Caffeinated Simpleton

After yesterday’s introduction to the syntax of clojure, now I’m going to start organizing my code a bit more and pulling in real data.

Templating

The first thing I want to do is abstract out a base page so that I don’t need to worry about headers, JS libraries, standard CSS, and all that when going from page to page. To do this, I’ll create a “page” function in a new namespace.

Then I add this into our original page.

Now I can call the “page” function, pass it a title and some contents, and it outputs a full page. Perhaps later on we’ll make it so we can derive templates from other templates, but I have no need for that yet.

Getting My Twitter Feed

Let’s make it so that getting “/justin_tulloss” will give me my twitter feed. To do that, I add a handler to our servlet.

Now when I go to http://localhost:8080/justin_tulloss, it will say “Welcome justin_tulloss”. Pretty high tech stuff.

Now let’s see if I can change that justin_tulloss parameter into my actual twitter data. First, I head over to the twitter API docs. The public timeline doesn’t require any authentication, so let’s pull that down first. The public timeline is a list of “status” messages, which we will map to html representations of the same. To do this, I used the clj-http-client library by Mark McGranaghan. It was a pain to get installed because I don’t understand Java JAR files fully, but once I got it figured out, it worked great.

Hopefully this code isn’t hard to follow, but let’s take a look. The “Welcome” part is the same. Then we map everything that we read from the twitter URL into a twitter-status function, which just grabs some data out of the statuses and displays it.

Referring back to the non-templating code, the “read-json-string” function is in clojure.contrib.json.read, which you can get here. The *twitter-url* is a global constant. Apparently it’s a lisp thing to surround globals with asterisks. I wonder if that also applies to global constants.

Well, that’s all for tonight. Next time we’ll fetch some more relevant data from twitter and see what we can do with it. As always, the complete code is on github.

I’ve decided I want to learn clojure. Clojure is a lisp dialect that runs on the Java Virtual Machine. It’s all the rage these days, and I want to be cool. I’m going to post my trials and tribulations here for others to read and hopefully learn from. If you are a better hacker than I and see problems with what I’ve posted, please comment! This is going to be a multi-day process, and a slow one as I don’t have much time, but I hope to finish a project within the next six months.

There are a couple problems with Clojure and I. First of all, I’ve never programmed in any lisp dialect. Second of all, I’ve never programmed in Java. Clearly I do not have the tools to get into this, but I’m going to go for it anyway.

The Project

I’ve been thinking a lot about Twitter recently, and there are some really cool applications of Twitter that I find kind of exciting. However, Twitter’s signal to noise ratio can quickly become unbearable. So, I thought I’d come up with a Twitter feed app that will organize people you care about, conversations you want to monitor, tweets around where you are, and the regular twitter feed into a sort of Twitter portal. It should be fun and easy, and it’s not the project that’s important. It’s learning Clojure. I’m going to call it Flockr for maximum Web 2.0 street cred. You can find the source on github.

Getting Started

I’m using Compojure as my web framework. I like web frameworks, especially for little projects like this that don’t need any specialized plumbing. Compojure isn’t terribly mature, but it should be good enough to get me off the ground.

Installing compojure is easy. Just download, compile with ant, and put the resulting jar file in your classpath. Being a vim guy, I wanted clojure syntax highlighting and auto-indenting. There’s a vim package available to do that stuff, and I recommend it.

The First Page

This is basically copied straight off the compojure “Getting Started” page. However, this is the first time I’ve really looked at lisp, so let’s see what this does.

Clojure Basics (or at least, what I’ve inferred about Clojure thus far)

Parentheses indicate a list. I’m a big C/Python/JavaScript guy, so this a bit strange, but I can deal. Evaluation is simply evaluating every list that is passed into the REPL. This first program has three things that are evaluated. The first is the namespace. The second is the servlet, and the third is the server. Let’s that a closer look at the first line.

Returns the result of the “ns” function, which creates a new namespace called “index” (in this case). Within this namespace, we are dependent on the “compojure” namespace. We pass the “:use” key to indicate this.

The colon syntax is something I’m still getting used to. It means a key, which makes sense in a map, but it would appear that you can also put keys in other data structures.

The only other things you need to know to understand the rest of the code is “[]” and “{}”. “[]” is a vector. I’m not certain I understand when to use vectors versus lists except for performance. “{}” is a map. A colon indicates a key (IE :port), the thing following it is the value (IE 8080). Commas are optional, and don’t seem to be used in examples at all.

Doing something real

Ok, so we’ve got something up and running. That’s good. Now let’s grab some twitter statuses. Unfortuneatly, it’s past 4 in the morning. This will have to wait for another day.