diff --git a/code/compiler/12/definition.cpp b/code/compiler/12/definition.cpp
index 551cf03..6d92133 100644
--- a/code/compiler/12/definition.cpp
+++ b/code/compiler/12/definition.cpp
@@ -26,8 +26,8 @@ void definition_defn::find_free(type_mgr& mgr, type_env_ptr& env) {
     body->find_free(mgr, var_env, free_variables);
 }
 
-void definition_defn::insert_types(type_mgr& mgr) {
-    env->bind(name, full_type);
+void definition_defn::insert_types(type_mgr& mgr, visibility v) {
+    env->bind(name, full_type, v);
 }
 
 void definition_defn::typecheck(type_mgr& mgr) {
@@ -150,7 +150,7 @@ void definition_group::typecheck(type_mgr& mgr) {
         auto& group = *it;
         for(auto& def_defnn_name : group->members) {
             auto& def_defn = defs_defn.find(def_defnn_name)->second;
-            def_defn->insert_types(mgr);
+            def_defn->insert_types(mgr, vis);
         }
         for(auto& def_defnn_name : group->members) {
             auto& def_defn = defs_defn.find(def_defnn_name)->second;
diff --git a/code/compiler/12/definition.hpp b/code/compiler/12/definition.hpp
index a2309b5..ce86bb3 100644
--- a/code/compiler/12/definition.hpp
+++ b/code/compiler/12/definition.hpp
@@ -44,7 +44,7 @@ struct definition_defn {
     }
 
     void find_free(type_mgr& mgr, type_env_ptr& env);
-    void insert_types(type_mgr& mgr);
+    void insert_types(type_mgr& mgr, visibility v);
     void typecheck(type_mgr& mgr);
     void compile();
     void declare_llvm(llvm_context& ctx);
@@ -76,9 +76,11 @@ using definition_data_ptr = std::unique_ptr<definition_data>;
 struct definition_group {
     std::map<std::string, definition_data_ptr> defs_data;
     std::map<std::string, definition_defn_ptr> defs_defn;
-
+    visibility vis;
     type_env_ptr env;
 
+    definition_group(visibility v = visibility::local) : vis(v) {}
+
     void find_free(type_mgr& mgr, type_env_ptr& env, std::set<std::string>& into);
     void typecheck(type_mgr& mgr);
 };
diff --git a/code/compiler/12/main.cpp b/code/compiler/12/main.cpp
index 2ec963c..c7d7234 100644
--- a/code/compiler/12/main.cpp
+++ b/code/compiler/12/main.cpp
@@ -33,10 +33,10 @@ void typecheck_program(
     type_ptr binop_type = type_ptr(new type_arr(
                 int_type_app,
                 type_ptr(new type_arr(int_type_app, int_type_app))));
-    env->bind("+", binop_type);
-    env->bind("-", binop_type);
-    env->bind("*", binop_type);
-    env->bind("/", binop_type);
+    env->bind("+", binop_type, visibility::global);
+    env->bind("-", binop_type, visibility::global);
+    env->bind("*", binop_type, visibility::global);
+    env->bind("/", binop_type, visibility::global);
 
     std::set<std::string> free;
     defs.find_free(mgr, env, free);
@@ -44,7 +44,7 @@ void typecheck_program(
 
     for(auto& pair : defs.env->names) {
         std::cout << pair.first << ": ";
-        pair.second->print(mgr, std::cout);
+        pair.second.type->print(mgr, std::cout);
         std::cout << std::endl;
     }
 }
diff --git a/code/compiler/12/parser.y b/code/compiler/12/parser.y
index bae7ad0..883879c 100644
--- a/code/compiler/12/parser.y
+++ b/code/compiler/12/parser.y
@@ -7,7 +7,7 @@
 #include "parser.hpp"
 #include "parsed_type.hpp"
 
-definition_group global_defs;
+definition_group global_defs(visibility::global);
 
 extern yy::parser::symbol_type yylex();
 
diff --git a/code/compiler/12/type_env.cpp b/code/compiler/12/type_env.cpp
index 26a5a84..e0fd33f 100644
--- a/code/compiler/12/type_env.cpp
+++ b/code/compiler/12/type_env.cpp
@@ -4,7 +4,7 @@
 void type_env::find_free(const type_mgr& mgr, std::set<std::string>& into) const {
     if(parent != nullptr) parent->find_free(mgr, into);
     for(auto& binding : names) {
-        mgr.find_free(binding.second, into);
+        mgr.find_free(binding.second.type, into);
     }
 }
 
