Implement new Concept Exercise: higher-order-functions

[ErikSchierboom]

This issue describes how to implement the higher-order-functions 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 more advanced aspects of the Concept of Higher-order Functions in F#.

Learning objectives

• Know how to define and read function types.
• Know how to return functions.
• Know how to pass functions as arguments.
• Know how to define lambda functions.
• Know of some built-in higher-order functions (e.g. List.exists).

Out of scope

• Recursion.
• Mutually recursive functions.
• Custom operators.
• Monadic functions.
• Function composition.

Concepts

The Concepts this exercise unlocks are:

• higher-order-functions: know how to return functions; know how to pass functions as arguments; know how to define lambda functions; know of some built-in higher-order functions .

Prerequisites

This exercise's prerequisites Concepts are:

• lists: know how to work with lists, which has many built-in higher-order functions we can use.

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

Resources to refer to

Hints

• Functions: introduction to functions in F#.
• Lambda expressions: how to define a lambda expression.
• Function values: discusses function types and passing functions as values.

After

• Functions: introduction to functions in F#.
• Lambda expressions: how to define a lambda expression.
• Function values: discusses function types and passing functions as values.
• First-class functions: overview of first-class function features of F#.
• Defining functions: more in-depth discussion on how to define functions.

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.

[ErikSchierboom]

I'm working on this.