diff --git a/boot/dependency.cc b/boot/dependency.cc
index 88e9bd5..6b10611 100644
--- a/boot/dependency.cc
+++ b/boot/dependency.cc
@@ -69,7 +69,7 @@ namespace elna::boot
         {
             return std::move(name_analyser.errors());
         }
-        type_analysis_visitor type_analyzer(path);
+        type_analysis_visitor type_analyzer(path, bag);
         tree->accept(&type_analyzer);
 
         if (type_analyzer.has_errors())
diff --git a/boot/result.cc b/boot/result.cc
index fe55410..dab82f4 100644
--- a/boot/result.cc
+++ b/boot/result.cc
@@ -48,4 +48,20 @@ namespace elna::boot
     {
         return !m_errors.empty();
     }
+
+    bool identifier_definition::operator==(const identifier_definition& that) const
+    {
+        return *this == that.name;
+    }
+
+    bool identifier_definition::operator==(const std::string& that) const
+    {
+        return this->name == that;
+    }
+}
+
+std::size_t std::hash<elna::boot::identifier_definition>::operator()(
+        const elna::boot::identifier_definition& key) const
+{
+    return std::hash<std::string>{}(key.name);
 }
diff --git a/boot/semantic.cc b/boot/semantic.cc
index e6dd248..b343f56 100644
--- a/boot/semantic.cc
+++ b/boot/semantic.cc
@@ -93,8 +93,8 @@ namespace elna::boot
         return "Only one variable can be initialized";
     }
 
-    type_analysis_visitor::type_analysis_visitor(const char *path)
-        : error_container(path)
+    type_analysis_visitor::type_analysis_visitor(const char *path, symbol_bag bag)
+        : error_container(path), bag(bag)
     {
     }
 
@@ -113,7 +113,7 @@ namespace elna::boot
             }
             if (!this->returns)
             {
-                add_error<return_error>(definition->identifier.identifier, this->input_file, definition->position());
+                add_error<return_error>(definition->identifier.name, this->input_file, definition->position());
             }
         }
     }
@@ -126,10 +126,6 @@ namespace elna::boot
     {
     }
 
-    void type_analysis_visitor::visit(import_declaration *)
-    {
-    }
-
     void type_analysis_visitor::visit(while_statement *)
     {
     }
@@ -151,8 +147,28 @@ namespace elna::boot
     {
     }
 
+    bool type_analysis_visitor::check_unresolved_symbol(std::shared_ptr<alias_type> alias,
+            std::vector<std::string>& alias_path)
+    {
+        if (std::find(std::cbegin(alias_path), std::cend(alias_path), alias->name) != std::cend(alias_path))
+        {
+            return false;
+        }
+        alias_path.push_back(alias->name);
+
+        if (auto another_alias = alias->reference.get<alias_type>())
+        {
+            return check_unresolved_symbol(another_alias, alias_path);
+        }
+        return true;
+    }
+
     void type_analysis_visitor::visit(unit *unit)
     {
+        for (type_declaration *const type : unit->types)
+        {
+            type->accept(this);
+        }
         for (procedure_declaration *const procedure : unit->procedures)
         {
             this->returns = false;
@@ -160,6 +176,17 @@ namespace elna::boot
         }
     }
 
+    void type_analysis_visitor::visit(type_declaration *definition)
+    {
+        std::vector<std::string> alias_path;
+        auto unresolved_type = this->bag.lookup(definition->identifier.name)->is_type()->symbol.get<alias_type>();
+
+        if (!check_unresolved_symbol(unresolved_type, alias_path))
+        {
+            add_error<cyclic_declaration_error>(alias_path, this->input_file, definition->position());
+        }
+    }
+
     name_analysis_visitor::name_analysis_visitor(const char *path, symbol_bag bag)
         : error_container(path), bag(bag)
     {
@@ -205,18 +232,20 @@ namespace elna::boot
     void name_analysis_visitor::visit(type_declaration *definition)
     {
         definition->body().accept(this);
-        auto unresolved_declaration = this->bag.unresolved.at(definition->identifier.identifier);
+        auto resolved = this->bag.resolve(definition->identifier.name, this->current_type);
+        auto info = std::make_shared<type_info>(type(resolved));
 
