gistfile1.txt

trait Eq[-T] 

def equal[T](left : T, right : T)(implicit eqT : Eq[T]) = true

implicit def eqInt = new Eq[Int]{}

trait List[T]

implicit def eqList[T](implicit eqT : Eq[T]) = new Eq[List[T]] {}

class ListListInt extends List[List[Int]]

def ints = new ListListInt

equal[List[List[Int]]](ints, ints)
equal[ListListInt](ints, ints)
equal(ints, ints)

/*
Works in Scala versions >= 2.8.1
Fails in 2.7.7, 2.8.0:

scala> equal[List[List[Int]]](ints, ints)
res2: Boolean = true

scala> equal[ListListInt](ints, ints)
<console>:13: error: diverging implicit expansion for type Eq[ListListInt]
starting with method eqList in object $iw
       equal[ListListInt](ints, ints)
                         ^

scala> equal(ints, ints)
<console>:13: error: diverging implicit expansion for type Eq[ListListInt]
starting with method eqList in object $iw
       equal(ints, ints)
            ^
*/