Exercise from FP in Scala

Monoid.scala

	// EXERCISE 9: Implement a foldMap for IndexedSeq, a common supertype
	// for various data structures that provide efficient random access including Vector.
	// Your implementation should use the strategy of splitting the sequence in two,/
	// recursively processing each half, and then adding the answers together with the
	// monoid.
	def foldMapV[A,B](v: IndexedSeq[A], m: Monoid[B])(f: A => B): B = {
		def go(seq: List[B], acc: B): B = seq match {
			case x :: xs => go(xs, m.op(acc, x))
			case Nil => acc
		}

		val as: List[B] = v.map(f).toList
		val (a: List[B], b: List[B]) = as.splitAt(as.length / 2)
		m.op(go(a, m.zero), go(b, m.zero))
	}

testing:
val seq = IndexedSeq("1","2","3","4")
val r = foldMapV(seq, intAddition)(x => x.toInt)
println(r)
assert(r == 10)