The random album cover project

I find that having a hands-on project is very helpful for me when I’m trying to learn to things in programming, and I’ve needed a fairly simple project to help me learn Scala for some time now.  Some of my earliest ideas for toy projects were a little too ambitious.

I was trying at one time to write a small Android app in Scala, but Android itself is a fairly complex new system that I was also learning simultaneously, and having poked around at it for a bit I’ve decided that it will probably be best to learn Android in its native Java before spilling chocolatey Scala into its rich peanut butter APIs (in addition to that, I don’t relish the prospect of adding a ProGuard step to my compilation cycle).

My second idea was to produce a framework for solving some classic sets of computer sciencey problems, to wit the 99 Prolog Problems and possibly (though my math skills are sadly lacking) the Project Euler problems.  This is still something I’m interested in doing (for my own reference, the Python wiki also has some promising problem sets).  I quickly ran into some trouble with this, as well.  It might be possible to come up with a set of specs / ScalaTest / etc tests which could then just be run as a suite, with the user filling in the implementations for particular problems, but I came to realize that what I really wanted was a sort of unit-test like framework that would detect test implementations and automatically run them over given sets of verified input and output data.

This is a worthwhile goal, and I still would like to do it (FWIW, I’ve also dabbled in writing such a framework for clojure, though it’s been collecting a bit of dust recently).  The problem is that it’s a fairly advanced problem; doing it the way I envision it involves a level of metaprogramming and reflection that isn’t really suited for a first project.  Compounding that, in Scala figuring out the proper type definitions of the individual tests might well be an interesting part of finding solutions to the exercises; if I define it myself in unit test definitions the problem sets may well lose a bit of their didactic panache.

While I was ruminating about these matters I chanced upon a sort of low-level internet meme which had never quite broken through to the big leagues: the random album cover algorithm (here’s a partial history).  Basically, you combine a random wikipedia page, a random quotation, and a random flickr image  to produce a random album cover.  The original flickr pool seems to be dead now, but examples abound.

As a meme, this frankly does not appear to have the legs of, say, Nyan Cat or Rick Astley.  As a project for learning Scala, though, it’s well-nigh perfect:

  • It can be structured as a classic three-tiered web application.
  • It involves using publicly available HTTP APIs, plus some HTML scraping and file downloading.
  • The project is simple and small enough that it should be easy to quickly try out different back-end stores as well as different web frameworks and toolkits; this will hopefully also get me to learn the Cake Pattern and other DI equivalents.
  • The application itself is easy to scale up in complexity, with the first version just getting the three data items, the second combining them to generate a boilerplate cover, and then adding UI and image processing to allow the user to style the result somewhat.
  • The image processing bit could involve Scala / Java interoperability (assuming there are more Java image-processing libraries than Scala ones, which frankly I have no idea about).
  • Eventually the thing could get ported and deployed to a GAE-like cloud environment.
  • It could potentially be ported over to an Android app as well.

So.  Here is the github repository.  What I have got so far is a very basic Scalatra web application which keeps an in-memory album cover list.  It doesn’t currently actually do any HTTP calls right now, about which more later, but it’s a decent starting point, and I feel that I’m well on my way to actually doing something somewhat fun in Scala.

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