Pattern match for Integer range

Question

The purpose of my function is to add 5 to an integer as long as that integer is greater than 0 and less than or equal to 7. I try:

val add5Partial : PartialFunction[Int, Int] = {
  case d if (0 < d <= 7) => d + 5;
} 

I get:

<console>:8: error: type mismatch;
 found   : Int(7)
 required: Boolean
         case d if (0 < d <= 7) => d + 5;

Any tips?

Answer 1

Scala do not support such syntax out of the box, so you have to write:

val partial : Int => Int = {
  case d if (d > 0) && (d <= 7) => d + 5;
} 

Alternatively you could do:

val partial : Int => Int = {
  case d if 1 to 7 contains d => d + 5;
} 

Answer 2

You can't do this in a single comparison. You need to use:

(d > 0) && (d <= 7)

As you have done it, it will evaluate one comparison to a Boolean and then fail to use this as an int in the second comparison.

Answer 3

You can do any of the following:

val f = (n: Int) ⇒ if (n > 0 && n <= 7) n + 5 else n

// or ...

def f(n: Int) = if (n > 0 && n <= 7) n + 5 else n

// or ...

def f(n: Int): Int = n match {
    case n if n > 0 && n <= 7 ⇒ n + 5
    case _ ⇒ n
}

// or (to speak of ... the comment by @om-nom-nom)

def f(n: Int) = n match {
    case n if 0 to 7 contains n ⇒ n + 5
    case _ ⇒ n
}