Scala By Example Chapter 9 Solutions - Unnamed Exercise after 9.4.1

Exercise: Define forall and exists in terms of filter.

As before, since class List cannot be extended in scala, the methods are implemented as pure functions taking a list parameter.

	object ListFilter {
	def forall(xs: List[Int], p: Int => Boolean): Boolean =
	xs.isEmpty || xs.filter(p) == xs
	def exists(xs: List[Int], p: Int => Boolean): Boolean =
	!xs.isEmpty && !xs.filter(p).isEmpty
	def main(args: Array[String]) {
	println("Are members of list (1,2,3,4,5) less than 10? : " +
	forall(List(1,2,3,4,5), (x => x < 10)));
	println("Is there at least one member of list (1,2,3,4,5) thats greater than 5? : " +
	exists(List(1,2,3,4,5), (x => x > 5)));
	}
	}

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