Question

my Haskell* is a bit rusty, so i can imagine that I’m missing the obvious:

def any[A](s: Traversable[A], f: A => Boolean): Boolean = {
    s.foldLeft(false)((bool, elem) => bool || f(elem))
}

Does one of these properties apply to the it?

1. predefined somewhere in the Scala libs
2. circumstantial, and faster written as some one-liner
3. wrong (I didn’t test it, sorry ;))

---

*actually SML, but that’s 99% the same, but known by nobody under the sun.

Answer 1

1. It’s predefined and is called exists. And forall would be the “all” function you are looking for.

   scala> Vector(3, 4, 5).exists(_ % 2 == 0)
   res1: Boolean = true
   
   scala> Vector(3, 4, 5).forall(_ % 2 == 0)
   res2: Boolean = false
   

2. You can make it more performant using a for loop with a break (from scala.util.control.Breaks). (See the standard library implementation of exists and forall.)

3. It’s correct.