class IRB::ExtendCommand::ShowSource

def execute(str = nil)
  unless str.is_a?(String)
    puts "Error: Expected a string but got #{str.inspect}"
    return
  end
  source = SourceFinder.new(@irb_context).find_source(str)
  if source
    show_source(source)
  else
    puts "Error: Couldn't locate a definition for #{str}"
  end
  nil
end