Merge pull request #2045 from dotty-staging/fix-hlist-hmap

Fix type inference for HLists and HMaps

1 files changed, 45 insertions, 0 deletions

diff --git a/tests/disabled/pos/depmet_implicit_oopsla_session_simpler.scala b/tests/disabled/pos/depmet_implicit_oopsla_session_simpler.scala
new file mode 100644
index 000000000..8cc6fe754
--- /dev/null
+++ b/tests/disabled/pos/depmet_implicit_oopsla_session_simpler.scala
@@ -0,0 +1,45 @@
+// Disabled because we now get an unsafe instantiation error
+object Sessions {
+  trait Session {
+    type Dual <: Session
+
+    def run(dp: Dual): Unit
+  }
+
+  sealed case class Stop() extends Session {
+    type Dual = Stop
+
+    def run(dp: Dual): Unit = {}
+  }
+
+  // can't write B <: Session{type Dual = BDual} due to limitations in type inference algorithm
+  // (type variables cannot occur on both sides of <:)
+  // using B#Dual instead of BDual is too imprecise, since it is disconnected from the actual argument that is passed for B
+  // would be nice if we could introduce a universal quantification over BDual that is not part of the
+  // type parameter list
+  sealed case class In[A, B <: Session, BDual <: Session](recv: A => B)(implicit dual: B <:< Session{type Dual=BDual}) extends Session {
+    type Dual = Out[A, BDual]
+
+    def run(dp: Dual): Unit = recv(dp.data) run dp.cont
+  }
+
+  sealed case class Out[A, B <: Session](data: A, cont: B) extends Session {
+     type Dual = In[A, cont.Dual, cont.Dual#Dual]
+
+     def run(dp: Dual): Unit = cont run dp.recv(data)
+  }
+
+  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 = addServer run addClient // error: unsafe instantiation
+}