t6895b.scala:20: error: could not find implicit value for parameter e: Foo[[X]Bar[[X]Or[String,X],X]]
  implicitly[Foo[({type L[X] = Bar[StringOr, X]})#L]]
            ^
t6895b.scala:23: error: polymorphic expression cannot be instantiated to expected type;
 found   : [F[_]]Foo[[X(in type L)]Bar[F,X(in type L)]]
 required: Foo[[X(in type L)]Bar[[X]Or[String,X],X(in type L)]]
  barFoo(null) : Foo[({type L[X] = Bar[StringOr, X]})#L]
        ^
two errors found