src/Pure/General/name_space.ML

           val reports =
             filter (Context_Position.is_reported_generic context) ps
             |> map (fn pos => (pos, markup space name));
         in ((name, reports), x) end
     | NONE =>
-        let
-          val completions = map (fn pos => completion context space (K true) (xname, pos)) ps;
-        in
-          error (undefined space name ^ Position.here_list ps ^
-            Markup.markup_report (implode (map Completion.reported_text completions)))
-        end)
+        error (undefined space name ^ Position.here_list ps ^
+          Completion.markup_report
+            (map (fn pos => completion context space (K true) (xname, pos)) ps)))
   end;
 
 fun check context table (xname, pos) =
   let
     val ((name, reports), x) = check_reports context table (xname, [pos]);