Is there a brief syntax for executing a block n times in Scala?

Question

I find myself writing code like this when I want to repeat some execution n times:

for (i <- 1 to n) { doSomething() }

I\'m looking for

Answer 1

It can be as simple as this:

scala> def times(n:Int)( code: => Unit ) {
          for (i <- 1 to n) code
       }
times: (n: Int)(code: => Unit)Unit

scala> times(5) {println("here")}
here
here
here
here
here

Answer 2

With scalaz 5:

doSomething.replicateM[List](n)

With scalaz 6:

n times doSomething

And that works as you would expect with most types (more precisely, for every monoid):

scala> import scalaz._; import Scalaz._; import effects._;
import scalaz._
import Scalaz._
import effects._

scala> 5 times "foo"
res0: java.lang.String = foofoofoofoofoo

scala> 5 times List(1,2)
res1: List[Int] = List(1, 2, 1, 2, 1, 2, 1, 2, 1, 2)

scala> 5 times 10
res2: Int = 50

scala> 5 times ((x: Int) => x + 1).endo
res3: scalaz.Endo[Int] = <function1>

scala> res3(10)
res4: Int = 15

scala> 5 times putStrLn("Hello, World!")
res5: scalaz.effects.IO[Unit] = scalaz.effects.IO$$anon$2@36659c23

scala> res5.unsafePerformIO
Hello, World!
Hello, World!
Hello, World!
Hello, World!
Hello, World!

You could also say doSomething replicateM_ 5 which only works if your doSomething is an idiomatic value (see Applicative). It has better type-safety, since you can do this:

scala> putStrLn("Foo") replicateM_ 5
res6: scalaz.effects.IO[Unit] = scalaz.effects.IO$$anon$2@8fe8ee7

but not this:

scala> { System.exit(0) } replicateM_ 5
<console>:15: error: value replicateM_ is not a member of Unit

Let me see you pull that off in Ruby.

Answer 3

The Range class has a foreach method on it that I think is just what you need. For example, this:

 0.to(5).foreach(println(_))

produced

0
1
2
3
4
5

Answer 4

def times(f: => Unit)(cnt:Int) :Unit = {
  List.fill(cnt){f}
}

Answer 5

I'm not aware of anything in the library. You can define a utility implicit conversion and class that you can import as needed.

class TimesRepeat(n:Int) {
  def timesRepeat(block: => Unit): Unit = (1 to n) foreach { i => block }
}
object TimesRepeat {
  implicit def toTimesRepeat(n:Int) = new TimesRepeat(n)
}

import TimesRepeat._

3.timesRepeat(println("foo"))

Rahul just posted a similar answer while I was writing this...

Answer 6

You could easily define one using Pimp My Library pattern.

scala> implicit def intWithTimes(n: Int) = new {        
     |   def times(f: => Unit) = 1 to n foreach {_ => f}
     | }
intWithTimes: (n: Int)java.lang.Object{def times(f: => Unit): Unit}

scala> 5 times {
     |   println("Hello World")
     | }
Hello World
Hello World
Hello World
Hello World
Hello World