-        unresolved_declaration->reference = this->current_type;
+        info->exported = definition->identifier.exported;
+        this->bag.enter(definition->identifier.name, info);
     }
 
     void name_analysis_visitor::visit(named_type_expression *type_expression)
     {
-        auto unresolved_alias = this->bag.unresolved.find(type_expression->name);
+        auto unresolved_alias = this->bag.declared(type_expression->name);
 
-        if (unresolved_alias != this->bag.unresolved.end())
+        if (unresolved_alias != nullptr)
         {
-            this->current_type = type(unresolved_alias->second);
+            this->current_type = type(unresolved_alias);
         }
         else if (auto from_symbol_table = this->bag.lookup(type_expression->name))
         {
@@ -301,15 +330,24 @@ namespace elna::boot
 
         for (const auto& variable_identifier : declaration->identifiers)
         {
-            this->bag.enter(variable_identifier.identifier, std::make_shared<variable_info>(this->current_type));
+            auto variable_symbol = std::make_shared<variable_info>(this->current_type, declaration->is_extern);
+
+            variable_symbol->exported = variable_identifier.exported;
+            if (!this->bag.enter(variable_identifier.name, variable_symbol))
+            {
+                add_error<already_declared_error>(variable_identifier.name, this->input_file,
+                        declaration->position());
+            }
         }
     }
 
     void name_analysis_visitor::visit(constant_declaration *definition)
     {
         definition->body().accept(this);
+        auto constant_symbol = std::make_shared<constant_info>(this->current_literal);
 
-        this->bag.enter(definition->identifier.identifier, std::make_shared<constant_info>(this->current_literal));
+        constant_symbol->exported = definition->identifier.exported;
+        this->bag.enter(definition->identifier.name, constant_symbol);
     }
 
     void name_analysis_visitor::visit(procedure_declaration *definition)
@@ -339,7 +377,8 @@ namespace elna::boot
         {
             info = std::make_shared<procedure_info>(heading, definition->parameter_names);
         }
-        this->bag.enter(definition->identifier.identifier, info);
+        info->exported = definition->identifier.exported;
+        this->bag.enter(definition->identifier.name, info);
     }
 
     void name_analysis_visitor::visit(assign_statement *statement)
@@ -440,42 +479,12 @@ namespace elna::boot
         }
     }
 
-    bool name_analysis_visitor::check_unresolved_symbol(std::shared_ptr<alias_type> alias,
-            std::vector<std::string>& path)
-    {
-        if (std::find(std::cbegin(path), std::cend(path), alias->name) != std::cend(path))
-        {
-            return false;
-        }
-        path.push_back(alias->name);
-
-        if (auto another_alias = alias->reference.get<alias_type>())
-        {
-            return check_unresolved_symbol(another_alias, path);
-        }
-        return true;
-    }
-
     void name_analysis_visitor::visit(unit *unit)
     {
         for (type_declaration *const type : unit->types)
         {
             type->accept(this);
         }
-        for (auto& unresolved : this->bag.unresolved)
-        {
-            std::vector<std::string> path;
-
-            if (check_unresolved_symbol(unresolved.second, path))
-            {
-                auto info = std::make_shared<type_info>(type_info(type(unresolved.second)));
-                this->bag.enter(unresolved.first, info);
-            }
-            else
-            {
-                add_error<cyclic_declaration_error>(path, this->input_file, position{ 0, 0 });
-            }
-        }
         for (variable_declaration *const variable : unit->variables)
         {
             variable->accept(this);
@@ -590,12 +599,7 @@ namespace elna::boot
         }
         for (type_declaration *const type : unit->types)
         {
-            const std::string& type_identifier = type->identifier.identifier;
-
-            if (!this->unresolved.insert({ type_identifier, std::make_shared<alias_type>(type_identifier) }).second)
-            {
-                add_error<already_declared_error>(type->identifier.identifier, this->input_file, type->position());
-            }
+            type->accept(this);
         }
         for (variable_declaration *const variable : unit->variables)
         {
@@ -607,6 +611,17 @@ namespace elna::boot
         }
     }
 
