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@cvogt
Created March 23, 2014 00:24
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trait Monoid[M] {
def zero: M
def add(m1: M, m2: M): M
}
trait Foldable[F[_]] {
def foldl[A, B](as: F[A], z: B, f: (B, A) => B): B
}
def mapReduce[F[_], A, B](as: F[A], m: Monoid[A])
(implicit ff: Foldable[F]) =
ff.foldl(as, m.zero, m.add)
val sum = new Monoid[Int] {
def zero = 0
def add(a: Int, b: Int) = a + b
}
val product = new Monoid[Int] {
def zero = 1
def add(a: Int, b: Int) = a * b
}
implicit val listFoldable = new Foldable[List] {
def foldl[A, B](as: List[A], z: B, f: (B, A) => B) = as.foldLeft(z)(f)
}
val sumOf123 = mapReduce(List(1,2,3), sum)
val productOf456 = mapReduce(List(4,5,6), product)
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