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?

om-nom-nom has the answer. To my knowledge, _no_ common modern programming language allows the kind of shorthand notation you used. Note, too, that you don't need the outer-most parentheses surrounding the guard expression and semicolons in Scala are very bad style! Also, only put a space to the left of a colon when you're using the context bound syntax. — Randall Schulz, Jan 13 '13 at 21:25
@RandallSchulz python can do this. Actually I've seen that somebody on scala mailing list done this with scala as well, but with some additional trickery. Cant find it now. — om-nom-nom, Jan 13 '13 at 21:46
Duplicate of http://stackoverflow.com/questions/1346127/can-a-range-be-matched-in-scala. — Glenn, Feb 12 '15 at 15:15

om-nom-nom · Accepted Answer · 2013-01-13T20:42:29.963

20

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;
}

edited Jan 13 '13 at 20:42

answered Jan 13 '13 at 20:33

om-nom-nom

score 5 · Answer 2 · answered Jan 13 '13 at 20:33

5

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.

answered Jan 13 '13 at 20:33

David M

pestilence669 · Answer 3 · 2016-07-15T01:19:13.377

4

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
}

edited Jul 15 '16 at 01:19

answered Jul 15 '16 at 00:46

pestilence669

3 Answers3