oliverm / imgedit

Technical test for OnTheMarket

imgedit

An implementation of the OnTheMarket code test, by Oliver Mooney

Installation

The project is implemented in Clojure, using Leiningen.

If neither is installed on your machine, install:

1. A current JVM (via https://java.com/en/download/ or using a commandline package manager).
2. Leiningen (via the instructions at https://leiningen.org)

Once both are installed, clone the project at the command line with

git clone https://github.com/OliverM/imgedit.git

This will install the source into the imgedit directory.

Usage

In the project directory, type lein run at the command line to launch the interface.

Similarly, to run tests, in the project directory type lein test.

Implementation discussion

I implemented the front-end parser using Instaparse. I hadn't used Instaparse previously and wanted to gain some experience using it. On the whole it went smoothly but there is an overlap between its post-parsing functionality and spec's conform functionality, so in general I didn't use the latter as widely as I might otherwise.

The requirements are implemented in a layered fashion; the parser limits numeric dimensions to positive integers beginning with 1, while the specs for dimension values limit them to 1-250, the image-command spec ensures commands fall within image boundaries, and the fdef generators for the inner implementation commands ensure commands are generated images with compatible boundaries.

Assumptions & Ambiguities

• The spec stipulates arguments are separated by a single space; for ease of use I've relaxed this to one or more spaces
• The spec says nothing about communication of parsing errors, so I've stuck to Instaparse's default for this, and leveraged it further by insisting numbers begin with 1 at the parsing level, rather than accepting numbers like "04"
• The spec doesn't constrain the set of colours beyond single characters, so I'm just using char? as a validation of the parsed value
• The spec says nothing about the starting state of the program, so I'm initialising it to a default state of a blank 10 x 10 image