Scala: Pattern match + string concatenation

Question

I've got a simple recursive function to convert a list of booleans to a string:

def boolsToString(lst: List[Boolean]): String = lst match {
    case Nil => ""
    case x::xs => x match {
      case false => "0" + boolsToString(xs)
      case true => "1" + boolsToString(xs)
    }
  }

This works, but I don't like the repetition of boolsToString. I'd like to do the string concatenation just once (after the case) :

  def boolsToString2(lst: List[Boolean]): String = lst match {
    case Nil => ""
    case x::xs => x match {
      case false => "0"
      case true => "1"
    } + boolsToString2(xs)
  }

but this is rejected by the Scala compiler: "';' expected but identifier found."

Is there another way to do the string concatenation just once, after the case?

janos · Accepted Answer · 2013-11-17 14:51:25Z

5

No need to reinvent the wheel. Iterables already have a method for joining items into a string, called mkString:

def boolsToString(lst: List[Boolean]) =
  lst.map(if(_) "1" else "0").mkString("")

edited Nov 17, 2013 at 14:51

answered Nov 16, 2013 at 8:59

janos

126k31 gold badges242 silver badges253 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Shadowlands · Accepted Answer · 2013-11-16 07:42:15Z

3

How about:

def boolsToString(lst: List[Boolean]): String = lst match {
    case Nil => ""
    case x::xs => (if (x) "1" else "0") + boolsToString(xs)
  }

answered Nov 16, 2013 at 7:42

Shadowlands

15.1k4 gold badges47 silver badges45 bronze badges

Comments

Frank Schmitt · Accepted Answer · 2013-11-16 07:58:53Z

1

I figured it out; the trick to get the original version working is to put extra parentheses around the body of the case:

def boolsToString2(lst: List[Boolean]): String = lst match {
    case Nil => ""
    case x::xs => (x match {
      case false => "0"
      case true => "1"
    }) + boolsToString2(xs)
}

But @Shadowlands' answer is so much nicer :-)

answered Nov 16, 2013 at 7:58

Frank Schmitt

30.5k13 gold badges79 silver badges111 bronze badges

Collectives™ on Stack Overflow

Scala: Pattern match + string concatenation

3 Answers 3

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related