code.scala

    "compute FIRST for binary alternatives" in check { (left: String, right: String) =>
      import com.codecommit.util._
      
      val leftFirst = if (left.length == 0) Set[Char]() else Set(left charAt 0)
      val rightFirst = if (right.length == 0) Set[Char]() else Set(right charAt 0)
      
      if (leftFirst.size == 0 || rightFirst.size == 0)
        (left | right).first eq UniversalCharSet
      else
        (left | right).first == (leftFirst ++ rightFirst)
    }