型引数の部分適用

foo.md

class Foo {
  type L[A] = Either[String, A]
  foo[L](bar)
}

　↓

class Foo {
  type Anonymous = {type L[A] = Either[String, A]}
  foo[Anonymous#L](bar)
}

　↓

class Foo {
  foo[({type L[A] = Either[String, A]})#L](bar)
}

　use kind-projector 　

class Foo {
  foo[Either[String, ?]](bar)
}