Intro to Clojure - Week 1

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Ian Bishop @ianbishop

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Studied at UNB (CS/Math) Work at UserEvents Open Source (Official Clojure ZMQ) (Unofficial Clojure LMAX Disruptor)

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Modern dialect of Lisp Created by Rich Hickey in 2007 General purpose functional language Runs on a number of platforms (JVM, CLR, Javascript)

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Modern dialect of Lisp Created by Rich Hickey in 2007 General purpose functional language Runs on a number of platforms (JVM, CLR, Javascript)

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baby

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Invented in 1958 by John McCarthy Second oldest modern programming language Introduced fundamental ideas of modern programming Tree Data Structures Garbage Collection Dynamic Typing Conditionals Recursion Higher-order functions

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the greatest single programming language ever designed Alan Kay, creator of Smalltalk & Object Oriented programming

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the greatest single programming language ever designed Alan Kay, creator of Smalltalk & Object Oriented programming

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Some may say Ruby is a bad rip- off of Lisp or Smalltalk, and I admit that. But it is nicer to ordinary people Matz, creator of the Ruby programming language

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Some may say Ruby is a bad rip- off of Lisp or Smalltalk, and I admit that. But it is nicer to ordinary people Matz, creator of the Ruby programming language

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any sufficiently complicated C or Fortran program contains an ad hoc informally- specified bug-ridden slow implementation of half of Common Lisp Philip Greenspun

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any sufficiently complicated C or Fortran program contains an ad hoc informally- specified bug-ridden slow implementation of half of Common Lisp Philip Greenspun

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Lisp is worth learning for the profound enlightenment experience you will have when you finally get it; that experience will make you a better programmer for the rest of your days, even if you never actually use Lisp itself a lot. Eric Raymond, Essayist & Open Source demigod

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I suppose I should learn Lisp, but it seems so foreign Paul Graham, Author of “On Lisp” & creator of Y Combinator

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I suppose I should learn Lisp, but it seems so foreign Paul Graham, Author of “On Lisp” & creator of Y Combinator

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(f arg0 arg1 arg2)

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(+ 1 2 3)

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(+ 1 2 3) => 6

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(list 1 2 3)

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(list 1 2 3) => (1 2 3)

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(if (= 1 1) (list 1 2 "foo") (list 1 2 "bar"))

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(if (= 1 1) (list 1 2 "foo") (list 1 2 "bar")) => (1 2 "foo")

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(lambda (x) (+ x 1))

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((lambda (x) (+ x 1)) 5)

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((lambda (x) (+ x 1)) 5) => 6

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(* 2 (+ 3 4))

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Abstract syntax tree is isomorphic to the textual representation of the language

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Abstract syntax tree is isomorphic to the textual representation of the language

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Abstract syntax tree is isomorphic to the textual representation of the language

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Abstract syntax tree is isomorphic to the textual representation of the language

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…

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code = data

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code = data data = code

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Reducing incidental complexity is a primary focus of Clojure. For example, mutable state is an incidental complexity. The mechanics of it seem simple, or at least familiar, but the reality is quite complex. So, Clojure makes immutable data the default. Rich Hickey, creator of Clojure

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cat.setName("Felix"); cat.getName(); => "Felix"

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cat.setName("Felix"); cat.getName(); => "Felix" cat.setName("Mr. Meowsworthy"); cat.getName(); => ??

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cat.setName("Felix"); cat.getName(); => "Felix" cat.setName("Mr. Meowsworthy"); cat.getName(); => "Mr. Meowsworthy"

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String s = "Mr. Meowsworthy"; s.replaceAll("Mr", "Mrs"); s => ??

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String s = "Mr. Meowsworthy"; s.replaceAll("Mr", "Mrs"); s => "Mr. Meowsworthy"

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Inventing a class with its own interface to hold a piece of information is like inventing a new language to write every short story. This is anti- reuse, and, I think, results in an explosion of code in typical OO applications. Rich Hickey, creator of Clojure

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com.sun.java.swing.plat.nimbus InternalFrameInternalFrameTitlePaneInternalFrameTitle PaneMaximizeButtonWindowNotFocusedState

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InternalFrame InternalFrame Title Pane, InternalFrame Title Pane. Maximize Button Window, Not Focused State.

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As you've noted, existing languages change slowly, if at all. Are we getting better languages? Many of the hot 'new' languages like Haskell and Erlang are in fact pretty old. Clojure builds on Lisp, which is really old. What is new is the willingness to utilize these languages in mainstream production environments. And that is a great thing, as we have largely maxed out the expressive capabilities of the C++/Java/C# languages, as evidenced by the prominence of XML and IDEs. Rich Hickey, creator of Clojure