Show execution count on header line

lisp/ein-notification.el

@@ -55,6 +55,9 @@
 (defclass ein:notification ()
   ((buffer :initarg :buffer :type buffer :document "Notebook buffer")
    (tab :initarg :tab :type ein:notification-tab)
+   (execution-count
+    :initform "y" :initarg :execution-count
+    :documentation "Last `execution_count' sent by `execute_reply'.")
    (notebook
     :initarg :notebook
     :initform
@@ -103,6 +106,10 @@ where NS is `:kernel' or `:notebook' slot of NOTIFICATION."
                        "Notebook is saved"
                        'notebook_saved.Notebook
                        nil))
+  (ein:events-on events
+                 'execution_count.Kernel
+                 #'ein:notification--set-execution-count
+                 notification)
   (ein:events-on events
                  'status_restarting.Kernel
                  #'ein:notification--fadeout-callback
@@ -116,6 +123,9 @@ where NS is `:kernel' or `:notebook' slot of NOTIFICATION."
         (status (cdr packed)))
     (ein:notification-status-set ns status)))
 
+(defun ein:notification--set-execution-count (notification count)
+  (oset notification :execution-count count))
+
 (defun ein:notification--fadeout-callback (packed data)
   ;; FIXME: I can simplify this.
   ;;        Do not pass around message, for exmaple.
@@ -193,7 +203,8 @@ worksheet given as its argument."
 
 (defun ein:header-line ()
   (format
-   "IP[y]: %s"
+   "IP[%s]: %s"
+   (oref ein:%notification% :execution-count)
    (ein:join-str
     " | "
     (ein:filter