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Happy 2nd Birthday Clojure

Clojure is two years old and it's looking good. Clojure development has been a bit quiet lately but that's because lots of big changes are apparently being worked on behind the scenes, for example rewriting Clojure in Clojure (and enhancing the Java-Clojure interop along the way, to help make this more possible). Meanwhile clojure-contrib continues to grow and the community continues to be vibrant.

I've been putting Clojure to good use at work in data munging and reporting. I've got data in an MS SQL Server database on one box (not by choice, I assure you) and a mysql database on another box, and then there's a bunch of data files in wide variety of other formats floating around the network. I use Clojure to query and compare it all.

Thanks to JDBC and clojure.contrib.sql it's easy to slurp data from a DB into a bunch of Clojure hash-maps. Thanks to clojure.contrib.duck-streams and Clojure's good regex support, the same is true of data files in general.

In the past I'd have written some enormous SQL queries to generate reports, but it's so much easier to use Clojure's wide array of sequence-manipulation functions to manipulate hash-maps. Doing what I want is rarely more difficult than mapping some transformation over the data, filtering out the data I want, and then formatting it nicely (which is easy thanks to Common Lisp-style formatting).

And once I notice patterns in how I'm using those things, I write a few functions and macros to make it more concise. Consicion is one area where Lisps cannot be beaten (short of APL). For example, give me all data from the mysql db "data4" which is collected at "Site1" and happened before 2008, and group it by the person who collected it:

user> (group-by :collector 
                (filter #(and (= (:site %) "Site1")
                              (date-before? (:date %) 
                                            (date-from-string "2008-01-01")))
                        (mysql-data :data4)))

date-from-string isn't a standard function but here's how easy it is to write it, thanks to the JVM:

(defn date-from-string [s]
  (.parse (java.text.SimpleDateFormat. "yyyy-mm-DD") s))

That's pretty much how my data-querying looks. To some that probably looks terrifying, but thanks to Emacs+Paredit it's a few handy keystrokes to type auto-complete and manipulate and automatically pretty-format such things, and thanks to a suitably large dose of Lisp brand Kool-Aid I find it very natural and comfortable to read at this point.

Then I can (csv ...) it or (plaintext-table ...) it or whatever. I replaced thousands of lines of Ruby and SQL queries with a few hundred lines of Clojure this way, and the Clojure version does more and does it better.

One of the things I like about Clojure is that it's such a small language, you can be reasonably sure you know the whole language (or at least have some passing familiarity with all parts of it) once you've read the docs and the API a few times. This is in contrast to languages like Common Lisp for example where the standard is thick enough to be considered a deadly weapon. Java lurks underneath but you can get away with ignoring it almost entirely, until those rare times you need it.

Alan Perlis said:

It is better to have 100 functions operate on one data structure than 10 functions on 10 data structures

This is true, but Clojure takes it further: It's even better to have a lot of functions that act on one abstraction of a bunch of data structures. Clojure gives you a bunch of data structures that can all be accessed under the same seq abstraction, and a bunch of functions that work on that abstraction, and the end result is more than the sum of the parts, because everything is interchangeable in lovely ways. I bounce data between sets and hash-maps and vectors without even thinking about it half the time.

That's just one reason of many that I love Clojure nowadays. I get crap done with it, quickly and easily and with surprising amounts of fun. Thanks Clojure and Clojure devs for making my life better.

October 17, 2009 @ 4:24 PM PDT
Cateogory: Programming
Tags: Ruby, Clojure