Create a definition of the Split[T, N] type

Author: Antoine Brunner

library/src/scala/Tuple.scala

@@ -65,7 +65,7 @@ object Tuple {
   }
 
   /** Type of the concatenation of two tuples */
-  type Concat[X <: Tuple, +Y <: Tuple] <: Tuple = X match {
+  type Concat[+X <: Tuple, +Y <: Tuple] <: Tuple = X match {
     case Unit => Y
     case x1 *: xs1 => x1 *: Concat[xs1, Y]
   }
@@ -116,6 +116,29 @@ object Tuple {
    */
   type IsMappedBy[F[_]] = [X <: Tuple] =>> X =:= Map[InverseMap[X, F], F]
 
+  /** Transforms a tuple `(T1, ..., Tn)` into `(T1, ..., Ti)`. */
+  type Take[+T <: Tuple, N <: Int] = N match {
+    case 0 => Unit
+    case S[n1] => T match {
+      case Unit => Unit
+      case x *: xs => Concat[x *: Unit, Take[xs, n1]]
+    }
+  }
+
+  /** Transforms a tuple `(T1, ..., Tn)` into `(Ti+1, ..., Tn)`. */
+  type Drop[+T <: Tuple, N <: Int] = N match {
+    case 0 => T
+    case S[n1] => T match {
+      case Unit => Unit
+      case x *: xs => Drop[xs, n1]
+    }
+  }
+
+  /** Splits a tuple (T1, ..., Tn) into a pair of two tuples `(T1, ..., Ti)` and
+   * `(Ti+1, ..., Tn)`.
+   */
+  type Split[+T <: Tuple, N <: Int] = (Take[T, N], Drop[T, N]) = (Take[T, N], Drop[T, N])
+
   /** Convert an array into a tuple of unknown arity and types */
   def fromArray[T](xs: Array[T]): Tuple = {
     val xs2 = xs match {