Containers, Blocks, and Iterators(Chapter 4 of Programming Ruby)

 def three_times

   yield

   yield

   yield

 end

 three_times { puts "Hello" }

 [1,3,5,7].inject(0) {|sum, element| sum+element} # => 16
2 [1,3,5,7].inject(1) {|product, element| product*element} # => 105
3 
4 [1,3,5,7].inject {|sum, element| sum+element} # => 16
5 [1,3,5,7].inject {|product, element| product*element} # => 105

 

 

 1 triangular_numbers = Enumerator.new do |yielder|
 2   number = 0
 3   count = 1
 4   loop do
 5     number += count
 6     count += 1
 7     yielder.yield number
 8   end
 9 end
10 
11 5.times { puts triangular_numbers.next }
12 1
13 3
14 6
15 10
16 15

 

 

 def n_times(thing)
2  lambda {|n| thing * n }
3 end
4 
5 p1 = n_times(23)
6 p1.call(3) # => 69
7 p1.call(4) # => 92
8 p2 = n_times("Hello ")
9 p2.call(3) # => "Hello Hello Hello "