diff --git a/cclox_src/parser/expr.cc b/cclox_src/parser/expr.cc
index f7a6482..057166d 100644
--- a/cclox_src/parser/expr.cc
+++ b/cclox_src/parser/expr.cc
@@ -11,21 +11,25 @@ Expr::Expr(const Expr &other) : type{other.type} {
   switch(type) {
     case ExprType::BINARY: {
       std::shared_ptr<_Binary> ptr = std::get<std::shared_ptr<_Binary>>(other.value);
+      assert(ptr != nullptr);
       value = std::make_shared<_Binary>(*ptr);
       break;
     }
     case ExprType::GROUPING: {
       std::shared_ptr<_Grouping> ptr = std::get<std::shared_ptr<_Grouping>>(other.value);
+      assert(ptr != nullptr);
       value = std::make_shared<_Grouping>(*ptr);
       break;
     }
     case ExprType::LITERAL: {
       std::shared_ptr<_Literal> ptr = std::get<std::shared_ptr<_Literal>>(other.value);
+      assert(ptr != nullptr);
       value = std::make_shared<_Literal>(*ptr);
       break;
     }
     case ExprType::UNARY: {
       std::shared_ptr<_Unary> ptr = std::get<std::shared_ptr<_Unary>>(other.value);
+      assert(ptr != nullptr);
       value = std::make_shared<_Unary>(*ptr);
       break;
     }
@@ -37,21 +41,25 @@ Expr::Expr(const Expr &&other) : type{other.type}, value{std::move(other.value)}
   switch(type) {
     case ExprType::BINARY: {
       std::shared_ptr<_Binary> ptr = std::get<std::shared_ptr<_Binary>>(other.value);
+      assert(ptr != nullptr);
       ptr.reset();
       break;
     }
     case ExprType::GROUPING: {
       std::shared_ptr<_Grouping> ptr = std::get<std::shared_ptr<_Grouping>>(other.value);
+      assert(ptr != nullptr);
       ptr.reset();
       break;
     }
     case ExprType::LITERAL: {
       std::shared_ptr<_Literal> ptr = std::get<std::shared_ptr<_Literal>>(other.value);
+      assert(ptr != nullptr);
       ptr.reset();
       break;
     }
     case ExprType::UNARY: {
       std::shared_ptr<_Unary> ptr = std::get<std::shared_ptr<_Unary>>(other.value);
+      assert(ptr != nullptr);
       ptr.reset();
       break;
     }
@@ -67,21 +75,25 @@ Expr &Expr::operator=(const Expr &other) {
   switch(type) {
     case ExprType::BINARY: {
       std::shared_ptr<_Binary> ptr = std::get<std::shared_ptr<_Binary>>(value);
+      assert(ptr != nullptr);
       ptr.reset();
       break;
     }
     case ExprType::GROUPING: {
       std::shared_ptr<_Grouping> ptr = std::get<std::shared_ptr<_Grouping>>(value);
+      assert(ptr != nullptr);
       ptr.reset();
       break;
     }
     case ExprType::LITERAL: {
       std::shared_ptr<_Literal> ptr = std::get<std::shared_ptr<_Literal>>(value);
+      assert(ptr != nullptr);
       ptr.reset();
       break;
     }
     case ExprType::UNARY: {
       std::shared_ptr<_Unary> ptr = std::get<std::shared_ptr<_Unary>>(value);
+      assert(ptr != nullptr);
       ptr.reset();
       break;
     }
@@ -92,21 +104,25 @@ Expr &Expr::operator=(const Expr &other) {
   switch(type) {
     case ExprType::BINARY: {
       std::shared_ptr<_Binary> ptr = std::get<std::shared_ptr<_Binary>>(other.value);
+      assert(ptr != nullptr);
       value = std::make_shared<_Binary>(*ptr);
       break;
     }
     case ExprType::GROUPING: {
       std::shared_ptr<_Grouping> ptr = std::get<std::shared_ptr<_Grouping>>(other.value);
+      assert(ptr != nullptr);
       value = std::make_shared<_Grouping>(*ptr);
       break;
     }
     case ExprType::LITERAL: {
       std::shared_ptr<_Literal> ptr = std::get<std::shared_ptr<_Literal>>(other.value);
+      assert(ptr != nullptr);
       value = std::make_shared<_Literal>(*ptr);
       break;
     }
     case ExprType::UNARY: {
       std::shared_ptr<_Unary> ptr = std::get<std::shared_ptr<_Unary>>(other.value);
+      assert(ptr != nullptr);
       value = std::make_shared<_Unary>(*ptr);
       break;
     }
@@ -124,21 +140,25 @@ Expr &Expr::operator=(const Expr &&other) {
   switch(type) {
     case ExprType::BINARY: {
       std::shared_ptr<_Binary> ptr = std::get<std::shared_ptr<_Binary>>(value);
+      assert(ptr != nullptr);
       ptr.reset();
       break;
     }
     case ExprType::GROUPING: {
       std::shared_ptr<_Grouping> ptr = std::get<std::shared_ptr<_Grouping>>(value);
+      assert(ptr != nullptr);
       ptr.reset();
       break;
     }
     case ExprType::LITERAL: {
       std::shared_ptr<_Literal> ptr = std::get<std::shared_ptr<_Literal>>(value);
+      assert(ptr != nullptr);
       ptr.reset();
       break;
     }
     case ExprType::UNARY: {
       std::shared_ptr<_Unary> ptr = std::get<std::shared_ptr<_Unary>>(value);
+      assert(ptr != nullptr);
       ptr.reset();
       break;
     }
@@ -148,27 +168,31 @@ Expr &Expr::operator=(const Expr &&other) {
 
