[vpm] __match determines match semantics; virtualization

determine match strategy by typing `__match`
factored out the interface to generate code in this monad, cleaned up codegen a bit

no longer solving a context bound to determine the match strategy and the monad's type constructor
it's too expensive

don't consider implicits looking for __match
implicit search causes HUGE slowdowns -- now the overhead is about 4% compared to just assuming there's no __match in scope

to support virtualization&staging, we use the type of `__match.one` as the prototype for how to wrap "pure" types and types "in the monad"
pure types T are wrapped as P[T], and T goes into the monad as M[T], if one is defined as:

  def one[T](x: P[T]): M[T]

for staging, P will typically be the Rep type constructor, and type M[T] = Rep[Option[T]]

furthermore, naive codegen no longer supplies type information -- type inference will have to work it out
optimized codegen still does, of course, and that's enough since we only bootstrap that way

TODO: improve the test (currently the condition is not represented)

1 files changed, 52 insertions, 0 deletions

diff --git a/test/files/run/virtpatmat_staging.scala b/test/files/run/virtpatmat_staging.scala
new file mode 100644
index 0000000000..c17b45043b
--- /dev/null
+++ b/test/files/run/virtpatmat_staging.scala
@@ -0,0 +1,52 @@
+trait Intf {
+ type Rep[+T]
+ type M[+T] = Rep[Maybe[T]]
+
+ val __match: Matcher
+ abstract class Matcher {
+   // runs the matcher on the given input
+   def runOrElse[T, U](in: Rep[T])(matcher: Rep[T] => M[U]): Rep[U]
+
+   def zero: M[Nothing]
+   def one[T](x: Rep[T]): M[T]
+   def guard[T](cond: Rep[Boolean], then: => Rep[T]): M[T]
+   def isSuccess[T, U](x: Rep[T])(f: Rep[T] => M[U]): Rep[Boolean] // used for isDefinedAt
+ }
+
+ abstract class Maybe[+A] {
+   def flatMap[B](f: Rep[A] => M[B]): M[B]
+   def orElse[B >: A](alternative: => M[B]): M[B]
+ }
+
+ implicit def proxyMaybe[A](m: M[A]): Maybe[A]
+ implicit def repInt(x: Int): Rep[Int]
+ implicit def repBoolean(x: Boolean): Rep[Boolean]
+ implicit def repString(x: String): Rep[String]
+
+ def test = 7 match { case 5 => "foo" case _ => "bar" }
+}
+
+trait Impl extends Intf {
+ type Rep[+T] = String
+
+ object __match extends Matcher {
+   def runOrElse[T, U](in: Rep[T])(matcher: Rep[T] => M[U]): Rep[U] = ("runOrElse("+ in +", ?" + matcher("?") + ")")
+   def zero: M[Nothing]                                             = "zero"
+   def one[T](x: Rep[T]): M[T]                                      = "one("+x.toString+")"
+   def guard[T](cond: Rep[Boolean], then: => Rep[T]): M[T]          = "guard("+cond+","+then+")"
+   def isSuccess[T, U](x: Rep[T])(f: Rep[T] => M[U]): Rep[Boolean]  = ("isSuccess("+x+", ?" + f("?") + ")")
+ }
+
+ implicit def proxyMaybe[A](m: M[A]): Maybe[A] = new Maybe[A] {
+   def flatMap[B](f: Rep[A] => M[B]): M[B]                          = m + ".flatMap(? =>"+ f("?") +")"
+   def orElse[B >: A](alternative: => M[B]): M[B]                   = m + ".orElse("+ alternative +")"
+ }
+
+ def repInt(x: Int): Rep[Int] = x.toString
+ def repBoolean(x: Boolean): Rep[Boolean] = x.toString
+ def repString(x: String): Rep[String] = x
+}
+
+object Test extends Impl with Intf with App {
+  println(test)
+}