diff --git a/Dockerfile b/Dockerfile
index cb01866..6b9c665 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,7 +1,6 @@
 # syntax=docker/dockerfile:1.4
 ARG BASE_IMAGE=ubuntu:noble
 FROM ${BASE_IMAGE}
-WORKDIR /autograder
 WORKDIR /opt/SYsU-lang
 COPY <<build_install.sh <<run.sh . /opt/SYsU-lang
 #!/bin/sh
@@ -27,7 +26,6 @@ rm -rf /opt/SYsU-lang/optimizer
 cp -r /opt/SYsU-lang/submission/*-Source/optimizer /opt/SYsU-lang
 rm -rf /opt/SYsU-lang/submission
 /opt/SYsU-lang/build_install.sh /opt/SYsU-lang /opt/sysu
-mkdir -p /autograder/results
 sysu-compiler \\
     --unittest=benchmark_generator_and_optimizer_1 \\
     "/opt/SYsU-lang/**/*.sysu.c" >/autograder/results/results.json
@@ -41,6 +39,7 @@ apt-get install -y --no-install-recommends \
 apt-get autoremove -y
 apt-get clean -y
 rm -rf /var/lib/apt/lists/*
+mkdir -p /autograder/results
 mv /opt/SYsU-lang/run.sh /autograder/run
 chmod +x /autograder/run
 chmod +x /opt/SYsU-lang/build_install.sh
diff --git a/grammar/README.md b/grammar/README.md
index 8c75bcf..d251d56 100644
--- a/grammar/README.md
+++ b/grammar/README.md
@@ -274,6 +274,12 @@ flowchart TD;
 2. 输出到 json，因为 json 格式非常容易理解，不需要像 [LLVM 官方教程](https://releases.llvm.org/17.0.0/docs/tutorial/MyFirstLanguageFrontend/LangImpl02.html) 一样定义很多节点。
 3. 输出到 `llvm::json`，可以让同学们提前上手 LLVM 库的使用，平滑下一个实验的难度。
 
+### Q & A：该选择 Visitor 还是 Listener？
+
+TL;DR: Vistor 更符合任务需求，但是 Listener 仍然更加趁手。
+
+Visitor 有更强的可定制性，但是需要自行实现每个节点到子节点的访问规则；Listener 则适合更轻量的任务，例如只提取某些语法规则的上下文。在本实验中，按道理每个节点都需要被访问，因此 Vistor 更符合任务需求，Listener 的优势没有那么大。然而，根据助教的使用经验，Listener 仍然是一个更常用且好用的选择。
+
 ## 评分规则
 
 本实验的评分分为两部分：基础部分和挑战部分。
diff --git a/grammar/main.cc b/grammar/main.cc
index 31dfeb9..c9b59b1 100644
--- a/grammar/main.cc
+++ b/grammar/main.cc
@@ -6,6 +6,7 @@
 #include "CVisitor.h"
 #include <algorithm>
 #include <antlr4-runtime.h>
+#include <any>
 #include <llvm/Support/JSON.h>
 #include <llvm/Support/MemoryBuffer.h>
 #include <llvm/Support/raw_ostream.h>
@@ -48,27 +49,28 @@ int main(int argc, char **argv) {
     return 0;
   }
   sysu_grammar::CParser parser(&tokens);
-#ifndef SYSU_GRAMMAR_USE_LISTENER // 任 君 选 择
-  struct Visitor : sysu_grammar::CBaseVisitor {
-    antlrcpp::Any visitCompilationUnit(
-        sysu_grammar::CParser::CompilationUnitContext *ctx) override {
-      return visit(ctx->translationUnit());
-    }
-    antlrcpp::Any visitTranslationUnit(
+#ifndef SYSU_GRAMMAR_NO_USE_LISTENER // 任 君 选 择
+  struct Listener : sysu_grammar::CBaseListener {
+    llvm::json::Array stak;
+    void exitTranslationUnit(
         sysu_grammar::CParser::TranslationUnitContext *ctx) override {
       llvm::json::Value ret = llvm::json::Object{
           {"kind", "TranslationUnitDecl"}, {"inner", llvm::json::Array{}}};
-      for (auto child : ctx->externalDeclaration()) {
-        ret.getAsObject()->get("inner")->getAsArray()->push_back(
-            visit(child).as<llvm::json::Value>());
+      ret.getAsObject()->get("inner")->getAsArray()->reserve(
+          ctx->externalDeclaration().size());
+      for (const auto &child : ctx->externalDeclaration()) {
+        ret.getAsObject()->get("inner")->getAsArray()->push_back(stak.back());
+        stak.pop_back();
       }
-      return ret;
+      std::reverse(ret.getAsObject()->get("inner")->getAsArray()->begin(),
