I notice my pace has yet again slowed between the last chapter of the book - Erlang - and this one. Another five months has passed since I finished the chapter on Erlang! In actual fact, I haven't been slaving away on the next language that whole time - decompression of sorts has to follow each chapter, and dealing with a manic three-year-old, finding some time for a bit of exercise and trying to learn a spoken language (German) all take a decent amount away from my free time.

The sixth chapter of Seven Languages in Seven Weeks is Clojure - a challenging language, but after getting through the previous five chapters this one only took me about three weeks of real world time (spent on-and-off) to conquer the last exercise of the chapter.

Since I tend to ramble on about the experiences I had while learning the new language, I'm going to break it down into a series of (hopefully) short points - what I liked about it and what I disliked. Do bear in mind that I'm no expert in Clojure, with only a brief learning period dedicated to it.

What I liked:

• It seems to have everything. The transactional memory support, power/libraries/community of the JVM, and many programming paradigms baked into the one language. This felt a lot like my experience with Scala, and I'm not sure if it is due to the JVM powering the runtime or the intents of the creators of the language.
• What I learned previously about how to best utilise recursion from Prolog and Erlang was also quite applicable here (albeit in slightly different form using loop/recur).
• The Leiningen tool and its REPL make getting into Clojure relatively easy, without having to initially bother with much of the JVM-required compilation/classpathery stuff (which frankly, I still don't understand).
• After just a small amount of time, the initial perception of it all being a mountain of parentheses dissipates reasonably quickly (but not entirely). Prefix notation is actually not that bad.

What I disliked:

• Despite my last point in the section above, parentheses and punctuation remain a big problem to newcomers to the language. If you are not used to Lisp-based languages, there is a big learning curve here. Similar to Scala, I found the large amount of other punctuation (which is used extensively in the language core as well) to be quite hard to understand. Some areas that provide interoperability with Java also have their own unique operators which makes it even harder to wrap your head around.
• There are often several ways to do things which are not obvious to a newcomer (e.g. creating classes with deftype vs defrecord vs a regular map, or when to use atoms vs refs vs other blocking data structures from the Java library). Some are still listed as experimental alpha features. Fortunately there are plenty of resources out either via Google or Stackoverflow.
• The language is powerful and sophistication, but I think this requires a corresponding amount of sophistication on the part of the programmer to use it without constructing a monstrosity. Macros take a while to wrap your head around (and I still couldn't tell you with certainty exactly when things need to be quoted and when not).
• Without being very familiar with Java (and its libraries) or the JVM, I felt at a disadvantage. I think a lot of parts of Clojure and Scala are framed in terms of how they wrap around the JVM, or solve a Java problem in a better or more understandable way than simply standing on their own. If you want to use the extensive Java interoperability then you have no choice but to learn how that works and its requirements (and with such extensive facilities on the Java side, it frequently makes sense to use the Java interop).
• To me it just doesn't feel like a great general-purpose language, but that is probably just because it seems quite academic. I can't imagine doing very rapid iteration web-app development in it, for example (although I know some people at my work that are doing just that). I guess what it comes down to, is that you would need a lot more experience in this language than you would if you were to pick up Ruby and start developing with Rails for example.

If this all seems like I'm not in favour of the language, that's not the case at all. Despite its challenges, I see Clojure as a very tempting and powerful language. If I were suddenly in a position where I had to do 100% of my coding in this language, I would see it as a good thing. For the moment though, there are simpler languages that accomplish everything that I need, and I don't feel the desire to become an expert in every language I have managed to familiarise myself with.

Sidebar: Spoken vs Programming Languages

After doing this much study on a variety of programming languages I don't use on a day-to-day basis, and having been learning German for a few years now (with varying levels of dedication) I've naturally been comparing how learning and knowledge of the two different types of language differs. I'll preface everything I say below with the fact that I'm not a linguist and haven't researched this topic academically whatsoever.

Firstly, there exists a certain type of programmer, computer nerd, systems engineer, etc. that will list (somewhat facetiously) their known languages (e.g. on Facebook, LinkedIn etc.) like this - English, German (or some other spoken language), Pig Latin, C, Python etc. etc. Maybe even Klingon. Their argument is that all languages are equivalent and that they know C just as well as they do English. The intent of listing languages in these data fields is usually just for natural spoken languages, but they have mixed the two "types" of language together.

To the majority of us, this argument is plainly false. I recall briefly reading some discussion on this from actual linguists, and at a purely biological level, using spoken languages and computer languages exercise completely different parts of the brain. There are different amounts of reasoning, analysis and plain communication going on depending on whether you are speaking to another human being or expressing an algorithm to a computer.

The grammar of spoken languages is complex, has many exceptions, idioms, and is constantly evolving, whereas in computer languages it is extremely well defined, seldom changes and must be understood by the computer and programmer in 100% of cases. Spoken languages have tens or hundreds of thousands of words, whereas computer languages often have just dozens or hundreds of identifiers at their core. Fluency is defined in a spoken language as basically needing no assistance to communicate with anyone in that language, whether it be spoken or written; even warping the language outside of its usual boundaries while remaining understood by other fluent speakers. Fluency in a computer language, it could be argued, might still permit a user of the language to consult references from time to time. Computer languages are also almost exclusively written, permitting more leisurely consideration of the correct grammar, syntax and vocabulary with which to express one's self.

This seems like a fairly compelling argument for the two types of language to be vastly different, but recently I've been thinking more and more about another level of similarities beyond those points I've raised above. I would argue that true fluency in a computer language would in fact allow you to converse (perhaps not exclusively) with another fluent "speaker" of that language in actual spoken words, without aid of references. Anyone who has taken an interview at Google would know the requirement for whiteboarding a solution to a given problem in the language of your choice. You have no option but to be able to express yourself instantaneously, without references, and without making any mistakes - much like natural spoken languages.

Once you take into account all of the standard libraries, commonly used libraries outside of that, frameworks, extensions, plugins etc of a given computer language, the vocabulary is extended dramatically past the dozens or hundreds of words barrier. You can even draw a parallel between learning a given framework in a computer language, and becoming a specialist in a given occupational field - medicine for example introduces a new range of specialist language, just as the next new web-app framework might in your computer language of choice.

When speaking a computer language, the barrier for understandability is actually in some ways higher than than for natural spoken languages with a human partner. A human has the benefit of context, shared common knowledge and culture, observable body language, and can grant understandability concessions when the grammar, vocabulary or syntax is not entirely correct but can be inferred. A computer knows none of these and will not accept anything less than 100% accuracy.

Computers are hard, cold, reasoning machines and computer languages are expressly designed to convey meaning as efficiently as possible and with little room for interpretive error. Spoken languages are the result of centuries or millennia of evolution and culture, not to mention the development and psychology of the human brain itself. In some ways it is amazing that they are able to be compared at all, given their origins are so vastly different.

After dedicating my little free time over the last three weeks to Clojure it is now back to German until I have finished the current teaching book I'm working through. The unifying factor for me personally is that I find learning both spoken and computer languages challenging, mind-bending but exciting. I have no intention of becoming "fluent" in more than a very small amount of programming languages (a passing familiarity is probably sufficient) but I would be significantly upset if I never become fluent in German.

On a related note, if you haven't yet checked out Hello World Quiz, it is frustrating but simultaneously a lot of fun :)