diff --git a/code/compiler/13/env.hpp b/code/compiler/13/env.hpp
index 9d0dfbe..5413bba 100644
--- a/code/compiler/13/env.hpp
+++ b/code/compiler/13/env.hpp
@@ -2,33 +2,38 @@
 #include <memory>
 #include <string>
 
-struct env {
-    virtual ~env() = default;
+class env {
+    public:
+        virtual ~env() = default;
 
-    virtual int get_offset(const std::string& name) const = 0;
-    virtual bool has_variable(const std::string& name) const = 0;
+        virtual int get_offset(const std::string& name) const = 0;
+        virtual bool has_variable(const std::string& name) const = 0;
 };
 
 using env_ptr = std::shared_ptr<env>;
 
-struct env_var : public env {
-    std::string name;
-    env_ptr parent;
+class env_var : public env {
+    private:
+        std::string name;
+        env_ptr parent;
 
-    env_var(std::string n, env_ptr p)
-        : name(std::move(n)), parent(std::move(p)) {}
+    public:
+        env_var(std::string n, env_ptr p)
+            : name(std::move(n)), parent(std::move(p)) {}
 
-    int get_offset(const std::string& name) const;
-    bool has_variable(const std::string& name) const;
+        int get_offset(const std::string& name) const;
+        bool has_variable(const std::string& name) const;
 };
 
-struct env_offset : public env {
-    int offset;
-    env_ptr parent;
+class env_offset : public env {
+    private:
+        int offset;
+        env_ptr parent;
 
-    env_offset(int o, env_ptr p)
-        : offset(o), parent(std::move(p)) {}
+    public:
+        env_offset(int o, env_ptr p)
+            : offset(o), parent(std::move(p)) {}
 
-    int get_offset(const std::string& name) const;
-    bool has_variable(const std::string& name) const;
+        int get_offset(const std::string& name) const;
+        bool has_variable(const std::string& name) const;
 };