+    void declaration_visitor::visit(type_declaration *definition)
+    {
+        const std::string& type_identifier = definition->identifier.name;
+
+        if (!this->unresolved.insert({ type_identifier, std::make_shared<alias_type>(type_identifier) }).second)
+        {
+            add_error<already_declared_error>(definition->identifier.name, this->input_file,
+                    definition->position());
+        }
+    }
+
     void declaration_visitor::visit(variable_declaration *declaration)
     {
         if (declaration->has_initializer() && declaration->identifiers.size() > 1)
diff --git a/boot/symbol.cc b/boot/symbol.cc
index 1651cbb..902d331 100644
--- a/boot/symbol.cc
+++ b/boot/symbol.cc
@@ -314,7 +314,7 @@ namespace elna::boot
 
     procedure_info::procedure_info(const procedure_type symbol, const std::vector<std::string> names,
             std::shared_ptr<symbol_table> scope)
-        : symbol(symbol), names(names), symbols(scope)
+        : symbol(symbol), names(names), scope(scope)
     {
     }
 
@@ -323,6 +323,11 @@ namespace elna::boot
         return std::static_pointer_cast<procedure_info>(shared_from_this());
     }
 
+    bool procedure_info::is_extern() const
+    {
+        return this->scope == nullptr;
+    }
+
     constant_info::constant_info(const variant& symbol)
         : symbol(symbol)
     {
@@ -333,8 +338,8 @@ namespace elna::boot
         return std::static_pointer_cast<constant_info>(shared_from_this());
     }
 
-    variable_info::variable_info(const type symbol)
-        : symbol(symbol)
+    variable_info::variable_info(const type symbol, bool is_extern)
+        : symbol(symbol), is_extern(is_extern)
     {
     }
 
@@ -358,14 +363,10 @@ namespace elna::boot
         return result;
     }
 
-    symbol_bag::symbol_bag()
-    {
-        this->symbols = std::make_shared<symbol_table>();
-    }
-
-    symbol_bag::symbol_bag(forward_table&& unresolved, std::shared_ptr<symbol_table> symbols)
-        : symbols(symbols), unresolved(unresolved)
+    symbol_bag::symbol_bag(forward_table&& unresolved, std::shared_ptr<symbol_table> global_table)
+        : unresolved(unresolved)
     {
+        this->symbols = std::make_shared<symbol_table>(global_table);
     }
 
     std::shared_ptr<info> symbol_bag::lookup(const std::string& name)
@@ -396,18 +397,31 @@ namespace elna::boot
         this->symbols = child;
     }
 
-    void symbol_bag::leave()
+    std::shared_ptr<symbol_table> symbol_bag::leave()
     {
-        this->symbols = this->symbols->scope();
+        std::shared_ptr<symbol_table> result = this->symbols;
+
+        this->symbols = result->scope();
+        return result;
     }
 
-    void symbol_bag::add_import(std::shared_ptr<symbol_table> table)
+    std::shared_ptr<alias_type> symbol_bag::declared(const std::string& symbol_name)
     {
-        this->imports.push_front(table);
+        auto unresolved_alias = this->unresolved.find(symbol_name);
+
+        return unresolved_alias == this->unresolved.end() ? std::shared_ptr<alias_type>() : unresolved_alias->second;
+    }
+
+    std::shared_ptr<alias_type> symbol_bag::resolve(const std::string& symbol_name, type& resolution)
+    {
+        auto unresolved_declaration = this->unresolved.at(symbol_name);
+
+        unresolved_declaration->reference = resolution;
+        return unresolved_declaration;
     }
 
     void symbol_bag::add_import(const symbol_bag& bag)
     {
-        add_import(bag.symbols);
+        this->imports.push_front(bag.symbols);
     }
 }
diff --git a/gcc/elna-builtins.cc b/gcc/elna-builtins.cc
index 232cf28..a121bdc 100644
--- a/gcc/elna-builtins.cc
+++ b/gcc/elna-builtins.cc
@@ -87,7 +87,7 @@ namespace elna::gcc
         tree definition_tree = build_decl(UNKNOWN_LOCATION, TYPE_DECL,
                 get_identifier(identifier.c_str()), type);
 
