For loop mismatch in scala function

Question

I read the tutorials on how to write a for loop in scala but it doesn't seem to work.

object Main {
    def pascalTriangle(rows:Int):List[Int]= {
    var previousRow:List[Int] = Nil 
    var row:List[Int] = Nil
    for(i <- 1 to rows) {
        for( j <- 1 to i+1){
            if (j == 1 || j == i)
                row :+ 1
            else
                row :+ previousRow(j) + previousRow(j - 1)
            }
            previousRow = row
            println (row)
            row = Nil
        }
    }
     def main(args: Array[String]) {
        pascalTriangle(6)
     }
}

I keep getting a type mismatch error within the for loop's conditions.

you have a return type of List[Int]. but you are actually returning Unit. — Johny T Koshy
– Johny T Koshy, Commented May 23, 2014 at 3:59

Stephane Bersier · Accepted Answer · 2014-05-23 06:34:26Z

1

Your method pascalTriangle is declared to return a List[int].

However, the last expression in the body of the method is your outer for-loop. This is the expression whose value will be returned by the method.

As for-loops (that don't use the yield keyword) evaluate to (): Unit, there is a type-mismatch with the expected return type (for-loops without yield are used only for side-effect).

If you wanted to, for example, return row, you would need to simply write 'row' at the end of the method, after the outer for-loop.

answered May 23, 2014 at 6:34

Stephane Bersier

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