Clojure Zipper

A lightning talk about the Zipper data structure at the Clojure User Group Paris (http://www.meetup.com/Paris-Clojure-User-Group/events/149254382/)
Source code for the live coding : https://gist.github.com/jgrodziski/7589471

Transcript

1. Clojure!
   An Introduction to Zippers!
   !
   Clojure User Group Paris – Nov 2013!
   

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2. #whoami  
   Jérémie Grodziski
   Software Designer and Programmer
   @jgrodziski
   jeremie@grodziski.com
   blog.zenmodeler.com  
   www.redsen.fr/blog  
   

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3. What’s the problem?
   I have a tree
   I want to modify ONE node
   and don’t want to rebuild
   the whole tree
   3
   4 7
   2 4
   8 5 9 3
   6
   => Zipper
   

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4. History
   

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5. Zipper fundamentals
   •  Purely functional data structure
   •  Think of it as a breacrumb or a zipper,
   that remember every direction you took
   from the root but starting from where
   you are, like an inverted glove
   

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6. Zipper functions
   

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7. Zipper creation
   

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8. Example
   means
   []
   0 []
   1A 1B 1C []
   2A 2B 2C [] ...etc
   

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9. Zipper navigation
   

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10. loc, node and root
    A loc (location) point to the current node
    along with the context (up, left and
    right)
    think: « like a pointer » to a particular node
    in the tree
    (node loc) returns the node at the loc
    (root loc) returns the root node (and not
    the loc!)
    

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11. Zipper edition
    

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12. Under the hood
    •  Zippers stores its “implementation” in
    metadata
    

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13. One last thing
    If you just want to walk a tree:
    use tree-seq then clojure.walk functions
    

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