Yes, it's possible! But not really very pretty:
trait Writer[T, O] {
def write(t: T): O
}
def writeToString[T: ({ type L[x] = Writer[x, String] })#L](t: T) =
implicitly[Writer[T, String]].write(t)
implicit object intToStringWriter extends Writer[Int, String] {
def write(t: Int) = t.toString
}
And then:
scala> writeToString(1)
res0: String = 1
The ({ type L[x] = Writer[x, String] })#L
thing is called a type lambda. Sometimes they're very convenient (if buggy), but this definitely isn't one of those times. You're much better off with the explicit implicit.