Created
March 14, 2017 22:33
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| import cats.{ Applicative, Eval, Foldable, Monoid }, cats.implicits._ | |
| def foldMapM[F[_]: Foldable, G[_]: Applicative, A, B: Monoid](fa: F[A])(f: A => G[B]): G[B] = | |
| fa.foldRight(Eval.always(Monoid[B].empty.pure[G]))((a, acc) => f(a).map2Eval(acc)(_ |+| _)).value | |
| def sumIfSmall(s: Stream[Int]) = foldMapM(s) { | |
| case n if n < 100 => Right(n) | |
| case n => Left(n) | |
| } | |
| sumIfSmall(Stream.from(0)) // Left(100) |
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newb question: Left and Right are from?