CODEWITHSUNDEEP
scalafunctional-programmingscala-collections
Ddota
Ddota

Reputation: 163

Function that takes a function and list and returns Boolean

I am relatively new to Scala functional programming. I have been following a few tasks, however, finding difficult to understand or implement the concept below.

Basically, I want write a function which takes a list and a function, and returns true if the function returns true for at least one item in the list. An example would be: hasMatch(isEven,List(1,2,3,5)) will return true, but hasMatch(isEven,List(1,3,5)) will return false.

A sample solution or hint is provided with the problem, as seen below:

def hasMatch (fn:(Int)=>Boolean,lst:List[Int]):Boolean = {
    lst.foreach ((x:Int) => if (fn(x)) return true)
return false
}

Could someone please explain the concept behind it or ways to implement it.

Upvotes: 1

Views: 1339

Answers (3)

joesan
joesan

Reputation: 15345

Your isEven function is going to determine the outcome of the hasMatch function. So assuming that your isEven function is defined like this:

def isEven(x: Int): Boolean = x % 2 == 0

You can now define your hasMatch function like this:

def hasMatch(fn: Int => Boolean, l: List[Int]): Boolean = {
  l.exists(elem => fn(elem))
}

You then call the function like this:

hasMatch(isEven, List(1,2,3,5))

Upvotes: 1

Dima
Dima

Reputation: 40500

The biggest problem with your implementation: return is a really bad thing in scala, and should (almost) never be used.

Also, there are more idiomatic ways to do what you want, rather than spelling out the imperative loop with foreach.

Here is one possibility:

  def hasMatch[T](lst: List[T])(fn: T => Boolean) = lst.exists(fn)

I added a type parameter to your definition, so that it works for any type, not just Int. Also, I made fn the last argument, and moved it into a separate list. It makes it easier to pass anonymous functions in: 

  if (hasMatch(List(1,2,3,4,5)) { _ > 5 }) println("There are elements greater than five")

Upvotes: 1

Kraylog
Kraylog

Reputation: 7553

def hasMatch(fn: Int => Boolean, lst: List[Int]): Boolean = lst.exists(fn)

The exists function has the same semantics as what you're after - it returns true if fn returns true for at least one element, false otherwise.

Upvotes: 1

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