+                   ret.getAsObject()->get("inner")->getAsArray()->end());
+      stak.push_back(ret);
     }
-    // 请续写 visitExternalDeclaration 及之后的遍历逻辑，将 ParseTree 转换为
+    // 请续写 exitExternalDeclaration 及之后的遍历逻辑，将 ParseTree 转换为
     // json 格式的 AbstractSyntaxTree，简而言之就是把树拍扁
-    antlrcpp::Any visitExternalDeclaration(
+    void exitExternalDeclaration(
         sysu_grammar::CParser::ExternalDeclarationContext *ctx) override {
-      return llvm::json::Value(llvm::json::Object{
+      stak.push_back(llvm::json::Object{
           {"kind", "FunctionDecl"},
           {"name", "main"},
           {"inner",
@@ -82,32 +84,31 @@ int main(int argc, char **argv) {
                 }}},
            }}}});
     }
-  };
-  llvm::outs()
-      << Visitor().visit(parser.compilationUnit()).as<llvm::json::Value>()
-      << "\n";
+  } listener;
+  antlr4::tree::ParseTreeWalker::DEFAULT.walk(&listener,
+                                              parser.compilationUnit());
+  llvm::outs() << listener.stak.back() << "\n";
 #else
-  struct Listener : sysu_grammar::CBaseListener {
-    llvm::json::Array stak;
-    void exitTranslationUnit(
+  struct Visitor : sysu_grammar::CBaseVisitor {
+    antlrcpp::Any visitCompilationUnit(
+        sysu_grammar::CParser::CompilationUnitContext *ctx) override {
+      return visit(ctx->translationUnit());
+    }
+    antlrcpp::Any visitTranslationUnit(
         sysu_grammar::CParser::TranslationUnitContext *ctx) override {
       llvm::json::Value ret = llvm::json::Object{
           {"kind", "TranslationUnitDecl"}, {"inner", llvm::json::Array{}}};
-      ret.getAsObject()->get("inner")->getAsArray()->reserve(
-          ctx->externalDeclaration().size());
-      for (const auto &child : ctx->externalDeclaration()) {
-        ret.getAsObject()->get("inner")->getAsArray()->push_back(stak.back());
-        stak.pop_back();
+      for (auto child : ctx->externalDeclaration()) {
+        ret.getAsObject()->get("inner")->getAsArray()->push_back(
+            std::any_cast<llvm::json::Value>(visit(child)));
       }
-      std::reverse(ret.getAsObject()->get("inner")->getAsArray()->begin(),
-                   ret.getAsObject()->get("inner")->getAsArray()->end());
-      stak.push_back(ret);
+      return ret;
     }
-    // 请续写 exitExternalDeclaration 及之后的遍历逻辑，将 ParseTree 转换为
+    // 请续写 visitExternalDeclaration 及之后的遍历逻辑，将 ParseTree 转换为
     // json 格式的 AbstractSyntaxTree，简而言之就是把树拍扁
-    void exitExternalDeclaration(
+    antlrcpp::Any visitExternalDeclaration(
         sysu_grammar::CParser::ExternalDeclarationContext *ctx) override {
-      stak.push_back(llvm::json::Object{
+      return llvm::json::Value(llvm::json::Object{
           {"kind", "FunctionDecl"},
           {"name", "main"},
           {"inner",
@@ -121,9 +122,9 @@ int main(int argc, char **argv) {
                 }}},
            }}}});
     }
-  } listener;
-  antlr4::tree::ParseTreeWalker::DEFAULT.walk(&listener,
-                                              parser.compilationUnit());
-  llvm::outs() << listener.stak.back() << "\n";
+  };
+  llvm::outs() << std::any_cast<llvm::json::Value>(
+                      Visitor().visit(parser.compilationUnit()))
+               << "\n";
 #endif
 }
\ No newline at end of file