part 2 of the dependent method refactoring: imp...

part 2 of the dependent method refactoring: improved interaction with
implicit search (needed for oopsla paper)

more to come in this area, see e.g. #3346 (stanford edsl stuff)

reopens #13, which wasn't fixed properly before imo, anyway (have a look at -Xprint:typer output before this commit: a type that's not expressible in surface syntax is inferred -- also removed duplicate test file)

closes #3731: co-evolve type alias type symbols when their rhs is
updated and they are referenced by type selections (see typemap)

review by odersky

1 files changed, 87 insertions, 0 deletions

diff --git a/test/files/pos/depmet_implicit_oopsla_session_2.scala b/test/files/pos/depmet_implicit_oopsla_session_2.scala
new file mode 100644
index 0000000000..5c3b78e3f5
--- /dev/null
+++ b/test/files/pos/depmet_implicit_oopsla_session_2.scala
@@ -0,0 +1,87 @@
+object Sessions {
+  def ?[T <: AnyRef](implicit w: T): w.type = w
+
+  // session states
+  sealed case class Stop()
+  sealed case class In[-Data, +Cont](recv: Data => Cont)
+  sealed case class Out[+Data, +Cont](data: Data, cont: Cont)
+
+  // the type theory of communicating sessions:
+
+  // an instance of type Session[S]{type Dual=D} is evidence that S and D are duals
+  // such a value witnesses this fact by describing how to compose an instance of S with an instance of D (through the run method)
+  trait Session[S] { type Self = S
+    type Dual
+    type HasDual[D] = Session[Self]{type Dual=D}
+    def run(self: Self, dual: Dual): Unit
+  }
+
+  // friendly interface to the theory
+  def runSession[S, D: Session[S]#HasDual](session: S, dual: D) =
+    ?[Session[S]#HasDual[D]].run(session, dual)
+
+  // facts in the theory:
+
+  // ------------------------[StopDual]
+  // Stop is the dual of Stop
+  implicit object StopDual extends Session[Stop] {
+    type Dual = Stop
+
+    def run(self: Self, dual: Dual): Unit = {}
+  }
+
+  //            CD is the dual of Cont
+  // -------------------------------------------[InDual]
+  // Out[Data, CD] is the dual of In[Data, Cont]
+  implicit def InDual[Data, Cont](implicit cont: Session[Cont]) = new Session[In[Data, Cont]] {
+    type Dual = Out[Data, cont.Dual]
+
+    def run(self: Self, dual: Dual): Unit =
+      cont.run(self.recv(dual.data), dual.cont)
+  }
+
+  //            CD is the dual of Cont
+  // -------------------------------------------[OutDual]
+  // In[Data, CD] is the dual of Out[Data, Cont]
+  implicit def OutDual[Data, Cont](implicit cont: Session[Cont]) = new Session[Out[Data, Cont]] {
+    type Dual = In[Data, cont.Dual]
+
+    def run(self: Self, dual: Dual): Unit =
+      cont.run(self.cont, dual.recv(self.data))
+  }
+
+  // a concrete session
+  def addServer =
+    In{x: Int =>
+    In{y: Int => System.out.println("Thinking")
+    Out(x+y,
+    Stop())}}
+
+  def addClient =
+    Out(3,
+    Out(4, { System.out.println("Waiting")
+    In{z: Int => System.out.println(z)
+    Stop()}}))
+
+  def myRun = runSession(addServer, addClient)
+}
+
+/* future improvements:
+
+
+  // def runSession[S, D](p: S, dp: D)(implicit s: Session[S]#HasDual[D]) =
+  //   s.run(p, dp)
+  //
+  // def runSession[S, D](p: S, dp: D)(implicit s: Session[S]{type Dual=D}) =
+  //   s.run(p, dp)
+
+  // TODO: can we relax the ordering restrictions on dependencies so that we can write
+  //  one possibility: graph of dependencies between arguments must be acyclic
+  // def runSession[S](p: S, dp: s.Dual)(implicit s: Session[S]) =
+  //   s.run(p, dp)
+  // to emphasise similarity of type parameters and implicit arguments:
+  // def runSession[S][val s: Session[S]](p: S, dp: s.Dual) =
+  //   s.run(p, dp)
+
+
+*/
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