-        TREE_PUBLIC(definition_tree) = true;
+        TREE_PUBLIC(definition_tree) = 1;
         if (is_unique_type(type))
         {
             TYPE_NAME(type) = DECL_NAME(definition_tree);
@@ -235,7 +235,21 @@ namespace elna::gcc
         }
         DECL_ARGUMENTS(fndecl) = argument_chain;
         TREE_ADDRESSABLE(fndecl) = 1;
-        DECL_EXTERNAL(fndecl) = info.symbols == nullptr;
+        DECL_EXTERNAL(fndecl) = info.is_extern();
+    }
+
+    tree declare_variable(const std::string& name, const boot::variable_info& info,
+            std::shared_ptr<symbol_table> symbols)
+    {
+        auto variable_type = get_inner_alias(info.symbol, symbols);
+        tree declaration_tree = build_decl(UNKNOWN_LOCATION, VAR_DECL, get_identifier(name.c_str()), variable_type);
+
+        TREE_ADDRESSABLE(declaration_tree) = 1;
+        DECL_EXTERNAL(declaration_tree) = info.is_extern;
+
+        symbols->enter(name, declaration_tree);
+
+        return declaration_tree;
     }
 
     void rewrite_symbol_table(std::shared_ptr<boot::symbol_table> info_table, std::shared_ptr<symbol_table> symbols)
@@ -250,6 +264,10 @@ namespace elna::gcc
                     handle_symbol(symbol_name, alias_type, symbols);
                 }
             }
+            else if (auto variable_info = symbol_info->is_variable())
+            {
+                declare_variable(symbol_name, *variable_info, symbols);
+            }
             else if (auto procedure_info = symbol_info->is_procedure())
             {
                 declare_procedure(symbol_name, *procedure_info, symbols);
diff --git a/gcc/elna-generic.cc b/gcc/elna-generic.cc
index 5472061..72f67eb 100644
--- a/gcc/elna-generic.cc
+++ b/gcc/elna-generic.cc
@@ -311,7 +311,7 @@ namespace elna::gcc
 
     void generic_visitor::visit(boot::procedure_declaration *definition)
     {
-        tree fndecl = this->symbols->lookup(definition->identifier.identifier);
+        tree fndecl = this->symbols->lookup(definition->identifier.name);
         TREE_PUBLIC(fndecl) = definition->identifier.exported;
 
         if (!definition->body.has_value())
@@ -323,7 +323,7 @@ namespace elna::gcc
         DECL_STRUCT_FUNCTION(fndecl)->language = ggc_cleared_alloc<language_function>();
 
         enter_scope();
-        this->bag.enter(this->bag.lookup(definition->identifier.identifier)->is_procedure()->symbols);
+        this->bag.enter(this->bag.lookup(definition->identifier.name)->is_procedure()->scope);
 
         tree argument_chain = DECL_ARGUMENTS(fndecl);
         for (; argument_chain != NULL_TREE; argument_chain = TREE_CHAIN(argument_chain))
@@ -713,8 +713,8 @@ namespace elna::gcc
             return;
         }
         tree definition_tree = build_decl(definition_location, CONST_DECL,
-                get_identifier(definition->identifier.identifier.c_str()), TREE_TYPE(this->current_expression));
-        auto result = this->symbols->enter(definition->identifier.identifier, definition_tree);
+                get_identifier(definition->identifier.name.c_str()), TREE_TYPE(this->current_expression));
+        auto result = this->symbols->enter(definition->identifier.name, definition_tree);
 
         if (result)
         {
@@ -733,29 +733,29 @@ namespace elna::gcc
         else
         {
             error_at(definition_location, "Variable '%s' already declared in this scope",
-                    definition->identifier.identifier.c_str());
+                    definition->identifier.name.c_str());
         }
         this->current_expression = NULL_TREE;
     }
 
     void generic_visitor::visit(boot::type_declaration *declaration)
     {
-        TREE_PUBLIC(this->symbols->lookup(declaration->identifier.identifier)) = declaration->identifier.exported;
+        TREE_PUBLIC(this->symbols->lookup(declaration->identifier.name)) = declaration->identifier.exported;
     }
 
     void generic_visitor::visit(boot::variable_declaration *declaration)
     {
         for (const auto& variable_identifier : declaration->identifiers)
         {
-            this->current_expression = get_inner_alias(
-                    this->bag.lookup(variable_identifier.identifier)->is_variable()->symbol,
-                    this->symbols);
-
             location_t declaration_location = get_location(&declaration->position());
-            tree declaration_tree = build_decl(declaration_location, VAR_DECL,
-                    get_identifier(variable_identifier.identifier.c_str()), this->current_expression);
-            bool result = this->symbols->enter(variable_identifier.identifier, declaration_tree);
+            tree declaration_tree = this->symbols->lookup(variable_identifier.name);
 
