Option

Utilities for working with the Option data type.

The Option type is an enum that represents the possibility of something being present (with the Some variant), or not (with the None variant). There’s no standalone null or nil type in Grain; use an Option where you would normally reach for null or nil.

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from "option" include Option

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let hasValue = Some(1234) // Creates an Option containing 1234

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let noValue = None // Creates an Option containing nothing

Values

Functions and constants included in the Option module.

Option.isSome

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isSome : (option: Option<a>) => Bool

Checks if the Option is the Some variant.

Parameters:

Returns:

Option.isNone

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isNone : (option: Option<a>) => Bool

Checks if the Option is the None variant.

Parameters:

Returns:

Option.contains

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contains : (value: a, option: Option<a>) => Bool

Checks if the Option is the Some variant and contains the given value. Uses the generic == equality operator.

Parameters:

Returns:

Option.expect

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expect : (msg: String, option: Option<a>) => a

Extracts the value inside a Some option, otherwise throws an exception containing the message provided.

Parameters:

Returns:

Throws:

Failure(String)

• When the option is None

Option.unwrap

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unwrap : (option: Option<a>) => a

Extracts the value inside a Some option, otherwise throws an exception containing a default message.

Parameters:

Returns:

Throws:

Failure(String)

• When the option is None

Option.unwrapWithDefault

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unwrapWithDefault : (default: a, option: Option<a>) => a

Extracts the value inside a Some option or provide the default value if None.

Parameters:

Returns:

Option.map

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map : (fn: (a => b), option: Option<a>) => Option<b>

If the Option is Some(value), applies the given function to the value and wraps the new value in a Some variant.

Parameters:

Returns:

Option.mapWithDefault

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mapWithDefault : (fn: (a => b), default: b, option: Option<a>) => b

If the Option is Some(value), applies the given function to the value to produce a new value, otherwise uses the default value. Useful for unwrapping an Option while providing a fallback for any None variants.

Parameters:

Returns:

Option.mapWithDefaultFn

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mapWithDefaultFn :
  (fn: (a => b), defaultFn: (() => b), option: Option<a>) => b

If the Option is Some(value), applies the fn function to the value to produce a new value. If the Option is None, calls the defaultFn function to produce a new value. Useful for unwrapping an Option into a value, whether it is Some or None.

Parameters:

Returns:

Option.flatMap

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flatMap : (fn: (a => Option<b>), option: Option<a>) => Option<b>

If the Option is Some(value), applies the given function to the value to produce a new Option.

Parameters:

Returns:

Option.filter

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filter : (fn: (a => Bool), option: Option<a>) => Option<a>

Converts Some(value) variants to None variants where the predicate function returns false. if the fn return true returns Some(value), otherwise returns None.

Parameters:

Returns:

Option.zip

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zip : (optionA: Option<a>, optionB: Option<b>) => Option<(a, b)>

Combine two Options into a single Option containing a tuple of their values.

Parameters:

Returns:

Option.zipWith

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zipWith :
  (fn: ((a, b) => c), optionA: Option<a>, optionB: Option<b>) => Option<c>

Combine two Options into a single Option. The new value is produced by applying the given function to both values.

Parameters:

Returns:

Option.flatten

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flatten : (option: Option<Option<a>>) => Option<a>

Flattens nested Options.

Parameters:

Returns:

Examples:

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Option.flatten(Some(Some(1))) == Some(1)

Option.toList

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toList : (option: Option<a>) => List<a>

Converts an Option to a list with either zero or one item.

Parameters:

Returns:

Option.toArray

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toArray : (option: Option<a>) => Array<a>

Converts an Option to an array with either zero or one item.

Parameters:

Returns:

Option.toResult

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toResult : (err: a, option: Option<b>) => Result<b, a>

Converts the Option to a Result, using the provided error in case of the None variant.

Parameters:

Returns:

Option.sideEffect

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sideEffect : (fn: (a => Void), option: Option<a>) => Void

If the Option is Some(value), applies the fn function to the value without producing a new value.

Parameters:

Option.peek

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peek : (fn: (a => Void), option: Option<a>) => Option<a>

If the Option is Some(value), applies the fn function to the value without producing a new value. Useful for inspecting Options without changing anything.

Parameters:

Returns:

Option.(||)

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(||) : (optionA: Option<a>, optionB: Option<a>) => Option<a>

Behaves like a logical OR (||) where the first Option is only returned if it is the Some variant and falling back to the second Option in all other cases.

Parameters:

Returns:

Option.(&&)

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(&&) : (optionA: Option<a>, optionB: Option<a>) => Option<a>

Behaves like a logical AND (&&) where the first Option is only returned if it is the None variant and falling back to the second Option Result in all other cases.

Parameters:

Returns: