Self-defined Classes in one cell cannot be invoked in another cell

[TaoRuan]

I am trying to run some code with self defined classes in Scala. But when I try to use them in another cell, it said reference to List is ambiguous.

[parente]

I have a PR pending with a fix for certain uses of case classes in Spark executor run functions. I'm not sure if this covers the problem you're seeing. Can you provide an example of the code and a stack trace? Or did you mean to close this issue as you found a fix?

[TaoRuan]

@parente
Hello! Thanks so much for asking. Actually I did not find a fix. I closed the issue simply because I did not find a good way to upload my code. They look so ugly. Wait a minute please

[TaoRuan]

@parente

sealed trait List[+A]
case object Nil extends List[Nothing]
case class Cons[+A](head: A, tail: List[A]) extends List[A]
object List {
def sum(ints: List[Int]): Int = ints match {
case Nil => 0
case Cons(x,xs) => x + sum(xs)
}
def product(ds: List[Double]): Double = ds match {
case Nil => 1.0
case Cons(0.0, _) => 0.0
case Cons(x,xs) => x * product(xs)
}
def apply[A](as: A*): List[A] =
if (as.isEmpty) Nil
else Cons(as.head, apply(as.tail: _*))
}

def sum(ints: List[Int]): Int = ints match {
case Nil => 0
case Cons(x,xs) => x + sum(xs)
}

val x = List(1,2,3,4,5) match {
case Cons(x, Cons(2, Cons(4, _))) => x
case Nil => 42
case Cons(x, Cons(y, Cons(3, Cons(4, _)))) => x + y
case Cons(h, t) => h + sum(t)
case _ => 101
}

[TaoRuan]

Above is all the coding I put into one cell and it worked well with the outputs:

defined trait List
defined object Nil
defined class Cons
defined object List
sum: (ints: List[Int])Int
x: Int = 3

[TaoRuan]

However when I put exactly the same last part of the code in the next cell, it cannot work

[TaoRuan]

val x = List(1,2,3,4,5) match {
case Cons(x, Cons(2, Cons(4, _))) => x
case Nil => 42
case Cons(x, Cons(y, Cons(3, Cons(4, _)))) => x + y
case Cons(h, t) => h + sum(t)
case _ => 101
}


Output:
<console>:40: error: reference to List is ambiguous;
it is imported twice in the same scope by
import $line16$read.List
and import INSTANCE.List
       val x = List(1,2,3,4,5) match {
               ^
<console>:43: error: type mismatch;
 found   : Any
 required: String
       case Cons(x, Cons(y, Cons(3, Cons(4, _)))) => x + y
                                                         ^
<console>:44: error: type mismatch;
 found   : List[Any]
 required: List[Int]
       case Cons(h, t) => h + sum(t)
                                  ^

[TaoRuan]

Updated the code. Please have a look if possible

[mariusvniekerk]

did you redefine List? Pretty sure that the scala repl is going to get somewhat angry at that since as part of the repl everything in scala.Predef gets pulled into the class that gets built for evaluating a cell.

[TaoRuan]

@mariusvniekerk Thanks! That should be the problem.

[TaoRuan]

@mariusvniekerk I tried to run the code in the original Scala REPL but I need not redefine the class every time. Whenever I run the last part of code it can work smoothly. I had expected the same thing in Jupyter Notebook but it seemed to be hard