A mixin with which to extend a singleton class that curries arguments on a function defined by `#def_function`.

curryable.rb

module Curryable
  def def_function &block
    @function = block
  end

  def call arg
    unless @function
      raise StandardError, 'must define a function with def_function'
    end

    function_chain.(arg)
  end

  private

  def function_chain *previous_args
    lambda do |arg|
      args = previous_args.dup << arg

      if terminate_chain?(args.size)
        @function.(*args)
      else
        function_chain(*args)
      end
    end
  end

  def terminate_chain? args_size
    (arity - args_size) == 0
  end

  def arity
    @function.arity
  end
end