This is a talk I gave at CFCAMP 2012 in Munich. It's an introduction to Clojure for CFML developers and how to leverage Clojure from a CFML developer's point of view. There are various examples and demo code that's not on the slides, contact me if you're interested in it.

1. Clojure - an introduction
Kai Koenig
CFCAMP Munich 2012
*and some CFML

2. Me

4. Kai Koenig
Working with CFML since 1999
Developing for mobile since 2003
Recovering Flex developer being sucked into JS deeper and deeper
Recently rediscovered Functional Programming
bloginblack.de
2ddu.com
twitter.com/agentK

5. Agenda

6. 1. Why Functional Programming?
2. Why Clojure?
3. Some demos and (probably failing :-) live coding in
the Clojure REPL
4. A quick look at Clojure and CFML integration

7. Why Functional
Programming?

9. Who of you has a
traditional, old-school
CompSci or Maths
degree?

10. The ones among you who answered with “yes”
probably have dabbled with either of:
ML
Scheme
Haskell
Lisp
At some point during their degree.

11. I did. Haskell and ML *
* Kind of confused me, I couldn’t see the point and we had Java anyway - which was
much more awesome & could do OO & was the hipster language of the day ** &
you could write AWT and Swing apps and just because.
** The day was 1996; Java was at version 1.0.2; and I was in my first year of my
CompSci and Maths degree

12. What is it?
A programming paradigm based on functions as first-
class citizens and a theoretical concept called “Lamba
Calculus”.
Depending on the FP language you’re looking at,
features might vary, but there are a few common
themes in functional programming.

13. First-class and higher-
order functions

14. Function that can take other functions as arguments or
return them as results (e.g. d/dx - differential operator
in calculus to return the derivative of a function).
Higher-order vs. first-class: just a subtle difference -
previous is a mathematical concept, latter is a CompSci
term.

15. Pure functions

16. Functions without I/O and memory side effects.
1. result is constant with respect to the parameter list
2. function call can be performed in parallel, they can’t
interfere with each other; thread safety
3. compiler has much more freedom in the evaluation
strategy of expressions provided the whole language is
side effect-free.

17. Recursion

18. In functional languages, iteration (loops) are pretty
much exclusively done via recursion.
Recursion functions invoke themselves all over again.
Intermediate state is kept on a stack.

19. Other

20. Evaluation strategy (eager vs. lazy)
Type system (untyped lambda calculus vs. type lambda
calculus)

21. But hang on. The world is full of “state”.
And side-effects.
I mean - WTF?

22. State can (and has to) be simulated in FP.
Different languages use different concepts that still keep
the functional paradigm pure.
Monads (Haskell)
State passing style (A bunch of other FP languages)
Managed references (Clojure)

23. How does FP “feel”?

24. Fibonacci
iterative in Java

25. public static long itFibN(int n)
{
if (n < 2)
return n;
long ans = 0;
long n1 = 0;
long n2 = 1;
for(n--; n > 0; n--)
{
ans = n1 + n2;
n1 = n2;
n2 = ans;
}
return ans;
}

26. Fibonacci
recursive in Haskell

27. -- describe an infinite list based on the recurrence
relation for Fibonacci numbers
fibRecurrence first second = first : fibRecurrence
second (first + second)
-- describe fibonacci list as fibRecurrence with initial
values 0 and 1
fibonacci = fibRecurrence 0 1
-- describe action to print the 10th element of the
fibonacci list
main = print (fibonacci !! 10)

28. Fibonacci
recursive in Clojure

29. (def fib (lazy-cat [0 1] (map + fib (rest fib))))
execute:
(take 10 fib)

30. Moore’s law failed
Need for concurrency

31. State in imperative and
OO languages

32. OOP encapsulates state
Changes overwrite state
State has multiple observers
Concurrency requires locking
Locking is complicated

33. Let’s look at Clojure

34. Clojure: dynamically typed,
JVM-based Lisp dialect
(by Rich Hickey in 2007)

35. But... why?

36. REPL

37. ReadEvalPrintLoop

39. Some Clojure features

40. Code is data

41. Literals

42. Java Interop

43. List,Vector, Map and Set

44. Life without for-loops

45. What is it good for?

46. Big data & Analytics
Pattern Matching
Heavy concurrency, scalable systems
Hard problems (often related to formal math or
algorithmic work)

47. Clojure and CFML

48. CFML is Java, right?

49. There is cfmljure!
https://github.com/seancorfield/cfmljure

50. Where and how would
you use it?

51. One idea: Model in MVC apps
Why? Because Clojure allows you to express business
logic and model data extremely efficiently.
Or: when you need to be able to run certain code in a
highly parallelised environment.

52. Anyway - it’s fun :)

53. Get in touch
Twitter: @AgentK
Blog: http://bloginblack.de
Podcast (2 Developers Down Under): http://2ddu.com
About me: http://about.me/agentk