Scala Map call multiple functions

Question

I am learning Scala and am a beginner. My trainer has given me some work, see below:

Let's construct a bouquet of functions that would test the following conditions on a given no "n". A) check prime. B) check if square. C) check irrational. Construct the bouquet as a Map[Char, Int=>Boolean]. Now accept the integer and code in {A, B,C} from the command line to call the appropriate function and print the result.

I write all program A, B and C. But using Map I don't know what to do.

object firstProgram
{
  def main(args: Array[String]):Unit =
   {
     square(9);
     primeNumber(19);
   }
  def square(x: Int): Unit =
  {
    var no = math.sqrt(x);
    if((no%1) == 0)
      println(x +" IS A SQUARE NUMBER OF - "+no.toInt);
    else
      println(x +" IS NOT A SQUARE NUMBER");
  }

  def primeNumber(x: Int) : Unit =
  {
      var a =0;
      var returnValue = false;
      for(a <- 2 until x)
      {
          if( (x%a) ==0)
            returnValue = true;
      }
    if(returnValue == false)
      println(x + " IS A PRIME NUMBER");
    else
      println(x + " IS NOT A PRIME NUMBER");
  }
}

How can I understand the question, and how to do it with Map?

The idea is that you store all the checks on a Map so the program will receive as input the number to check and the check to do (as a single letter), and you would extract the check from the map. - Anyways, I am pretty sure your trainee won't be happy that you solve this using mutability, and your checks are not checks, since they do not return a Boolean but instead print a value. — Luis Miguel Mejía Suárez
– Luis Miguel Mejía Suárez, Commented May 21, 2020 at 14:57
I don't see why there is a predicate to check if an Int is irrational. There's no way plain integers can be anything but rational — user
– user, Commented May 21, 2020 at 15:23

user · Accepted Answer · 2020-05-21 15:40:14Z

Since your map has keys that are characters and values that are predicates, I think your trainer wants you to have the letters 'A', 'B', and 'C' corresponding to isPerfectSquare, isPrime, isIrrational, etc. You can do that as such:

val checksMap = Map(
  'A' -> isPerfectSquare _,
  'B' -> isPrime _,
  'C' -> isIrrational _
)

Of course, for this to work, you'd have to change the signatures of your methods to look like

def isPerfectSquare(x: Int): Boolean
def isPrime(x: Int): Boolean
def isIrrational(x: Int): Boolean

Afterwards, you can read integers from the command line and iterate through the map, and if a check doesn't pass, you're probably supposed to print something like s"Check $key didn't pass"

for ((k, v) <- checksMap) if (!v(n)) println(s"Check $k not passed")

And may I suggest a cooler implementation of isPrime that I found online?

lazy val primes: LazyList[Int] = 3 #:: (LazyList.from(5, 2).filter(x => !primes.takeWhile(math.pow(_,2) < x).exists(x % _ == 0)))

def isPrime(x: Int): Boolean = x == 2 || primes.takeWhile(_ <= x).last == x

Link to Scastie (fill in the blanks): https://scastie.scala-lang.org/WRw8Z6FxSauBvxQ9PChbPA

Collectives™ on Stack Overflow

Scala Map call multiple functions

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related