Lazy evaluation example in Ruby

lazy.rb

[1] (pry) main: 0> { key: :val }.fetch(:key, raise('Key does not exist'))
RuntimeError: Key does not exist

[2] (pry) main: 0> { key: :val }.fetch(:key) { raise('Key does not exist') }
=> :val

[3] (pry) main: 0> Array.new(3, rand(10))
=> [0, 0, 0]

[4] (pry) main: 0> Array.new(3) { rand(10) }
=> [3, 1, 5]

[5] (pry) main: 0> %i(a b c).map { |symbol| puts symbol }.detect { true }
a
b
c
=> nil

[6] (pry) main: 0> %i(a b c).lazy.map { |symbol| puts symbol }.detect { true }
a
=> nil