+            if (declaration_tree == NULL_TREE)
+            {
+                auto variable_symbol = this->bag.lookup(variable_identifier.name)->is_variable();
+
+                declaration_tree = declare_variable(variable_identifier.name, *variable_symbol, this->symbols);
+            }
             // Set initializer if given.
             if (declaration->body != nullptr)
             {
@@ -771,19 +771,14 @@ namespace elna::gcc
                             print_type(TREE_TYPE(this->current_expression)).c_str());
                 }
             }
-            else if (POINTER_TYPE_P(this->current_expression))
+            else if (!declaration->is_extern && POINTER_TYPE_P(TREE_TYPE(declaration_tree)))
             {
                 DECL_INITIAL(declaration_tree) = elna_pointer_nil_node;
             }
-            DECL_EXTERNAL(declaration_tree) = declaration->is_extern;
             TREE_PUBLIC(declaration_tree) = variable_identifier.exported;
             this->current_expression = NULL_TREE;
-            if (!result)
-            {
-                error_at(declaration_location, "Variable '%s' already declared in this scope",
-                        variable_identifier.identifier.c_str());
-            }
-            else if (lang_hooks.decls.global_bindings_p())
+
+            if (lang_hooks.decls.global_bindings_p())
             {
                 TREE_STATIC(declaration_tree) = 1;
                 varpool_node::get_create(declaration_tree);
diff --git a/gcc/elna1.cc b/gcc/elna1.cc
index 017f30a..cb643c3 100644
--- a/gcc/elna1.cc
+++ b/gcc/elna1.cc
@@ -66,7 +66,6 @@ using dependency_state = elna::boot::dependency_state<std::shared_ptr<elna::gcc:
 
 static elna::boot::dependency elna_parse_file(dependency_state& state, const char *filename)
 {
-    auto module_table = std::make_shared<elna::boot::symbol_table>(state.globals);
     std::ifstream entry_point{ filename, std::ios::in };
 
     if (!entry_point)
@@ -80,7 +79,7 @@ static elna::boot::dependency elna_parse_file(dependency_state& state, const cha
     {
         elna::gcc::report_errors(outcome.errors());
     }
-    elna::boot::symbol_bag outcome_bag = elna::boot::symbol_bag{ std::move(outcome.unresolved), module_table };
+    elna::boot::symbol_bag outcome_bag = elna::boot::symbol_bag{ std::move(outcome.unresolved), state.globals };
 
     for (const auto& sub_tree : outcome.tree->imports)
     {
@@ -102,7 +101,7 @@ static elna::boot::dependency elna_parse_file(dependency_state& state, const cha
         elna::gcc::report_errors(semantic_errors);
     }
     state.cache.insert({ filename, outcome_bag });
-    elna::gcc::rewrite_symbol_table(module_table, state.custom);
+    elna::gcc::rewrite_symbol_table(outcome_bag.leave(), state.custom);
     linemap_add(line_table, LC_LEAVE, 0, NULL, 0);
 
     return outcome;
diff --git a/include/elna/boot/ast.h b/include/elna/boot/ast.h
index ad531f4..f67575a 100644
--- a/include/elna/boot/ast.h
+++ b/include/elna/boot/ast.h
@@ -217,12 +217,6 @@ namespace elna::boot
         virtual literal_expression *is_literal();
     };
 
-    struct identifier_definition
-    {
-        std::string identifier;
-        bool exported;
-    };
-
     /**
      * Symbol definition.
      */
diff --git a/include/elna/boot/dependency.h b/include/elna/boot/dependency.h
index 962578f..98d65c5 100644
--- a/include/elna/boot/dependency.h
+++ b/include/elna/boot/dependency.h
@@ -21,6 +21,7 @@ along with GCC; see the file COPYING3.  If not see
 #include <fstream>
 #include "elna/boot/result.h"
 #include "elna/boot/ast.h"
+#include "elna/boot/symbol.h"
 
