select.rb

module Selectable
  def recieve?; false; end
  def send?; true; end
end

class Channel
  include Selectable

  def recieve
    'hai'
  end
end

class Selector
  def initialize
    @cases = []
    @immediate = nil
    @default = nil
  end

  def default(&blk); @default = blk; end

  def case(condition, &blk)
    @immediate = blk if condition && !@immediate
    @cases.push blk
  end

  def select
    if @immediate
      @immediate.call
    elsif [email protected]?
      @default.call
    else
      p [@cases.size, :cases]
    end
  end
end

def select(&blk)
  s = Selector.new
  yield s
  s.select
end

c = Channel.new

select do |s|
  s.case(c.recieve?) { p c.recieve }
  s.case(false) { p 2 }
  s.default { p :default }
end

select do |s|
  s.case(c.recieve?) { p c.recieve }
  s.case(true) { p true }
end

select do |s|
  s.case(false) { p false }
end

puts "Done"

# :default
# true
# [1, :cases]
# Done