scala - Fs2 Stream.Compiler 未找到(找不到隐含值 Compiler[[x]F[x],G])

Question

我正在尝试编译流，但不知何故Compiler不在范围内，需要什么上下文绑定(bind)才能将其纳入范围？

import cats.Monad

def compilingStream[F[_]: Monad]: F[List[Int]] = {
  val stream: fs2.Stream[F, Int] = fs2.Stream.emit(1).covary[F]
  stream.head.compile.toList
}


error: could not find implicit value for parameter compiler: fs2.Stream.Compiler[[x]F[x],G]
         stream.head.compile.toList
                     ^

Answer 1

FS2 Stream#compile现在需要 Sync[F] (见 this):

  import cats.effect.Sync

  def compilingStream[F[_]: Sync]: F[List[Int]] = {
    val stream: fs2.Stream[F, Int] = fs2.Stream.emit(1).covary[F]
    stream.head.compile.toList
  }

这是由库维护者传达的:

fs2 Stream#compile now requires a Sync[F]. Even on completely pure streams. Because of resource management. Sad. Panda.

Daniel Spiewak