 namespace elna::boot
 {
diff --git a/include/elna/boot/result.h b/include/elna/boot/result.h
index 3b2c26d..9fc1849 100644
--- a/include/elna/boot/result.h
+++ b/include/elna/boot/result.h
@@ -106,4 +106,19 @@ namespace elna::boot
         T proper_type{};
         bool no_return{ false };
     };
+
+    struct identifier_definition
+    {
+        std::string name;
+        bool exported;
+
+        bool operator==(const identifier_definition& that) const;
+        bool operator==(const std::string& that) const;
+    };
 }
+
+template<>
+struct std::hash<elna::boot::identifier_definition>
+{
+    std::size_t operator()(const elna::boot::identifier_definition& key) const noexcept;
+};
diff --git a/include/elna/boot/semantic.h b/include/elna/boot/semantic.h
index 6648d60..c2a485f 100644
--- a/include/elna/boot/semantic.h
+++ b/include/elna/boot/semantic.h
@@ -93,22 +93,26 @@ namespace elna::boot
     class type_analysis_visitor final : public empty_visitor, public error_container
     {
         bool returns;
+        symbol_bag bag;
+
+        bool check_unresolved_symbol(std::shared_ptr<alias_type> alias,
+                std::vector<std::string>& path);
 
     public:
-        explicit type_analysis_visitor(const char *path);
+        explicit type_analysis_visitor(const char *path, symbol_bag bag);
 
         void visit(program *program) override;
 
         void visit(procedure_declaration *definition) override;
         void visit(assign_statement *) override;
         void visit(if_statement *) override;
-        void visit(import_declaration *) override;
         void visit(while_statement *) override;
         void visit(return_statement *) override;
         void visit(defer_statement *) override;
         void visit(case_statement *) override;
         void visit(procedure_call *) override;
         void visit(unit *unit) override;
+        void visit(type_declaration *definition) override;
     };
 
     /**
@@ -124,9 +128,6 @@ namespace elna::boot
         procedure_type build_procedure(procedure_type_expression& type_expression);
         std::vector<type_field> build_composite_type(const std::vector<field_declaration>& fields);
 
-        bool check_unresolved_symbol(std::shared_ptr<alias_type> alias,
-                std::vector<std::string>& path);
-
     public:
         name_analysis_visitor(const char *path, symbol_bag bag);
 
@@ -175,13 +176,14 @@ namespace elna::boot
     class declaration_visitor final : public empty_visitor, public error_container
     {
     public:
-        std::unordered_map<std::string, std::shared_ptr<alias_type>> unresolved;
+        forward_table unresolved;
 
         explicit declaration_visitor(const char *path);
 
         void visit(program *program) override;
         void visit(import_declaration *) override;
         void visit(unit *unit) override;
+        void visit(type_declaration *definition) override;
         void visit(variable_declaration *declaration) override;
         void visit(procedure_declaration *definition) override;
     };
diff --git a/include/elna/boot/symbol.h b/include/elna/boot/symbol.h
index 9a7b24c..5ef917e 100644
--- a/include/elna/boot/symbol.h
+++ b/include/elna/boot/symbol.h
@@ -161,6 +161,8 @@ namespace elna::boot
     class info : public std::enable_shared_from_this<info>
     {
     public:
+        bool exported{ false };
+
         virtual ~info() = 0;
 
         virtual std::shared_ptr<type_info> is_type();
@@ -231,6 +233,7 @@ namespace elna::boot
          * can not be found.
          *
          * \param name Symbol name.
+         *
          * \return Symbol from the table if found.
          */
         symbol_ptr lookup(const std::string& name)
@@ -250,6 +253,7 @@ namespace elna::boot
 
         /**
          * \param name Symbol name.
+         *
          * \return Whether the table contains a symbol with the given name.
          */
         bool contains(const std::string& name)
@@ -293,16 +297,37 @@ namespace elna::boot
         std::shared_ptr<type_info> is_type() override;
     };
 
+    /**
+     * Procedure symbol information.
+     */
     class procedure_info : public info
     {
     public:
+        /// Procedure type.
         const procedure_type symbol;
-        const std::vector<std::string> names;
-        std::shared_ptr<symbol_table> symbols;
 
+        /// Parameter names.
+        const std::vector<std::string> names;
+
+        /// Local definitions.
+        std::shared_ptr<symbol_table> scope;
+
+        /**
+         * Constructs procedure symbol information.
+         *
+         * \param symbol Procedure type.
+         * \param names Parameter names.
+         * \param scope Local definition (is `nullptr` for extern symbols).
+         */
         procedure_info(const procedure_type symbol, const std::vector<std::string> names,
                 std::shared_ptr<symbol_table> scope = nullptr);
+
         std::shared_ptr<procedure_info> is_procedure() override;
+
+        /**
+         * \return Whether this is an extern symbol.
+         */
+        bool is_extern() const;
     };
 
     class constant_info : public info
@@ -317,35 +342,116 @@ namespace elna::boot
         std::shared_ptr<constant_info> is_constant() override;
     };
 
