.IsPresent

Yields yes when the optional carries a value.

Generics

Name	Description
`ValueType`	The type of value the optional may hold.

Parameters

Name	Type	Description
`optionalValue`	`Collection.Optional(ValueType)`	The optional to test.

Returns

Returns Logic.Maybe — yes when present, otherwise no.

Example

LET Logic.Maybe hasName = Collection.Optional.IsPresent maybeName

A reactive test you can feed to Logic.If and friends.

Collection.Optional.Map

A new optional holding the result of a block, or absent when the input is absent.

Generics

Name	Description
`OptionalType`	The value type of the input optional.
`ResultType`	The type the block produces, and the value type of the result.

Parameters

Name	Type	Description
`optionalValue`	`Collection.Optional(OptionalType)`	The optional to transform.

Holes

Name Returns Description

mapFn

ResultType

Run only when the optional is present, with its unwrapped value; its result becomes the new present value.

Inputs

Name	Type	Description
`value`	`OptionalType`	The unwrapped value, when present.

Returns

Returns Collection.Optional(ResultType) — present with the mapped result, or absent when the input was absent.

Example

LET Collection.Optional(Maths.Integer) length = Collection.Optional.Map maybeName
  INPUT Text name
  Text.Length name

Maps the value through when present, staying absent otherwise — no unwrapping needed.

Collection.Optional.Or

The first optional if present, otherwise the second.

Generics

Name	Description
`ValueType`	The type of value the optionals may hold.

Parameters

Name	Type	Description
`optionalA`	`Collection.Optional(ValueType)`	The preferred optional.
`optionalB`	`Collection.Optional(ValueType)`	The fallback optional.

Returns

Returns Collection.Optional(ValueType) — optionalA when present, otherwise optionalB.

Example

LET Collection.Optional(Text) chosen = Collection.Optional.Or fromUser fromDefaults

Prefers the user's value, falling through to defaults; the result is still an optional.

Collection.Optional.Select

Picks one of two values by whether the optional is present.

Generics

Name	Description
`ValueType`	The type of value the optional may hold.
`ResultType`	The type of the two values chosen between, and of the result.

Parameters

Name	Type	Description
`optionalValue`	`Collection.Optional(ValueType)`	The optional to test.
`presentValue`	`ResultType`	Returned when the optional is present.
`absentValue`	`ResultType`	Returned when the optional is absent.

Returns

Returns ResultType — presentValue or absentValue, matching the optional.

Example

LET Text status = Collection.Optional.Select maybeName "signed in" "signed out"

Chooses purely on presence; unlike Default, the two results need not be the value's own type.

Collection.Optional.ToArray

The optional as an array: one element when present, empty when absent.

Generics

Name	Description
`ValueType`	The type of value the optional may hold.

Parameters

Name	Type	Description
`optionalValue`	`Collection.Optional(ValueType)`	The optional to convert.

Returns

Returns Collection.Array(ValueType) — a one-element array when present, an empty array when absent.

Example

LET Collection.Array(Text) names = Collection.Optional.ToArray maybeName

Bridges an optional into array operations like Each and Map.

Collection.Optional.Zero

An absent optional of the value type.

Generics

Name	Description
`ValueType`	The value type of the optional.

Returns

Returns Collection.Optional(ValueType) — an absent optional.

Example

STATE Collection.Optional(Text) maybeName = Collection.Optional.Zero

The empty starting point — the same as Collection.Optional.absent.

Collection.Optional

Contents

Types

Functions

Types

Collection.Optional

Generics

Options

Definition

Example

Functions

Collection.Optional.Default

Generics

Parameters

Returns

Example

Collection.Optional.If

Generics

Parameters

Holes

Inputs

Example

Collection.Optional.IfNot

Generics

Parameters

Holes

Example

Collection.Optional.IsAbsent

Generics

Parameters

Returns

Example

Collection.Optional.IsPresent

Generics

Parameters

Returns

Example

Collection.Optional.Map

Generics

Parameters

Holes

Inputs

Returns

Example

Collection.Optional.Or

Generics

Parameters

Returns

Example

Collection.Optional.Select

Generics

Parameters

Returns

Example

Collection.Optional.ToArray

Generics

Parameters

Returns

Example

Collection.Optional.Zero

Generics

Returns

Example