Laziness - or code as data!

1-with-lambdas.rb

shout  =->(name) { "HELLO #{name.upcase}!" }

def greet(name, greeter)
  greeter.call(name)
end

puts greet("Robert", shout)  #=> HELLO ROBERT!

2-with-a-custom-class.rb

module BackwardsGreeter
  extend self
  def greet(name)
    "Hello #{name.chars.reverse.join.capitalize}."
  end
  alias_method :call, :greet
end

def greet(name, greeter)
  greeter.call(name)
end

puts greet("Robert", BackwardsGreeter)  #=> Hello Trebob.

3-with-a-complex-class.rb

# This was test driven enough to get through basic examples, it would fall apart
# on something like 'olga' but I wasnt trying to show how to TDD pig latin
module PigLatinGreeter
  extend self
  def greet(name)
    "Ellohay #{piggify(name)}."
  end
  alias_method :call, :greet

private

  def piggify(word)
    pigged = [first_half(word), second_half(word), "ay"].join
    pigged.capitalize
  end

  def first_vowel_position(word)
    word.gsub(/#{vowels}.*$/, '').size
  end

  def first_half(word)
    word.chars.drop(
      first_vowel_position(word))
  end

  def second_half(word)
    word.chars - first_half(word)
  end

  def vowels
    %w[a e i o u]
  end

  def consonants
    letters - vowels
  end

  def letters
    ('a'..'z').to_a
  end
end

def greet(name, greeter)
  greeter.call(name)
end

puts greet("Robert", BackwardsGreeter)  #=> Hello Trebor.