tuned output;

--- a/src/Pure/Thy/export.scala	Tue Aug 28 12:39:37 2018 +0200
+++ b/src/Pure/Thy/export.scala	Tue Aug 28 12:42:57 2018 +0200
@@ -203,18 +203,24 @@
       new Provider {
         def apply(export_name: String): Option[Entry] =
           read_entry(db, session_name, theory_name, export_name)
+
+        override def toString: String = db.toString
       }
 
     def snapshot(snapshot: Document.Snapshot): Provider =
       new Provider {
         def apply(export_name: String): Option[Entry] =
           snapshot.exports_map.get(export_name)
+
+        override def toString: String = snapshot.toString
       }
 
     def directory(dir: Path, session_name: String, theory_name: String): Provider =
       new Provider {
         def apply(export_name: String): Option[Entry] =
           read_entry(dir, session_name, theory_name, export_name)
+
+        override def toString: String = dir.toString
       }
   }