diff --git a/13/type.cpp b/13/type.cpp
index 4dd18e1..fb3ab68 100644
--- a/13/type.cpp
+++ b/13/type.cpp
@@ -26,9 +26,9 @@ type_ptr type_scheme::instantiate(type_mgr& mgr) const {
 }
 
 void type_var::print(const type_mgr& mgr, std::ostream& to) const {
-    auto it = mgr.types.find(name);
-    if(it != mgr.types.end()) {
-        it->second->print(mgr, to);
+    auto type = mgr.lookup(name);
+    if(type) {
+        type->print(mgr, to);
     } else {
         to << name;
     }
@@ -82,6 +82,12 @@ type_ptr type_mgr::new_arrow_type() {
     return type_ptr(new type_arr(new_type(), new_type()));
 }
 
+type_ptr type_mgr::lookup(const std::string& var) const {
+    auto types_it = types.find(var);
+    if(types_it != types.end()) return types_it->second;
+    return nullptr;
+}
+
 type_ptr type_mgr::resolve(type_ptr t, type_var*& var) const {
     type_var* cast;
 
diff --git a/13/type.hpp b/13/type.hpp
index af417b6..cb1d77e 100644
--- a/13/type.hpp
+++ b/13/type.hpp
@@ -7,7 +7,7 @@
 #include <optional>
 #include "location.hh"
 
-struct type_mgr;
+class type_mgr;
 
 struct type {
     virtual ~type() = default;
@@ -90,20 +90,23 @@ struct type_app : public type {
     void print(const type_mgr& mgr, std::ostream& to) const;
 };
 
-struct type_mgr {
-    int last_id = 0;
-    std::map<std::string, type_ptr> types;
+class type_mgr {
+    private:
+        int last_id = 0;
+        std::map<std::string, type_ptr> types;
 
-    std::string new_type_name();
-    type_ptr new_type();
-    type_ptr new_arrow_type();
+    public:
+        std::string new_type_name();
+        type_ptr new_type();
+        type_ptr new_arrow_type();
 
-    void unify(type_ptr l, type_ptr r, const std::optional<yy::location>& loc = std::nullopt);
-    type_ptr substitute(
-            const std::map<std::string, type_ptr>& subst,
-            const type_ptr& t) const;
-    type_ptr resolve(type_ptr t, type_var*& var) const;
-    void bind(const std::string& s, type_ptr t);
-    void find_free(const type_ptr& t, std::set<std::string>& into) const;
-    void find_free(const type_scheme_ptr& t, std::set<std::string>& into) const;
+        void unify(type_ptr l, type_ptr r, const std::optional<yy::location>& loc = std::nullopt);
+        type_ptr substitute(
+                const std::map<std::string, type_ptr>& subst,
+                const type_ptr& t) const;
+        type_ptr lookup(const std::string& var) const;
+        type_ptr resolve(type_ptr t, type_var*& var) const;
+        void bind(const std::string& s, type_ptr t);
+        void find_free(const type_ptr& t, std::set<std::string>& into) const;
+        void find_free(const type_scheme_ptr& t, std::set<std::string>& into) const;
 };