Trying to understand why mapping over a function with a context bound requires setting the type explicitly

implicit with map.scala

abstract class Ponies[T] {
  def ponies(a: T) : String
}

def bar[T](obj: T)(implicit p : Ponies[T]) = p.ponies(obj)
def baz[T](obj: T) = obj
def qux(obj: Int)(implicit p : Ponies[Int]) = p.ponies(obj)
def fred[T: Ponies(obj: T) = implicitly[Ponies[T]].ponies(obj)

def foo {
  implicit object IntCanHazPonies extends Ponies[Int] {
    def ponies(a: Int) = s"$a can haz ponies!"
  }

  // These fail with
  // "could not find implicit value for parameter p: this.Ponies[T]"
  // Some(2).map(bar)
  // Some(6).map(fred)

  // These all work
  bar(1)
  Some(3).map(bar[Int])
  Some(4).map(baz)
  Some(5).map(qux)
}

foo