@@ -13,13 +13,13 @@ void type_env::find_free_except(const type_mgr& mgr, const std::string& avoid,
     if(parent != nullptr) parent->find_free(mgr, into);
     for(auto& binding : names) {
         if(binding.first == avoid) continue;
-        mgr.find_free(binding.second, into);
+        mgr.find_free(binding.second.type, into);
     }
 }
 
 type_scheme_ptr type_env::lookup(const std::string& name) const {
     auto it = names.find(name);
-    if(it != names.end()) return it->second;
+    if(it != names.end()) return it->second.type;
     if(parent) return parent->lookup(name);
     return nullptr;
 }
@@ -31,12 +31,13 @@ type_ptr type_env::lookup_type(const std::string& name) const {
     return nullptr;
 }
 
-void type_env::bind(const std::string& name, type_ptr t) {
-    names[name] = type_scheme_ptr(new type_scheme(t));
+void type_env::bind(const std::string& name, type_ptr t, visibility v) {
+    type_scheme_ptr new_scheme(new type_scheme(std::move(t)));
+    names[name] = variable_data(std::move(new_scheme), v);
 }
 
-void type_env::bind(const std::string& name, type_scheme_ptr t) {
-    names[name] = t;
+void type_env::bind(const std::string& name, type_scheme_ptr t, visibility v) {
+    names[name] = variable_data(std::move(t), v);
 }
 
 void type_env::bind_type(const std::string& type_name, type_ptr t) {
@@ -47,15 +48,15 @@ void type_env::bind_type(const std::string& type_name, type_ptr t) {
 void type_env::generalize(const std::string& name, type_mgr& mgr) {
     auto names_it = names.find(name);
     if(names_it == names.end()) throw 0;
-    if(names_it->second->forall.size() > 0) throw 0;
+    if(names_it->second.type->forall.size() > 0) throw 0;
 
     std::set<std::string> free_in_type;
     std::set<std::string> free_in_env;
-    mgr.find_free(names_it->second->monotype, free_in_type);
+    mgr.find_free(names_it->second.type->monotype, free_in_type);
     find_free_except(mgr, name, free_in_env);
     for(auto& free : free_in_type) {
         if(free_in_env.find(free) != free_in_env.end()) continue;
-        names_it->second->forall.push_back(free);
+        names_it->second.type->forall.push_back(free);
     }
 }
 
diff --git a/code/compiler/12/type_env.hpp b/code/compiler/12/type_env.hpp
index 9b529d2..f61a674 100644
--- a/code/compiler/12/type_env.hpp
+++ b/code/compiler/12/type_env.hpp
@@ -7,9 +7,21 @@
 struct type_env;
 using type_env_ptr = std::shared_ptr<type_env>;
 
+enum class visibility { global,local };
+
 struct type_env {
+    struct variable_data {
+        type_scheme_ptr type;
+        visibility vis;
+
+        variable_data()
+            : variable_data(nullptr, visibility::local) {}
+        variable_data(type_scheme_ptr t, visibility v)
+            : type(std::move(t)), vis(v) {}
+    };
+
     type_env_ptr parent;
-    std::map<std::string, type_scheme_ptr> names;
+    std::map<std::string, variable_data> names;
     std::map<std::string, type_ptr> type_names;
 
     type_env(type_env_ptr p) : parent(std::move(p)) {}
@@ -20,8 +32,10 @@ struct type_env {
             std::set<std::string>& into) const;
     type_scheme_ptr lookup(const std::string& name) const;
     type_ptr lookup_type(const std::string& name) const;
-    void bind(const std::string& name, type_ptr t);
-    void bind(const std::string& name, type_scheme_ptr t);
+    void bind(const std::string& name, type_ptr t,
+            visibility v = visibility::local);
+    void bind(const std::string& name, type_scheme_ptr t,
+            visibility v = visibility::local);
     void bind_type(const std::string& type_name, type_ptr t);
     void generalize(const std::string& name, type_mgr& mgr);
 };