The A-Z of Programming Languages: Clojure

Clojure creator Rich Hickey

Computerworld is undertaking a series of investigations into the most widely-used programming languages. Previously we have spoken to Larry Wall, creator of the Perl programming language, Don Syme, senior researcher at Microsoft Research Cambridge, who developed F#, Simon Peyton-Jones on the development of Haskell, Alfred v. Aho of AWK fame, S. Tucker Taft on the Ada 1995 and 2005 revisions, Microsoft about its server-side script engine ASP, Chet Ramey about his experiences maintaining Bash, Bjarne Stroustrup of C++ fame, and Charles H. Moore about the design and development of Forth.

We’ve also had a chat with the irreverent Don Woods about the development and uses of INTERCAL, as well as Stephen C. Johnson on YACC, Steve Bourne on Bourne shell, Tcl creator John Ousterhout, Falcon creator Giancarlo Niccolai, Luca Cardelli on Modula-3, Walter Bright on D, Brendan Eich on JavaScript, Anders Hejlsberg on C#, Guido van Rossum on Python and Prof. Roberto Ierusalimschy on Lua. We most recently spoke to Joe Armstrong, creator of Erlang.

In this interview, Clojure creator, Rick Hickey, took some time to tell Computerworld about his choice to create another Lisp dialect, the challenges of getting Clojure to better compete with Java and C#, and his desire to to see Clojure become a 'go-to' language.

If you wish to submit any suggestions for programming languages or would like to see a particular language authors interviewed, please email kathryn@computerworld.com.au

What prompted the creation of Clojure?

After almost 20 years of programming in C++/Java/C#, I was tired of it. I had seen how powerful, dynamic and expressive Common Lisp was and wanted to have that same power in my commercial development work, which targeted the JVM/CLR. I had made a few attempts at bridging Lisp and Java, but none were satisfying. I needed something that could deploy in a standard way, on the standard platforms, with very tight integration with existing investments.

At the same time, throughout my career I have been doing multithreaded programming, things like broadcast automation systems, in these OO languages, and seen nothing but pain. As a self-defense and sanity-preserving measure, I had moved my Java and C# code to a non-OO, functional style, emphasising immutability. I found this worked quite well, if awkward and non-idiomatic.

So, I wanted a dynamic, expressive, functional language, native on the JVM/CLR, and found none.

Where does the name Clojure come from?

It's a pun on the closure programming construct (and is pronounced identically). I wanted a name that involved C (CLR), L (Lisp) and J (JVM). There were no search hits and the domain was available - what's not to like?

Was there a particular problem the language aimed to solve?

Clojure is designed to support writing robust programs that are simple and fast. We suffer from so much incidental complexity in traditional OO languages, both syntactic and semantic, that I don't think we even realise it anymore. I wanted to make 'doing the right thing' not a matter of convention and discipline, but the default. I wanted a solid concurrency story and great interoperability with existing Java libraries.

Why did you choose to create another Lisp dialect instead of extending an existing one?

While Lisps are traditionally extremely extensible, I had made some design decisions, like immutability for the core data structures, that would have broken backward compatibility with existing Scheme and Common Lisp programs. Starting with a clean slate let me do many other things differently, which is important, since I didn't want Clojure to appeal only to existing Lispers. In the end Clojure is very different and more approachable to those having no Lisp background.

Why did you pick the JVM?

I originally targeted both the JVM and CLR, but eventually decided I wanted to do twice as much, rather than everything twice. I chose the JVM because of the much larger open source ecosystem surrounding it and it has proved to be a good choice. That said, the CLR port has been revitalised by David Miller, is an official part of the Clojure project and is approaching feature-parity with the JVM version.

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