diff -r a5d1d1e2f109 -r 22b5ecb53dd9 src/Pure/Tools/print_operation.ML
--- a/src/Pure/Tools/print_operation.ML	Sun Apr 11 21:32:09 2021 +0200
+++ b/src/Pure/Tools/print_operation.ML	Sun Apr 11 22:47:55 2021 +0200
@@ -23,9 +23,9 @@
 
 fun report () =
   Output.try_protocol_message Markup.print_operations
-    (Synchronized.value print_operations
+    [Synchronized.value print_operations
       |> map (fn (x, (y, _)) => (x, y)) |> rev
-      |> let open XML.Encode in list (pair string string) end);
+      |> let open XML.Encode in list (pair string string) end];
 
 val _ = Protocol_Command.define "print_operations" (fn [] => report ());