“Introduction to Lazy lists” How to use and construct lazy lists on Programming Langage Ruby.

1. Introduction to Lazy Lists
2008 UJIHISA, Tatsuhiro

2. UJIHISA Tatsuhiro
• Osaka University
• Ruby, Vim, Haskell and Math
• http://ujihisa.nowa.jp
• http://twitter.com/ujm
• To the US!

3. Targets
•
• Array, Enumerable, IO (File)
Haskell

4. Lazy lists

5. • Ruby Haskell
(Lazy list)
Live coding
Vim

6. Lazy Lists
• Lazy lists (or streams)
• List (= Array in Ruby)
• Only needed parts are calculated.
• Haskell supports lazy lists by default.
• Ruby can support it.

7. List (=Array) in Ruby
• Array class
• [0, 1, 2, 3], Array.new(4) {|i| i }
• a #=> [0, 1, 2, 3]
a.map {|i| i * 2 } #=> [0, 2, 4, 6]

8. List
• Data structure
• Insert, Delete, Access sequentially

9. c.f. Array
• Data structure
• Insert, Delete, Access randomly, Size

10. (List again)
• Data structure
• Insert, Delete, Access sequentially

11. Lazy List
• Data structure
• Insert, Delete, Access sequentially

12. Types of lazy lists
• Boundless length lists ( )
• Undefined length lists ( )
• Defined length lists ( )

13. How to construct
lazy lists?

18. Notations
• array = 1000+ length array
heavy = lambda { heavy procedure }
• array.take(2).map(&heavy)
• array.map(&heavy).take(2)

22. Common case
• truncation (break)
• filtering (if, unless; select, reject)
• mapping (=, map)
• processing (???, each)
folding (<<, inject)