Y Combinator example in Ruby

y.rb

def apply_lots(function: ->(x) { x }, times: 1, initial: nil)
  y_combinator = ->(f) {
    ->(x) { x.(x) }.(
      ->(x) { f.(->(*v) { x.(x).(*v) }) }
    )
  }

  times_step = ->(partial_fn) {
    ->(fn, rem, acc) { rem.zero? ? acc : partial_fn.(fn, rem - 1, fn.(acc)) }
  }

  y_combinator.(times_step).(function, times, initial)
end

apply_lots function: ->(x) { x * x }, times: 4, initial: 2
# => 65536

apply_lots function: ->(_) { puts "derp" }, times: 10
# => nil
# derp
# derp
# derp
# derp
# derp
# derp
# derp
# derp
# derp
# derp