src/Pure/PIDE/protocol_handlers.scala

       "Failed to initialize protocol handler: " + quote(name) + "\n" + Exn.message(exn))
 
   sealed case class State(
     session: Session,
     handlers: Map[String, Session.Protocol_Handler] = Map.empty,
-    functions: Map[String, Prover.Protocol_Output => Boolean] = Map.empty)
+    functions: Map[String, Session.Protocol_Function] = Map.empty)
   {
     def get(name: String): Option[Session.Protocol_Handler] = handlers.get(name)
 
     def init(handler: Session.Protocol_Handler): State =
     {