+    /**
+     * Variable symbol information.
+     */
     class variable_info : public info
     {
     public:
+        /// Variable type.
         const type symbol;
 
-        variable_info(const type symbol);
+        /// Whether this is an extern symbol.
+        const bool is_extern;
+
+        /**
+         * Constructs a variable symbol information.
+         *
+         * \param symbol Variable type.
+         * \param is_extern Whether this is an extern symbol.
+         */
+        variable_info(const type symbol, bool is_extern);
+
         std::shared_ptr<variable_info> is_variable() override;
     };
 
     std::shared_ptr<symbol_table> builtin_symbol_table();
 
+    /**
+     * Symbol bag contains:
+     *
+     * - the symbol table of a module itself
+     * - symbol tables of imported modules
+     * - forward declarations
+     */
     class symbol_bag
     {
         std::shared_ptr<symbol_table> symbols;
         std::forward_list<std::shared_ptr<symbol_table>> imports;
-
-    public:
         forward_table unresolved;
 
-        symbol_bag();
-        symbol_bag(forward_table&& unresolved, std::shared_ptr<symbol_table> symbols);
+    public:
 
+        /**
+         * \param unresolved Forward declarations collected in the previous step.
+         * \param global_table Global symbols.
+         */
+        symbol_bag(forward_table&& unresolved, std::shared_ptr<symbol_table> global_table);
+
+        /**
+         * Looks up a symbol in the current and imported modules.
+         *
+         * \param name Symbol name to look up.
+         *
+         * \return Symbol from one of the symbol tables if found.
+         */
         std::shared_ptr<info> lookup(const std::string& name);
-        bool enter(const std::string& name, std::shared_ptr<info> entry);
-        std::shared_ptr<symbol_table> enter();
-        void enter(std::shared_ptr<symbol_table> child);
-        void leave();
 
-        void add_import(std::shared_ptr<symbol_table> table);
+        /**
+         * Inserts a symbol into the current scope.
+         *
+         * \param name Symbol name.
+         * \param entry Symbol info.
+         *
+         * \return Whether the insertion took place.
+         */
+        bool enter(const std::string& name, std::shared_ptr<info> entry);
+
+        /**
+         * Enters a new scope.
+         *
+         * \return Reference to the allocated scope.
+         */
+        std::shared_ptr<symbol_table> enter();
+
+        /**
+         * Sets the current scope to \a child.
+         *
+         * \param child New scope.
+         */
+        void enter(std::shared_ptr<symbol_table> child);
+
+        /**
+         * Leave the current scope.
+         *
+         * \return Left scope.
+         */
+        std::shared_ptr<symbol_table> leave();
+
+        /**
+         * Checks whether there is a forward declaration \a symbol_name and
+         * returns it if so.
+         *
+         * \param symbol_name Type name to look up.
+         * \return Forward declaration or `nullptr` if the symbol is not declared.
+         */
+        std::shared_ptr<alias_type> declared(const std::string& symbol_name);
+
+        /**
+         * Completes the forward-declared type \a symbol_name and defines it to
+         * be \a resolution.
+         *
+         * \param symbol_name Type name.
+         * \param resolution Type definition.
+         * \return Alias to the defined type.
+         */
+        std::shared_ptr<alias_type> resolve(const std::string& symbol_name, type& resolution);
+
+        /**
+         * Add imported symbols to the scope.
+         *
+         * \param bag Symbol bag of another module.
+         */
         void add_import(const symbol_bag& bag);
     };
 }
diff --git a/include/elna/gcc/elna-builtins.h b/include/elna/gcc/elna-builtins.h
index 1fe11e4..0cdf519 100644
--- a/include/elna/gcc/elna-builtins.h
+++ b/include/elna/gcc/elna-builtins.h
@@ -36,4 +36,6 @@ namespace elna::gcc
     tree get_inner_alias(const boot::type& type, std::shared_ptr<symbol_table> symbols);
     void declare_procedure(const std::string& name, const boot::procedure_info& info,
             std::shared_ptr<symbol_table> symbols);
+    tree declare_variable(const std::string& name, const boot::variable_info& info,
+            std::shared_ptr<symbol_table> symbols);
 }