gracefully ignore invalid input

main.ml

@@ -54,6 +54,7 @@ let rec interactive ((g, gs) : proof) : proof =
     | Some g' -> print_goal g'
     in
 
+    try
       match parse_cmd (Lexing.from_string ((read_line ())^"\n")) with
       Goal ty -> fresh_proof ty |> interactive
       | Tact t ->
@@ -71,6 +72,13 @@ let rec interactive ((g, gs) : proof) : proof =
           | Apply id ->
             tact_apply (g, gs) id |> interactive
         end
+    with
+      Parser.Error ->
+        print_string "Invalid input.\n";
+        interactive (g, gs)
+      | End_of_file ->
+        print_string "Bye!\n";
+        (g, gs)
   end
 
 let interpret e =