tuned message;

--- a/src/Pure/Thy/sessions.scala	Fri Mar 17 10:58:32 2017 +0100
+++ b/src/Pure/Thy/sessions.scala	Fri Mar 17 11:15:57 2017 +0100
@@ -606,6 +606,11 @@
       find_heap(name) getOrElse
         error("Unknown logic " + quote(name) + " -- no heap file found in:\n" +
           cat_lines(input_dirs.map(dir => "  " + dir.expand.implode)))
+
+
+    /* print */
+
+    override def toString: String = "Store(output_dir = " + output_dir.expand + ")"
   }