   switch(type) {
     case ExprType::BINARY: {
-      std::shared_ptr<_Binary> optr = std::get<std::shared_ptr<_Binary>>(other.value);
+      std::shared_ptr<_Binary> ptr = std::get<std::shared_ptr<_Binary>>(other.value);
+      assert(ptr != nullptr);
       value = std::move(other.value);
-      optr.reset();
+      ptr.reset();
       break;
     }
     case ExprType::GROUPING: {
-      std::shared_ptr<_Grouping> optr = std::get<std::shared_ptr<_Grouping>>(other.value);
+      std::shared_ptr<_Grouping> ptr = std::get<std::shared_ptr<_Grouping>>(other.value);
+      assert(ptr != nullptr);
       value = std::move(other.value);
-      optr.reset();
+      ptr.reset();
       break;
     }
     case ExprType::LITERAL: {
-      std::shared_ptr<_Literal> optr = std::get<std::shared_ptr<_Literal>>(other.value);
+      std::shared_ptr<_Literal> ptr = std::get<std::shared_ptr<_Literal>>(other.value);
+      assert(ptr != nullptr);
       value = std::move(other.value);
-      optr.reset();
+      ptr.reset();
       break;
     }
     case ExprType::UNARY: {
-      std::shared_ptr<_Unary> optr = std::get<std::shared_ptr<_Unary>>(other.value);
+      std::shared_ptr<_Unary> ptr = std::get<std::shared_ptr<_Unary>>(other.value);
+      assert(ptr != nullptr);
       value = std::move(other.value);
-      optr.reset();
+      ptr.reset();
       break;
     }
   }
diff --git a/cclox_src/parser/printer.hh b/cclox_src/parser/printer.hh
index fecd3e2..ec66745 100644
--- a/cclox_src/parser/printer.hh
+++ b/cclox_src/parser/printer.hh
@@ -1,11 +1,10 @@
-#ifndef PRINTER_HH
-#define PRINTER_HH
+#ifndef AST_PRINTER_HH
+#define AST_PRINTER_HH
 
 #include "expr.hh"
 #include <string>
 
-class AstPrinter {
-public:
+struct AstPrinter {
   std::string print(const Expr &expr);
 private:
   std::string parenthesize(const std::string &name, std::vector<const Expr *> exprs);