Scalaz Reader to ReaderT(Scalaz Reader to ReaderT)

 我无法更改的函数返回Scalaz Reader ， 
 
type Action[A] = Reader[Session, A]

def findAccount(s: String): Action[Account] = 
  Reader((session: Session) => Account(s))
 
 我想基于findAccount(...)创建一个新函数来返回ReaderT[Option, Session, A] 
 
type ActionT[A] = ReaderT[Option, Session, A]

def findAccountT(s: String): ActionT[Account] = findAccount(s).map(Option(_))
 
 因为最终我想这样做， 
 
def findAccBalT(accountNumber: String) = for {
  acc <- findAccountT(accountNumber)
  bal <- findBalanceT(acc)
}  yield bal
 
 我该怎么办？ 是否有意义？ 谢谢 
 
 全面披露， 
 
import scalaz._
import Scalaz._        

trait Session {
  def doSomething(): Unit
}

case class Account(number: String) extends AnyVal
case class Amount(value: Int, currency: String) 
case class DBSession() extends Session {
  override def doSomething = println("writing to db")
}

type Action[A] = Reader[Session, A]
type ActionT[A] = ReaderT[Option, Session, A]

def findAccount(s: String): Action[Account] = 
  Reader((session: Session) => Account(s))

def findBalance(account: Account): Action[Amount] = 
  Reader((session: Session) => Amount(333, "S$"))

// failed
def findAccountT(s: String): ActionT[Account] = findAccount(s).map(Option(_))

// failed
def findBalanceT(account: Account): ActionT[Amount] = findBalance(account).map(Option(_))

// failed
def findAccBalT(accountNumber: String) = for {
  acc <- findAccountT(accountNumber)
  bal <- findBalanceT(acc)
}  yield bal

A function which I cannot change returns Scalaz Reader,
 
type Action[A] = Reader[Session, A]

def findAccount(s: String): Action[Account] = 
  Reader((session: Session) => Account(s))
 
I want create a new function based on findAccount(...) to return ReaderT[Option, Session, A] as in
 
type ActionT[A] = ReaderT[Option, Session, A]

def findAccountT(s: String): ActionT[Account] = findAccount(s).map(Option(_))
 
because eventually I want to do this,
 
def findAccBalT(accountNumber: String) = for {
  acc <- findAccountT(accountNumber)
  bal <- findBalanceT(acc)
}  yield bal
 
How do I proceed? Does it make sense? Thanks
 
Full disclosure,
 
import scalaz._
import Scalaz._        

trait Session {
  def doSomething(): Unit
}

case class Account(number: String) extends AnyVal
case class Amount(value: Int, currency: String) 
case class DBSession() extends Session {
  override def doSomething = println("writing to db")
}

type Action[A] = Reader[Session, A]
type ActionT[A] = ReaderT[Option, Session, A]

def findAccount(s: String): Action[Account] = 
  Reader((session: Session) => Account(s))

def findBalance(account: Account): Action[Amount] = 
  Reader((session: Session) => Amount(333, "S$"))

// failed
def findAccountT(s: String): ActionT[Account] = findAccount(s).map(Option(_))

// failed
def findBalanceT(account: Account): ActionT[Amount] = findBalance(account).map(Option(_))

// failed
def findAccBalT(accountNumber: String) = for {
  acc <- findAccountT(accountNumber)
  bal <- findBalanceT(acc)
}  yield bal

原文：https://stackoverflow.com/questions/37641796