An implicit class may not be top-level

[drdozer]

Top level declarations seem a bit hit and miss.

implied RunNNFExpr[B] for RunDSL[NNF[B], B] = _.terminal

implied RunNNFImpl[B] for RunDSL[NNF[B], B] {
  override def runDSL(b: NNF[B]): B = b.terminal
}

The top declaration RunNNFExpr works fine. The bottom declaration RunNNFImpl fails to compile with:

[error] 93 |implied RunNNF[B] for RunDSL[NNF[B], B] {
[error]    |^
[error]    |An implicit class may not be top-level
[error] 94 |  override def runDSL(b: NNF[B]): B = b.terminal
[error] 95 |}

This seems like a strange inconsistency.