Implement Option type

[NickSeagull]

Reasoning

The Option type is a staple in functional programming languages and has found its way into more mainstream languages as well, such as Swift's Optional and Kotlin's Optional. It is used to represent a value that can either be present (Some) or absent (None). The Option type is commonly used for:

1. Null Safety: One of the primary uses is to safely encapsulate the absence of a value, as opposed to using null or nil, which can lead to runtime errors.

2. Function Return Types: It's often used as the return type of functions that may or may not produce a value. For example, a function that searches for an element in a collection can return an Option to signify whether the search was successful.

3. Configuration: It's useful for optional configuration settings that have sensible defaults.

4. Pipeline Processing: Higher-order functions like map, filter, and flatMap can be defined on an Option, making it composable in data pipelines.

5. Error Handling: While Option is not a substitute for proper error types like Either or Result, it can be used for simple error handling scenarios where the only important information is the presence or absence of a value.

Incorporating these considerations, let's define the API for the Option type.

Functions for the Option Module

Constructors

• some: Create an Option with a value (Some)
• none: Create an empty Option (None)
• fromNullable: Create an Option from a value that could be null

Basic Queries

• isEmpty: Check if the Option is None
• isSome: Check if the Option is Some
• getOrElse: Retrieve the value or a default if the Option is None

Transformations

• map: Apply a function to the inner value of the Option if it's Some
• flatMap: Apply a function that returns an Option to the inner value of the Option if it's Some

Filtering

• filter: Apply a predicate function to the Option and turn it into None if the predicate fails

Side Effects

• forEach: Execute a side-effect function if the Option is Some

Error Handling

• orElse: Chain multiple Options together, returning the first Some found
• getOrElseThrow: Retrieve the value or throw an exception if the Option is None

Conversions

• toList: Convert the Option to a list containing zero or one element
• toString: Convert the Option to its string representation

By adopting a rich and expressive set of operations, the Option type can serve as a powerful tool for safe and expressive programming in NeoHaskell. As always, the API can be expanded or refined based on user feedback and real-world use cases.

[NickSeagull]

Fixed in v0.1.0 - we implemented it as a Maybe reexport