Implement new Concept Exercise: error-handling

Read docs/concept-exercises.md, docs/rationale-for-v3.md, docs/features-of-v3.md, and languages/fsharp/reference/implementing-a-concept-exercise.md first. Use languages/fsharp/exercises/concept/numbers/.meta/design.md and .meta/config.json as references, then follow the implementation instructions. Done means the error-handling exercise is implemented for the stated learning objectives and requires no representer or analyzer changes.

This issue describes how to implement the error-handling concept exercise for the F# track.

Getting started

Please please please read the docs before starting. Posting PRs without reading these docs will be a lot more frustrating for you during the review cycle, and exhaust Exercism's maintainers' time. So, before diving into the implementation, please read up on the following documents:

• The features of v3.
• Rationale for v3.
• What are concept exercise and how they are structured?

Please also watch the following video:

• The Anatomy of a Concept Exercise.

Goal

The goal of this exercise is to teach the student the basics of the Concept of Error Handling in F#.

Learning objectives

• Know when to use exceptions vs results vs options.
• Know what railway oriented programming is.
• Know how to use railway oriented programming, including custom operators.

Out of scope

• Custom computation expression to deal with error-handling.
• Custom operators to deal with error-handling applicatively (like <*>).
• Converting error-handling to and from other types (like arrays of lists).

Concepts

The Concepts this exercise unlocks are:

• error-handling: know when to use exceptions vs results vs options; know what railway oriented programming is; know how to use railway oriented programming, including custom operators.

Prerequisites

This exercise's prerequisites Concepts are:

• options: know how to work with option values.
• results: know how to work with result values.
• exceptions: know how to work with exceptions.
• operator-overloading: how to define custom operators.

Any data types used in this exercise (e.g. strings) should also be added as prerequisites.

Resources to refer to

Hints

• Railway oriented programming: shows what railway oriented programming is and how to use it in F#.

After

• Railway oriented programming: shows what railway oriented programming is and how to use it in F#.
• Exceptions vs error-handling: when to use exceptions vs error-handling.

Representer

This exercise does not require any specific representation logic to be added to the representer.

Analyzer

This exercise does not require any specific logic to be added to the analyzer.

Implementing

To implement this exercise, please follow these instructions.

Help

If you have any questions while implementing the exercise, please post the questions as comments in this issue.