[v3] Implement new Concept Exercise: `Reduce`

Read docs/features-of-v3.md, docs/rationale-for-v3.md, and docs/concept-exercises.md, then watch the linked Anatomy of a Concept Exercise video. Create the listed files under languages/clojure/exercises/concept/, including the documentation, design, example, source, and test files. Done means the exercise teaches reducing a function on a collection without covering transducers and follows the specified prerequisites and concept.

This issue describes how to implement the Reduce 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 the reduce function is implemented in Clojure.

Learning objectives

The student will gain a general understanding of:

• The concept of reducing a function on a collection

Out of scope

• Transducers

Concepts

• higher-order-functions

Prerequisites

• basics

Resources to refer to

Clojure for the Brave and True - Core Functions in Depth

Representer

The Clojure Representer is currently being implemented and contributions are welcome.

Analyzer

The Clojure Analyzer is currently being implemented and contributions are welcome.

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.