Thursday, July 21, 2011

Learning clojure just in time

It looks like we've moved to clojure at just the right moment.

As mentioned, I started using emacs for the first time again in ages. While I still struggle remembering all the useful key combos I did get a little bit of help in the transition by installing aquamacs. It keeps buffers in tabs and lets you use cmd-c,x,v while you're trying to remember how to work the yank buffer.

I'm really liking clojure so far. I'm finally writing tests again (not sure I actually ever did for any of the other languages) and it's nice to have that inside emacs and also have the REPL to try things out.

So, Day 1 only had two excercises. I'm going to just point to aimee's entry on that, because we both came up with pretty similar code.

But let's look at the second exercise
Write a function called (collection-type col) that returns :list, :map, or :vector based on the type of collection col.
I got the following:

I wasn't quite happy with repeating the col argument for each condition. So I started to play around with using the various test methods (list? vector? map?) as keys in a map and then filtering the keys based on the collection argument given. I eventually gave up on it, because it is a rather silly approach. But it was an interesting opportunity to play around with the language.

Then I noticed multi-methods and became interested. Method dispatch based on the result of a function applied to the arguments of the method. This is pretty powerful and will probably take a while to get comfortable with. I used the rather simplistic approach of dispatching on the class to do the second exercise again.

This is silly, too. And it works pretty sloppily. The empty list creates an instance of PersistentList$EmptyList which doesn't seem to match PersistenList. But whatever, it's good enough and it got me thinking about multi-methods. There is more on those in this blog post.

And now it's on to day 2, where apparently we see the list comprehensions I was so impressed with in Erlang enter clojure, too.