class Treetop::Compiler::Optional

def compile(address, builder, parent_expression)
  super
  use_vars :result
  obtain_new_subexpression_address
  parent_expression.atomic.compile(subexpression_address, builder)
  
  builder.if__ subexpression_success? do
    assign_result subexpression_result_var
  end
  builder.else_ do
    assign_result epsilon_node
  end
end