added undo operation

Author: kr-2003

src/xinterpreter.cpp

@@ -134,14 +134,17 @@ __get_cxx_version ()
 
         auto input_guard = input_redirection(config.allow_stdin);
 
-        // Check for magics
-        for (auto& pre : preamble_manager.preamble)
+        if (code.find("%undo") != 0)
         {
-            if (pre.second.is_match(code))
+            // Check for magics
+            for (auto& pre : preamble_manager.preamble)
             {
-                pre.second.apply(code, kernel_res);
-                cb(kernel_res);
-                return;
+                if (pre.second.is_match(code))
+                {
+                    pre.second.apply(code, kernel_res);
+                    cb(kernel_res);
+                    return;
+                }
             }
         }
 
@@ -169,7 +172,32 @@ __get_cxx_version ()
         try
         {
             StreamRedirectRAII R(err);
-            compilation_result = Cpp::Process(code.c_str());
+            if (code.rfind("%undo", 0) == 0)
+            {
+                int n = 1;  // Default value
+                if (code.length() > 5)
+                {
+                    try
+                    {
+                        n = std::stoi(code.substr(6));
+                    }
+                    catch (const std::invalid_argument&)
+                    {
+                        throw std::runtime_error(
+                            "Invalid format for %undo. Expected '%undo n' where n is an integer."
+                        );
+                    }
+                    catch (const std::out_of_range&)
+                    {
+                        throw std::runtime_error("Number out of range for %undo.");
+                    }
+                }
+                compilation_result = Cpp::Undo(n) ? true : false;
+            }
+            else
+            {
+                compilation_result = Cpp::Process(code.c_str());
+            }
         }
         catch (std::exception& e)
         {