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work around for 2.10. pattern matching on KNil now requires KNil()

This commit is contained in:
Mark Harrah 2012-03-17 19:31:03 -04:00
parent 0e130d29e9
commit 8fc5db4a8a
2 changed files with 14 additions and 12 deletions
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24
util/collection/KList.scala
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@ -13,7 +13,7 @@ import Types._
* For background, see
* http://apocalisp.wordpress.com/2010/11/01/type-level-programming-in-scala-part-8a-klist%C2%A0motivation/
*/
sealed trait KList[+M[_], HL <: HList]
sealed trait KList[M[_], HL <: HList]
{
type Raw = HL
/** Transform to the underlying HList type.*/
@ -33,12 +33,12 @@ trait KFold[M[_],P[_ <: HList]]
def knil: P[HNil]
}
final case class KCons[H, T <: HList, +M[_]](head: M[H], tail: KList[M,T]) extends KList[M, H :+: T]
final case class KCons[H, T <: HList, M[_]](head: M[H], tail: KList[M,T]) extends KList[M, H :+: T]
{
def down(implicit f: M ~> Id) = HCons(f(head), tail down f)
def transform[N[_]](f: M ~> N) = KCons( f(head), tail transform f )
// prepend
def :^: [N[X] >: M[X], G](g: N[G]) = KCons(g, this)
def :^: [G](g: M[G]) = KCons(g, this)
def toList = head :: tail.toList
def combine[N[X] >: M[X]]: (H :+: T)#Wrap[N] = HCons(head, tail.combine)
@ -48,29 +48,31 @@ final case class KCons[H, T <: HList, +M[_]](head: M[H], tail: KList[M,T]) exten
def foldr[P[_ <: HList],N[X] >: M[X]](f: KFold[N,P]) = f.kcons(head, tail foldr f)
}
sealed class KNil extends KList[Nothing, HNil]
sealed case class KNil[M[_]]() extends KList[M, HNil]
{
def down(implicit f: Nothing ~> Id) = HNil
def transform[N[_]](f: Nothing ~> N) = KNil
def :^: [M[_], H](h: M[H]) = KCons(h, this)
def down(implicit f: M ~> Id) = HNil
def transform[N[_]](f: M ~> N) = new KNil[N]
def toList = Nil
def combine[N[X]] = HNil
override def foldr[P[_ <: HList],N[_]](f: KFold[N,P]) = f.knil
override def toString = "KNil"
}
object KNil extends KNil
object KNil
{
def :^: [M[_], H](h: M[H]) = KCons(h, new KNil[M])
}
object KList
{
implicit def convert[M[_]](k: KNil.type): KNil[M] = KNil()
// nicer alias for pattern matching
val :^: = KCons
def fromList[M[_]](s: Seq[M[_]]): KList[M, _ <: HList] = if(s.isEmpty) KNil else KCons(s.head, fromList(s.tail))
def fromList[M[_]](s: Seq[M[_]]): KList[M, _ <: HList] = if(s.isEmpty) KNil() else KCons(s.head, fromList(s.tail))
// haven't found a way to convince scalac that KList[M, H :+: T] implies KCons[H,T,M]
// Therefore, this method exists to put the cast in one location.
implicit def kcons[H, T <: HList, M[_]](kl: KList[M, H :+: T]): KCons[H,T,M] =
kl.asInstanceOf[KCons[H,T,M]]
// haven't need this, but for symmetry with kcons:
implicit def knil[M[_]](kl: KList[M, HNil]): KNil = KNil
implicit def knil[M[_]](kl: KList[M, HNil]): KNil[M] = KNil()
}

2
util/collection/Types.scala
View File

@ -7,7 +7,7 @@ object Types extends Types
{
implicit def hconsToK[M[_], H, T <: HList](h: M[H] :+: T)(implicit mt: T => KList[M, T]): KList[M, H :+: T] =
KCons[H, T, M](h.head, mt(h.tail) )
implicit def hnilToK(hnil: HNil): KNil = KNil
implicit def hnilToK[M[_]](hnil: HNil): KNil[M] = KNil()
}
trait Types extends TypeFunctions