x.rb

class Chain
  class InvalidChain < Exception; end

  CHAINS = [
    "as_long_as",
  ]

  def initialize(*args, &block)
    @args = args
    @block = block
    @chain = []
  end

  def previous(previous)
    @chain = [previous, *@chain]
  end

  def try_chain
    chain_name = @chain.map(&:to_s).join('_')
    if CHAINS.include?(chain_name)
      send(chain_name, *@args, &@block)
    else
      raise InvalidChain
    end
  end

  def as_long_as(condition, action)
    action.call while condition.call
  end
end

def chain(method, *args, &block)
  x = args[0]
  unless x.is_a?(Chain)
    x = Chain.new(*args, &block)
  end

  x.previous(method)
  begin
    x.try_chain
  rescue Chain::InvalidChain
    x
  end
end

def as(*args, &block)
  chain(:as, *args, &block)
end

def long(*args, &block)
  chain(:long, *args, &block)
end

i = 0
as long as -> { i < 10 }, -> { puts i+=1 }