src/Pure/General/output.ML

--- a/src/Pure/General/output.ML	Wed Mar 26 20:08:07 2014 +0100
+++ b/src/Pure/General/output.ML	Wed Mar 26 20:32:15 2014 +0100
@@ -30,6 +30,8 @@
   val error_message: string -> unit
   val prompt: string -> unit
   val status: string -> unit
+  val direct_report: string -> unit
+  val redirect_report: (string -> unit) -> ('a -> 'b) -> 'a -> 'b
   val report: string -> unit
   val result: Properties.T -> string -> unit
   val protocol_message: Properties.T -> string -> unit
@@ -115,7 +117,17 @@
 fun error_message s = error_message' (serial (), s);
 fun prompt s = ! prompt_fn (output s);
 fun status s = ! status_fn (output s);
-fun report s = ! report_fn (output s);
+
+fun direct_report s = ! report_fn (output s);
+
+local
+  val tag = Universal.tag () : (string -> unit) Universal.tag;
+  fun thread_data () = the_default direct_report (Thread.getLocal tag);
+in
+  fun redirect_report rep = Library.setmp_thread_data tag (thread_data ()) rep;
+  fun report s = thread_data () s;
+end;
+
 fun result props s = ! result_fn props (output s);
 fun protocol_message props s = ! protocol_message_fn props (output s);
 fun try_protocol_message props s = protocol_message props s handle Protocol_Message _ => ();