As it fell with a crash they looked that way, and the next moment all of them were filled with wonder. For they saw, standing in just the spot the screen had hidden, a little old man, with a bald head and a wrinkled face, who seemed to be as much surprised as they were. The Tin Woodman, raising his axe, rushed toward the little man and cried out, "Who are you?"

"I am Oz, the Great and Terrible,"

http://www.gutenberg.org/files/55/55-h/55-h.htm#chap16

For the experienced Java programmer we may seem to live in frightening times.  Functional programmers tell us that the world has become too complicated for us to understand.  Our careers might survive, if only we had lambdas, currying, higher-order functions, comprehensions and monads.

Functional programming has been described as an arcane, magicians art.  Take, for example, the opening of The Structure and Interpretation of Computer Programs:

In effect, we conjure the spirits of the computer with our spells.

A computational process is indeed much like a sorcerer's idea of a spirit. It cannot be seen or touched. It is not composed of matter at all. However, it is very real. It can perform intellectual work. It can answer questions. It can affect the world by disbursing money at a bank or by controlling a robot arm in a factory. The programs we use to conjure processes are like a sorcerer's spells.

http://mitpress.mit.edu/sicp/full-text/book/book-Z-H-9.html

For an example of arcane spells as incomprehensible as anything uttered by Albus Dumbledore you don't have to go far.  Consider Monads, for example.  Haskell has Monads, as does Scala.  So what is a monad?  Helpfully the Haskell Wiki explains everything:

Monads in Haskell can be thought of as composable computation descriptions. The essence of monad is thus separation of composition timeline from the composed computation's execution timeline, as well as the ability of computation to implicitly carry extra data, as pertaining to the computation itself, in addition to its one (hence the name) output, that it will produce when run (or queried, or called upon). This lends monads to supplementing pure calculations with features like I/O, common environment or state, and to preprocessing of computations (simplification, optimization etc.).

http://www.haskell.org/haskellwiki/Monad

Understanding Monads isn't just a simple case of learning or training.  It is a magical, spiritual experience.  This is why everybody who has every managed to understand them has written their own Monad tutorial.

[I]t seems like every programmer who gets monads posts a tutorial about them. (And each post begins with: There’s already a lot of monad tutorials on the Internet, but...) The reason is that getting monads it’s like a spiritual experience that you want to share with others. (Bartosz Milewski)

http://www.haskell.org/haskellwiki/Monad_tutorials_timeline

At the Code Shares we like to keep things simple and practical.  It doesn't matter how intimidating or confusing the words are, in the end it all has to be executed by a JVM.  A little JVM starting to show its age with a limited vocabulary of bytecodes.

The goal of May's Code Share is to ignore the big long explanations and take a look at how some of the functional features of languages like Scala or Clojure actually work.

May's Coding Challenge: Revealing the Magicians Secrets

The challenge for this month is to find an impressive one liner in a clever language and decompile it using a tool like JD, or Mocha.

What is actually going on?

What would the corresponding Java version look like?

Are these one liners just as efficient after compilation?

ABOUT VARIOUS SPEAKERS

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ABOUT THE LONDON JAVA COMMUNITY

The LJC is the Java User Group in London. It has over 3000 members and was founded in 2007 by Barry Cranford of RecWorks Ltd. The LJC is organised by a committee of passionate Java Enthusiasts. More about the London Java Community