From 9ba4cb69331386dfde9bac69dc2d5b22401face3 Mon Sep 17 00:00:00 2001
From: Li Haoyi <haoyi.sg@gmail.com>
Date: Wed, 12 Dec 2018 16:56:02 -0800
Subject: collapse boilerplate folder structure within src/ folders (#505)

* collapse boilerplate folder structure within src/ folders

* .
---
 main/core/src/util/EitherOps.scala | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)
 create mode 100644 main/core/src/util/EitherOps.scala

(limited to 'main/core/src/util/EitherOps.scala')

diff --git a/main/core/src/util/EitherOps.scala b/main/core/src/util/EitherOps.scala
new file mode 100644
index 00000000..da2552c8
--- /dev/null
+++ b/main/core/src/util/EitherOps.scala
@@ -0,0 +1,18 @@
+package mill.util
+
+import scala.collection.generic.CanBuildFrom
+import scala.collection.mutable
+import scala.language.higherKinds
+
+object EitherOps {
+
+  // implementation similar to scala.concurrent.Future#sequence
+  def sequence[A, B, M[X] <: TraversableOnce[X]](in: M[Either[A, B]])(
+      implicit cbf: CanBuildFrom[M[Either[A, B]], B, M[B]]): Either[A, M[B]] = {
+    in.foldLeft[Either[A, mutable.Builder[B, M[B]]]](Right(cbf(in))) {
+        case (acc, el) =>
+          for (a <- acc; e <- el) yield a += e
+      }
+      .map(_.result())
+  }
+}
-- 
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