How I Lazy and You Can Ruby 2

Lightning talk on Ruby's Enmuerator::Lazy

Transcript

1. Stephen Caudill @voxdolo
2. How I Lazy And You Can Ruby 2
3. Enumerator::Lazy
4. lazy evaluation In computer programming, lazy evaluation is the technique of delaying an evaluation of any expression until a value is actually being used and also avoid repeated evaluations.
5. eager evaluation In computer programming, eager evaluation or greedy evaluation is the evaluation strategy used by most traditional programming languages. In eager evaluation, an expression is evaluated as soon as it is bound to a variable.
6. eager evaluation (1..Float::INFINITY).map do |i| i ** 2 end
7. IRB::Abort: abort then interrupt!
8. (1..Float::INFINITY).lazy.map do |i| i ** 2 end lazy evaluation
9. #<Enumerator::Lazy:#<Enumerator::Lazy: 1..Infinity>:map>
10. Enumerator::Lazy#force “When it absolutely, positively has to be there [right now]”
11. (1..Float::INFINITY).lazy.map do |i| i ** 2 end.force
12. IRB::Abort: abort then interrupt!
13. (1..Float::INFINITY).lazy.map do |i| i ** 2 end.take(10).force
14. (1..Float::INFINITY).lazy.map do |i| i ** 2 end.first(10)
15. [1,4,9,16,25,36,49,64,81,100]
16. Now wait just a cotton-picking minute
17. Why be lazy?
18. fibonacci = Enumerator.new do |enum| yielder = ->(n){ enum.yield n } yielder.call(a=0) yielder.call(b=1) loop do a, b = b, a + b yielder.call(b) end end Combinatorics .lazy
19. fibonacci.first(10) ! => [0,1,1,2,3,5,8,13,21,34]
20. (1..Float::INFINITY).lazy.select do |x| x ** 2 % 5 == 0 end.take(10).reduce(:+) ! => 275
21. Stephen Caudill @voxdolo