class Treetop::Compiler::Choice

def compile(address, builder, parent_expression = nil)
  super
  begin_comment(self)
  use_vars :result, :start_index
  compile_alternatives(alternatives, parent_expression)
  end_comment(self)
end

def compile_alternatives(alternatives, parent_expression)
  obtain_new_subexpression_address
  alternatives.first.compile(subexpression_address, builder)
  builder.if__ subexpression_success? do
    # Undo lazy instantiation:
    builder << "#{subexpression_result_var} = SyntaxNode.new(input, (index-1)...index) if #{subexpression_result_var} == true"
    assign_result subexpression_result_var
    extend_result_with_declared_module
    extend_result_with_inline_module parent_expression
  end
  builder.else_ do
    if alternatives.size == 1
      reset_index
      assign_failure start_index_var
    else
      compile_alternatives(alternatives[1..-1], parent_expression)
    end
  end
end

def expected
  '"(any alternative)"'
end