transitive-closure

Coding assessment (Scala 3, Cats, ScalaTest).

Completed in 2019, and currently maintained as a demonstration project.

Pre-requisites

• sbt

Usage

• sbt test - test
• sbt styleFix - fix formatting and linting errors
• sbt styleCheck - check for formatting and linting errors
• sbt dev - allow compiler warnings to not fail the compilation

Objective

A database contains Foo items, and all their references do exist in db. One can use FooRepository interface to interact with db.

The task is to implement a readClosure function, which accepts a list of FooId and returns them and all objects which they refer to (directly or indirectly). The function should be tested with mock implementations of FooRepository (which should also be developed).

Technical decisions

1. Tail recursive monadic function is used

This allows large relation graphs

2. Cyclic relations are allowed

Items can refer to each other in any order

3. Each item will be requested exactly once

This was not required by the objective. However, since all elements are merged in a single Set, there will ever be no need in fetching some element twice, that's why this restriction was added (and tested). Also this makes sense in case of ring-like relations.