Example code for the Singapore scala meetup

Meetup.scala

import scala.annotation.tailrec

def sum(nums: Seq[Int]) = fold(0)(nums, _ + _)

def filterEven(nums: Seq[Int]): Seq[Int] = filter(nums, _ % 2 == 0)

def filter(nums: Seq[Int], predicate: Int => Boolean): Seq[Int] =
  fold(List[Int]())(nums, (l, i) => if (predicate(i)) l :+ i else l)

def square(nums: Seq[Int]): Seq[Int] = map(nums, i => i * i)

def map(nums: Seq[Int], f: Int => Int): Seq[Int] =
  fold(List[Int]())(nums, _ :+ f(_))

def fold[B](zero: B)(seq: Seq[Int], f: (B, Int) => B): B = {
  var result = zero
  for (i <- seq) {
    result = f(result, i)
  }
  result
}

@tailrec
def foldRec[A, B](zero: B)(
  seq: Seq[A],
  f: (B, A) => B): B = {

  if (seq.isEmpty) zero
  else foldRec(f(zero, seq.head))(seq.tail, f)
}

val nums = 1 to 10
val evens = filterEven(nums)
val squares = square(evens)
val result = sum(squares)

println(s"Sum is $result")

def isEven: Int => Boolean = _ % 2 == 0
val result2 = nums.filter(isEven).map(i => i * i).sum