找不到类型 EnvT

Question

我有以下未编译的代码：

trait DbSetup[F[_]] {

  type EnvT[A] = OptionT[F, A]

  def system: EnvT[Env]

  def user: EnvT[String]

  def password: EnvT[String]

  def address: EnvT[String]

}

object DbSetup {

  def read[F[_]: Monad](s: DbSetup[F]): EnvT[Configuration] = ???

}

编译器抱怨：

not found: type EnvT
[error]   def read[F[_]: Monad](s: DbSetup[F]): EnvT[Configuration] = ???
[error]                                         ^
[error] one error found
[error] (Compile / compileIncremental) Compilation failed

如何将类型 EnvT 导入 object 范围？

Answer 1

尝试

def read[F[_]: Monad](s: DbSetup[F]): s.EnvT[Configuration] = ???

找不到类型 EnvT

Type EnvT can not be found

scala

monads

monad-transformers