Scala: type hint for lambda

I'm refreshing scala. This looks very simple to me but I can't get it to run:

import java.nio.file.{FileSystems, Files}

object ScalaHello extends App {
    val dir = FileSystems.getDefault.getPath("/home/intelli/workspace")
    Files.walk(dir).map(_.toFile).forEach(println)
}

It throws error at the mapping lambda:

argument expression's type is not compatible with formal parameter type;
 found   : java.util.function.Function[java.nio.file.Path,java.io.File]
 required: java.util.function.Function[_ >: java.nio.file.Path, _ <: ?R]

I suspect it has something to do with providing type hints for the lambda but I can't find anything surfing Google. Much appreciated

Note that Files.walk returns a Java Stream, so map and forEach come from Java.

Assuming you are using Scala 2.12, your code will work if you either:

1. Update Scala version to 2.13 (no need to make any other changes in this case)
2. Specify return type of map:

Files.walk(dir).map[File](_.toFile).forEach(println)

3. Convert to Scala collections before calling map:

import scala.collection.JavaConverters._
Files.walk(dir).iterator().asScala.map(_.toFile).foreach(println)