Created
March 4, 2012 21:01
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Collect
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| def toCollector[A, B, U](x: A, f: (A) ⇒ B, g: U ⇒ U) = State[B,U]((s: U) ⇒ (f(x), g(s))) | |
| def collect[A, B, T[_], U](source: T[A])(f: (A) ⇒ B, g: U ⇒ U)(implicit t: Traverse[T]): State[T[B], U] = { | |
| type Projection[X] = State[X, U] | |
| implicit val A = stateApplicative[U]() | |
| t.traverse[Projection, A, B](source)((x: A) ⇒ toCollector(x, f, g)) | |
| } | |
| println((collect(List(10, 20, 30, 40))((a: Int) ⇒ 2 * a, (i: Int) ⇒ i + 1)).apply(0)) | |
| //Produces (List(20, 40, 60, 80),4) |
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