Caffeinated Simpleton

After the first two posts in this series, we have a site that displays the twitter public timeline and twitter searches. Now let’s customize this by allowing users to access their own twitter accounts.

To do that, we need to allow users to log in to their twitter accounts. Twitter hasn’t rolled out their OAuth solution yet, so we’ll have to ask users to trust us with their twitter names and passwords. For now, we won’t store the password, so all we need to do is get it out of a form and store it in a session.

Processing Forms in Compojure

This is pretty easy. Compojure provides a “params” hash-map that has the parameters of the servlet, which we will pass to a “login” controller. There are several things provided to the servlet. I won’t bore you with details of creating the form itself, so here’s the server side code that processes “twitter-user” and “twitter-password”.

As you can see, we have some new syntactic goodies to learn about. “session” is a map provided by Compojure. It is thread safe, which in clojure, is done through transactional memory. Dealing with that transaction is what most of this code does. dosync is a macro that allows many expressions to be executed in one transaction. alter takes a reference (session), a function that will alter the reference (assoc) and the arguments for the altering function. We finish our dosync call, which executes the transaction, and our session is all set.

After we set up our session, we redirect to the url of the user. We pull the user name out of the session. The “@” symbol is a macro that refers to the deref function, which allows us to get values out of references. If no name was provided, we kick back to the home page.

Pretty clean and painless. Clojure isn’t so bad.

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.