[v3] Implement new Concept Exercise: variadic-functions

Start by reading docs/concept-exercises.md, docs/rationale-for-v3.md, and docs/features-of-v3.md, then review the linked Anatomy of a Concept Exercise video. Create the variadic-functions structure under languages/clojure/exercises/concept, including the .docs files, .meta/design.md, .meta/Example.clj, the exercise source, and its test; done means it teaches the listed objectives without representer or analyzer changes.

This issue describes how to implement the variadic-functions concept exercise for the Clojure 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 how to use variadic functions in Clojure.

Learning objectives

The student will learn:

• That functions may also define a variable number of parameters
• Usage of &
• Examples in clojure.core such as str and format

Out of scope

• Multi-arity functions
• Creating named parameters through destructuring args

Concepts

• default-arguments
• evaluation
• functions
• rest-parameters

Prerequisites

• basic-functions

Resources to refer to

Hints

• Clojure Guide: Functions

After

• clojure-doc.org - Functions in Clojure

Representer

This exercise does not require any modifications to the track's representer.

Analyzer

This exercise does not require any modifications to the track's analyzer.

Implementing

To implement a concept exercise, the following files must be created:

languages
└── clojure
    └── exercises
        └── concept
            └── <SLUG>
                ├── .docs
                |   ├── instructions.md
                |   ├── introduction.md
                |   ├── hints.md
                |   └── after.md (optional)
                ├── .meta
                |   |── design.md
                |   └── Example.clj
                ├── <NAME>.clj
                └── <NAME>_test.clj

Help

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