Question

I am new to Scala so trying to do the simple thing first.

I wrote a method which is below.

//Given a list of numbers find the first number that is a multiple of 7
  def FindFirstMultiple(input: List[Int]) : Int  = {   
    for (
        i <- input        
        if (i % 7 == 0)
       ) 
      return i        
  }  

This method gives error

type mismatch;  found   : Unit  required: Int   

I am not able to comprehend this. When I don’t have a return type and just print the values, it works fine.
Also, Why does the error squiggly hover over i <- input. I think the Scala compiler is trying to tell me something, and I just can’t understand it. What would be the cause of this error ?

Answer 1

for in Scala is not a for loop, in fact it’s not a loop at all. It’s a syntactic sugar for map and flatMap and other monadic goodies. Monads are very useful in functional programming, i recommend invest some time learning them; you can start at http://james-iry.blogspot.com/2007/09/monads-are-elephants-part-1.html , follow the whole series.
Thanks to the wonderful Mr James Iry.

If you just want the first item that matches your query, try this

val findFirst:Option[Int] = input.find(i => i % 7 == 0)

Posible values for findFirst are

1. Some(n) if something was found, where n is the Int found
2. None if nothing was found