在 Free monad 中使用任一

问题描述

我正在尝试使用一个作为使用 Free monad 的代数的结果，如下面的代码

  ///// Command
  sealed trait Command[A]

  type Result[A] = Either[Exception,A]

  object Command {
    case class Tell(line: String) extends Command[Result[Unit]]

    case class Ask(line: String) extends Command[Result[String]]

  }

  type App[A] = EitherK[Command,Log,A]

  def program(implicit L: logops[App],C: CommandOps[App]): Free[App,Unit] =
    for {
      _ <- L.show("start <ask>")
      name <- C.ask("What's your name?")
      _ <- L.show("start <tell>")
      _ <- C.tell(s"Hi <$name>,nice to meet you!")
      _ <- L.show("done.")
    } yield ()

...

问题是名字是一个Either，所以我得到了以下输出

L--- start <ask>
What's your name?
George
L--- start <tell>
Hi <Right(George)>,nice to meet you!
L--- done.

有什么想法吗？

谢谢

解决方法

在此链接中找到的解决方案

Scala Free Monads with Coproduct and monad transformer

我必须定义一个像下面这样的函数

{
"Placeholder" : {
"prefix": ","
}
}

并使用它代替 //function to require uncached function requireUncached(module) { delete require.cache[require.resolve(module)]; return require(module); } //message event callback with prefix let prefixes = requireUncached('./prefix.json'); let prefix = prefixes['G'+message.guild.id].prefix; //prefix is now the chosen prefix //message event callback for new prefix: //or guildCreate event could use default prefix let newPre = message.content.split(/ +/)[1]; let prefixes = requireUncached('./prefixes.json'); prefixes['G'+message.guild.id].prefix = newPre fs.writeFile('./prefixes.json',JSON.stringify(prefixes),err => { if(err) throw err; console.log(`Prefix saved as ${newPre}`) }) //you can modify this for guildCreate event //so that you won’t get error cannot //set property prefix of undefined 像下面这样

def liftFE[F[_],T[_],A,B](f: T[Either[A,B]])(implicit I: InjectK[T,F]): EitherT[Free[F,*],B] = EitherT[Free[F,B](Free.liftF(I.inj(f)))

并更改“程序”结果类型

Free.inject