Scala Exists, forAll, takeWhile and simple fun with functions

funprog

type predicate[A] = A => Boolean

def exists[A](ls: List[A], p: A => Boolean): Boolean = {
  ls match {
    case x :: xs => p(x) || exists(xs,p)
    case _ => false
  }
}

def exists2[A](ls: List[A], p: predicate[A]): Boolean = {
  ls.foldRight(false)((a,z) => p(a) || z)
}

exists2(List(1,2,3,4),(x: Int) => x > 3)



def forAll[A](ls: List[A])( p: predicate[A]): Boolean = {
  ls.foldRight(true)((a, z) => p(a) && z)
}

forAll(List(1,2,3,4))(_>0)


def takeWhile[A](ls: List[A])(p: predicate[A]): List[A] = {
  ls.foldRight(List[A]())((a, z) =>
    if (p(a))  a :: z
    else z)
}

takeWhile(List(1,2,3,4,5))(_<4)