from() v2

def from(initial: Stream[(Block, List[Move])],
	  explored: Set[Block]): Stream[(Block, List[Move])] = initial.headOption.map {
  case (block, _) if done(block) => initial.head #:: from(initial.tail, explored)
  case (block, history) =>
    val newMoreBlocks = newNeighborsOnly(neighborsWithHistory(block, history), explored)
    val newExploredBlocks = Set(block.left, block.down, block.right, block.up).filter(_.isLegal).filterNot(done)
    (block, history) #:: from(initial.tail ++ newMoreBlocks, explored | newExploredBlocks)
  }.getOrElse(Stream())

fix unneeded tail evaluation