__PACKAGE__() as a sub, not a special token

src/main/scala/org/moe/runtime/builtins/CorePackage.scala

@@ -229,5 +229,22 @@ object CorePackage {
         }
       )
     )
+
+    pkg.addSubroutine(
+      new MoeSubroutine(
+        "__PACKAGE__",
+        new MoeSignature(),
+        env,
+        { (e) =>
+          val caller_env = r.getInterpreterCallStack.head.getCallSiteEnvironment
+          val caller_pkg = caller_env.getCurrentPackage match {
+            case Some(x) => x.getFullyQualifiedName
+            case None    => ""
+            case _       => ""
+          }
+          getStr(caller_pkg)
+        }
+      )
+    )
   }
 }

t/100-builtins/008-package.t

@@ -0,0 +1,9 @@
+use Test::More;
+
+package Bar {
+    sub quux { __PACKAGE__() }
+}
+
+is(Bar::quux(), "Bar", '__PACKAGE__ returns what we expect');
+
+done_testing();