# frozen_string_literal: true

module MutualRecursion
  UNEXPECTED_TYPE = 'expected tail_call or terminal_value'

  class TailCall
    attr_reader :value, :block

    def initialize(value = nil, &block)
      @value = value
      @block = block
    end

    def invoke
      self.then do |tail|
        while tail.block
          tail = tail.block.call
          raise TypeError, UNEXPECTED_TYPE unless tail.is_a?(TailCall)
        end

        tail.value
      end
    end
  end
end

def tail_call
  MutualRecursion::TailCall.new { yield }
end

def terminal_value(value)
  MutualRecursion::TailCall.new(value)
end