gracefully ignore invalid input

main.ml

@@ -54,23 +54,31 @@ let rec interactive ((g, gs) : proof) : proof =
     | Some g' -> print_goal g'
     in
 
-    match parse_cmd (Lexing.from_string ((read_line ())^"\n")) with
-    Goal ty -> fresh_proof ty |> interactive
-    | Tact t ->
-      begin match t with
-        Exact_term e ->
-          tact_exact_term (g, gs) e |> interactive
-        | Exact_proof s ->
-            tact_exact_proof (g, gs) s |> interactive
-        | Assumption ->
-          tact_assumption (g, gs) |> interactive
-        | Intro ->
-          tact_intro (g, gs) |> interactive
-        | Cut ty ->
-          tact_cut (g, gs) ty |> interactive
-        | Apply id ->
-          tact_apply (g, gs) id |> interactive
-      end
+    try
+      match parse_cmd (Lexing.from_string ((read_line ())^"\n")) with
+      Goal ty -> fresh_proof ty |> interactive
+      | Tact t ->
+        begin match t with
+          Exact_term e ->
+            tact_exact_term (g, gs) e |> interactive
+          | Exact_proof s ->
+              tact_exact_proof (g, gs) s |> interactive
+          | Assumption ->
+            tact_assumption (g, gs) |> interactive
+          | Intro ->
+            tact_intro (g, gs) |> interactive
+          | Cut ty ->
+            tact_cut (g, gs) ty |> interactive
+          | 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 =