src/Pure/proof_general.ML

 in
   (* NB: simple tty for now; later might read from other tty-style sources (e.g. sockets). *)
 
   val xmlP = XML.scan_comment_whspc |-- XML.parse_elem >> single
 
-  val tty_src = Source.set_prompt "" (Source.source Symbol.stopper xmlP NONE Source.tty)
+  fun pgip_src istrm = Source.source Symbol.stopper xmlP NONE 
+			      (Source.of_instream_slurp istrm);
+
+  val tty_src = pgip_src TextIO.stdIn;
 
   fun pgip_toplevel x = loop true x
 end