Scala中更好的函数输入/输出参数样式

Question

This code works fine so far but i don't like the tuples everywhere like this which leads to using _.1 and _2 etc which is less expressive. I can implement wrapper classes that which have more expressive names. Is there a better approach?

trait DrawingSteps {

  def prompt(savedCommands: List[Command]): IO[(List[Command], Unit)]
  def read(savedCommands: List[Command]): IO[(List[Command], String)]
  def parseAndAppend(in: (List[Command], String)): List[Command]
  def invoke(savedCommands: List[Command]): IO[(List[Command], Unit)]

  def drawingProgram(savedCommands:List[Command] = List()):IO[(List[Command],Unit)] = for {
    t <- prompt(savedCommands)
    rawCommand <- read(t._1)
    commands = parseAndAppend(rawCommand)
    output <- invoke(commands)
  } yield output._1  match {
    case (_:CommandIsQuit)::_  => FP.exit(output._1).run
    case _ => drawingProgram(output._1).run
  }
}

Answer 1

You can always use pattern matching to deconstruct case classes/tuples and give meaningful names instead of using tuple elements ( _1 ). Here is an example:

trait DrawingSteps {

  def prompt(savedCommands: List[Command]): IO[(List[Command], Unit)]
  def read(savedCommands: List[Command]): IO[(List[Command], String)]
  def parseAndAppend(in: (List[Command], String)): List[Command]
  def invoke(savedCommands: List[Command]): IO[(List[Command], Unit)]

  def drawingProgram(savedCommands:List[Command] = List()):IO[(List[Command],Unit)] = for {
    (inCmd, _) <- prompt(savedCommands)
    rawCommand <- read(inCmd)
    commands = parseAndAppend(rawCommand)
    (outCmd, _) <- invoke(commands)
  } yield outCmd match {
    case (_:CommandIsQuit)::_  => FP.exit(outCmd).run
    case _ => drawingProgram(outCmd).run
  }
}

I guess you could replace tuples with HLists if you find yourself having lots of tuples with arity greater than 2. Looking at your code you have lots of repetitive return types like IO[(List[Command], Unit)] which can be declared with type alias or could benefit from being refactored into a case class for even better naming.