How the Clojure Dojo worked in London

I ended up giving my clojure dojo http://learnclojure.blogspot.com/2010/01/clojure-dojo-method-of-heron-of.html twice at dev8d in London, after two dry runs in Cambridge. The results were as follows:

I In Cambridge to the BioInformatics Group of the Chemistry Department (8 people present for 1 1/2 hours)

Worked well, got as far as a general square root solver. Everyone stayed involved and I think everyone enjoyed it.

II In Cambridge to a man randomly encountered in a pub ( 1 person for 1 hour )

Worked a treat, got as far as a general square root solver. That will teach people to ask me what I'm doing when I look busy.

III In London at dev8d in an extra session organised in advance of the main event (5 people for 2 1/2 hours)

There was a non-native English speaker there, and the dojo format quickly proved its effectiveness. When he sat down at the keyboard it was obvious that he hadn't understood much of my introductory talk, but when he was forced to try to construct expressions at the REPL he quickly got the hang of it, and turned out to be very good.

We got through the square root finder very quickly, and then the group wanted to know about macros. I thought this was perhaps a bit much for people who'd only learned the language an hour ago, and instead led them through the symbolic differentiator, as an example of how LISP can process its own code. This is after all the basis of macros!

One girl out of the five had only the sketchiest notion of what a derivative was, so we made her do most of the typing in this second half.

Afterwards, when I pointed out that a program which takes code and gives back other code is usually known as a compiler, and that she'd just written one, her face lit up with pride. This was the most rewarding moment of the week for me.


IV In London at dev8d in the planned session (27 people for 2 1/2 hours)


With so many people it was very hard to keep everyone properly involved, and so we broke the rules and had people who already had a clojure setup working on their own laptops separately from the communal effort.

After an hour and a half or so we made our square root finder, and there was a big round of applause.


I should really have canned it there, but people were still keen and wanted to know more, so we pressed on to do the general Newton-Raphson method solver.

At that point it went a bit wrong:


I'd been expecting Newton's method to be common knowledge amongst programmers (I'm sure it was on my maths A-level), and so to be a nice simple example of how powerful the general iterative-improve strategy is.

But in fact the method seemed to confuse people, and they got distracted from the programming by trying to understand the algorithm. There were too many people in the room for me to make sure that everyone stayed on board.


Nevertheless, they got the thing done with not too much help from me. I think by the end I had lost some of my audience, and I was a bit disappointed.

But afterwards lots of people came up and told me how much they'd enjoyed it, and apparently there were a lot of positive comments made afterwards (I had spies planted to find out what people really thought.).

I suspect that some people loved it, and some people lost the plot and were bored. Sorry to those people! As they say, if someone isn't learning, someone isn't teaching....


I think next time I either need to find a less scary example (it wasn't meant to be scary!!) or find a better way of explaining the strategy without using the fear-inducing word "derivative"! That may in fact not be too hard. Something like 'try moving the guess a bit, and see how much difference that makes, ok how much does that mean we should change our guess by?'.

I'll also see if I can keep the numbers down to below ten for the next one. Then you can rescue people who are floundering rather than ignoring the fact so that the group can progress.

There will be a next time. Various friends have expressed interest, and I enjoyed doing it, so we'll organise some more sessions, and for the advanced students, I'll try and think of some suitable examples that will illustrate what's particularly good about Clojure, once people have got the hang of why LISP itself is so cool.