Becoming Functional

I’ve been playing with the idea of doing some functional programming for a while now. I’ve been trying to learn and paddling around in the shallows but this week I dived right in the emacs/CIDER pool. I was aware of some dangers lurking beneath the surface: recursion, immutable data structures and the functional holy trinity of map, reduce & filter, so I came up with some ideas to face my fears. I’ve also realised my maths has got rusty so: Some of That Too.

  1. I’ve ‘done recursion’ before but I thought I’d read that my chosen weapon Clojure didn’t do tail-end recursion. This isn’t true. What it can’t do is automatic optimisation of tail-end  recursion, to stop it blowing the stack after a few thousand iterations but Clojure has a ‘recur’ expression to manually signal tail recursion and fix that. I knocked off the programme in a couple of hours and went to bed happy. My code was happily printing the first n numbers of the Fibonacci sequence but a day later I still couldn’t get it the return the numbers as a sequence.
  2. I was finding out about immutable data the hard way. You can’t build up an immutable vector, 1 element at a time. You get to keep the empty vector you created first. It’s a big mind-set change to not have variables that can vary. In my next post, I’ll try to say what I’ve learned. On this occasion it was lazy sequences.
  3. I mentioned the Algorave in my last post. I only found out about that because of an idea I had for improving my theoretical understanding of music. I realised that I could write, for example, a function that would return the 1st, 3rd and 5th notes in a major scale, using a map function.While working the theory out, I found out that Lisps are already popular in the live-coding world.
  4. At Algorave, I was inspired by the live-coded graphics to try automatically generating some graphics too, to work out the maths of mapping triangular grids onto Cartesian co-ordinates. I need that for another idea.

Three basic working programmes in about a week. They aren’t ‘finished’ but is software ever? They have delivered value via increased Clue.


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