Add pos test for structural pdgadt

Author: Linyxus

tests/pos/structural-pdt-pdgadt.scala

@@ -0,0 +1,13 @@
+type typed[E <: Expr, V] = E & { type T = V }
+
+trait Expr { type T }
+case class LitInt(x: Int) extends Expr { type T >: Int }
+case class Add(e1: Expr typed Int, e2: Expr typed Int) extends Expr { type T >: Int }
+case class LitBool(x: Boolean) extends Expr { type T >: Boolean }
+case class Or(e1: Expr typed Boolean, e2: Expr typed Boolean) extends Expr { type T >: Boolean }
+
+def eval(e: Expr): e.T = e match
+  case LitInt(x) => x
+  case Add(e1, e2) => eval(e1) + eval(e2)
+  case LitBool(b) => b
+  case Or(e1, e2) => eval(e1) || eval(e2)