Question

假设具有带有不同签名的抽象方法的特征（请参见下文）。为了理解，我可以为每个抽象方法定义相同的签名Result[A]。

但是，为了简化trait的子类，我想保留方法2和3的简单签名。

import cats.data.{EitherT, Reader}
trait Domain{

   type  Read[A] = Reader[BoundsProblem, A]
   type Result[A] = EitherT[Read, String, A]

    def stepSize( s: State, direction: Direction): Result[Double] //depends on an injected context, can fail
    def takeStep( s: State, dir: Direction, stepSize: Double): Read[Variable] //depends on context, can't fail
    def calculate(x: Variable): (Double, Gradient) //context-independent, can't fail

     //doesn't compile: 
   def iteration(s: State, dir: Direction) =  for{
          tee <- stepSize(s, dir)
         x <- takeStep(s, dir, tee)
          r <- calculate(x)
      } yield  r
 }

我的问题是如何在Cats中完成此操作。（我将takeStep提升为EitherT[Read, String, A]的尝试没有成功。）还是我最好为每种方法都定义相同的Result[A]？

Answer 1

尝试

def iteration(s: State, dir: Direction): Result[(Double, Gradient)] =  for{
  tee <- stepSize(s, dir)
  x   <- EitherT.right(takeStep(s, dir, tee))
  r   = calculate(x)
} yield r

或

def iteration(s: State, dir: Direction): Result[(Double, Gradient)] =  for{
  tee <- stepSize(s, dir)
  x   <- EitherT.right(takeStep(s, dir, tee))
} yield calculate(x)

Scala猫中Monad变压器的提升功能

1 个答案: