Clojure at a Bank – Moving from Java (2012)

Management has choices here, including simply making the best business will stay good enough, or even if it doesn't, prioritizing keeping an essential core of its technology people short of anything but completely closing down the unit.

One thing I've noticed that's very common in the long term success or failure of high tech companies is whether they kept their core technologists. Compare Microsoft to Lotus and perhaps Ashton-Tate (dBase). Companies like banks may not appear to be "high tech companies", but their "production" is done with computer systems so....

Especially in a functional language, if you architect your code well, e.g. avoiding large (lengthy) functions. You write a function, test it in the REPL, and forget about it. Until, of course, someone hands it data you weren't expecting. But here Clojure helps you a bit with it's effort to provide consistent interfaces to its collection types, e.g. lists, vectors and maps. And the most expressive and fast to write code in, the more time you can devote to testing.

I'll bet in practice this sort of TDD works very well, as long as your coders are diligent. For the projects I've done this way, including a couple in C using a very good but now defunct interpretive environment for it (CenterLine's CodeCenter/ObjectCenter), it's been superb. In an extreme case, I spent around a week programming in C the engine of a high speed document imaging scanning system, at which point I got the driver that let me speak directly to the scanner. The first time I tried it end-to-end it worked ... until I ran out of file descriptors (had forgotten to close() each file after writing out its contents).

There was of course a whole lot of experience that made that feat possible, but I found it very impressive how the environment allowed me to write code with so few flaws (that was, in fact, the only major one I can remember once I declared a function finished and ready to try out for real).

I'm sure Bell Labs never had that problem :) I was reading someone's PhD dissertation on Chill [1] and what was interesting to note was how many of the players ended up outsourcing their software development to 3rd parties.

Software is hard.

There other day I was talking with someone in tech management from a national chain (think malls). They are rolling their own commerce platform since "nothing" out there can satisfy their ecommerce requirements. I didn't say this upfront -- a potential client -- but the idea that this chain will actually get into serious software development, develop an A team, and keep them, is complete and utter wishful thinking.

My advice to anyone running a non-tech company is own the data and the apis and off load the rest to a[n] actual tech company.

[1]: http://web.bi.no/forskning/papers.nsf/0/42215f66b6282965c125...

Wrt the typing of Maps and Arrays, what Clojure supports goes way beyond what Java's type system supports: you can specify that the first element of an array has to be of type X, the second is of type Y, the third can be either NULL or Z. For maps, you can specify that a key must have a particular type and must be in the map, with a specific value while other keys may be present (required or not) and you can compose any of the constraints mentioned on the values the keys may take.

This is different from Generics in that Generics constrain to homogeneity for an entire collection.

You could create formal objects in your Java code to express similar constraints, but you're not achieving the same result: a Java object actually has the property (even if it's null) while a map (or an array) with an optional member will only have it if it's present. With Java you'd need many classes to model all the specific combinations. Java's current type system is significantly less expressive and doesn't have the same power. I realize those are subjective. By expressive and power I am referring to whether you can declare an idea in your code or whether you have to write the imperative logic to implement an idea (the former meeting my definition of expression or power).

Thanks for the question.