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Not Everything Is An Object

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A presentations highlighting the weaknesses in OO programming and showing how functional languages, in this case Clojure, could be the answer.

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Not Everything Is An Object

  1. 1. Not Everything is an Object<br />By @garyshort<br />
  2. 2. Agenda<br />The road to here<br />Where we are now<br />What OOD/P is good for<br />What it’s not good for<br />The solution<br />Demo<br />Questions.<br />
  3. 3. The Road to Here<br />http://www.flickr.com/photos/fyngyrz/<br />
  4. 4. Where we are Now<br />http://www.flickr.com/photos/gtarded/<br />
  5. 5. What OOP/D is Good For<br />http://www.flickr.com/photos/gserafini/<br />
  6. 6. What is it Not Good For?<br />http://www.flickr.com/photos/aloshbennett/<br />
  7. 7. The Solution<br />
  8. 8. What Does it Mean to be Functional?<br />First order functions<br />Function like constructs<br />Stateless<br />Immutable data.<br />
  9. 9. Clojure<br />A Lisp<br />Dynamic<br />Functional<br />Impure<br />“Lockless” Concurrency<br />Macros<br /><ul><li>JVM
  10. 10. Java Interop
  11. 11. Fast
  12. 12. Persistent collections
  13. 13. Easy to learn.</li></li></ul><li>Introduction to Clojure<br />Java.Lang.Object<br />Arbitrary sized numbers<br />Ratios: 18/20<br />Nil is null and is treated as false.<br />
  14. 14. Persistent Collections<br />Immutable<br />Cheap to copy<br />Examples<br />(1 2 3)<br />List – sequential lookup time<br />[1 2 3]<br />Vector – logarithmic lookup time<br />{“key” 1, 3 7, “foo” “bar”}<br />Hashmap – unordered, key value pairs.<br />
  15. 15. Equality Vs Identity<br />Equality<br />Two objects are equal<br />Two cylinders maybe equal if their volumes are equal<br />Identity<br />Two pointers to the same object<br />Clojure favours equality :-O.<br />
  16. 16. Clojure is Impure so has Mutability<br />Var<br />Mutable pointer to immutable data<br />You can’t change the data<br />But you can change what data the var points to<br />But vars hold global data, function defs etc .<br />This data won’t change<br />So why are vars mutable?<br />So we can patch running software. <br />
  17. 17. The Reader<br />Other programming languages<br />Compiler<br />Text -&gt; lexing and parsing -&gt; AST<br />Clojure<br />The Reader<br />Text -&gt; lexing and parsing -&gt; Literals (Data)<br />As soon as it reads a complete literal it’s passed to...<br />
  18. 18. The Evaluator<br />Compile Phase<br />Traverses the data<br />Symbol evaluation<br />Symbols evaluate into Vars<br />Symbol Dog evaluates to a var in the current namespace<br />Symbol MyPets/Dog evaluates to var in namespace MyPets<br />List evaluation<br />Lists evaluate into function calls<br />(+ 1 2 3)<br />Process macros<br />Execute phase<br />Effects the special forms<br />Calls functions.<br />
  19. 19. Special Forms<br />Reserved symbol<br />Denotes special list evaluation<br />Not a function call – it’s “something else”<br />Def, if, do, let, quote, var, fn, loop, recur, throw, try, ., new, set!<br />If a list starts with any of those it’s evaluated in a special way particular to that form<br />(if condition a b?)<br />(if (been_drinking) (hungover) (happy))<br />(if (have_beers) (drink))<br />
  20. 20. Tail Recursion<br />http://www.flickr.com/photos/43911015@N05<br />
  21. 21. I’m Bored... Show me the Code!<br />http://www.flickr.com/photos/peter_hasselbom/<br />
  22. 22. Questions?<br />gary@garyshort.org<br />www.garyshort.org<br />@garyshort<br />

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