diff --git a/boot/dependency.cc b/boot/dependency.cc
index 9811422..0e268d4 100644
--- a/boot/dependency.cc
+++ b/boot/dependency.cc
@@ -17,31 +17,52 @@ along with GCC; see the file COPYING3.  If not see
 
 #include "elna/boot/dependency.h"
 
+#include <fstream>
+#include <sstream>
+#include <string.h>
+
 #include "elna/boot/driver.h"
+#include "elna/boot/semantic.h"
 #include "parser.hh"
 
 namespace elna::boot
 {
-    dependency_graph::dependency_graph()
+    source_path_error::source_path_error(const std::string& message, const char *path)
+        : error(path, { 0, 0 }), message(message)
     {
     }
 
-    dependency_graph::dependency_graph(error_list&& errors)
+    std::string source_path_error::what() const
+    {
+        std::stringstream output;
+        output << "Cannot open filename ";
+        output << this->path;
+        output << ": ";
+        output << this->message;
+
+        return output.str();
+    }
+
+    dependency::dependency()
+    {
+    }
+
+    dependency::dependency(error_list&& errors)
         : m_errors(std::move(errors))
     {
     }
 
-    bool dependency_graph::has_errors() const
+    bool dependency::has_errors() const
     {
         return !errors().empty();
     }
 
-    const error_list& dependency_graph::errors() const
+    const error_list& dependency::errors() const
     {
         return m_errors;
     }
 
-    dependency_graph read_sources(std::istream& entry_point, const char *entry_path)
+    dependency parse_source(std::istream& entry_point, const char *entry_path)
     {
         driver parse_driver{ entry_path };
         lexer tokenizer(entry_point);
@@ -49,14 +70,52 @@ namespace elna::boot
 
         if (parser())
         {
-            return dependency_graph(std::move(parse_driver.errors()));
+            return dependency(std::move(parse_driver.errors()));
         }
         else
         {
-            dependency_graph outcome;
-            outcome.modules.emplace_back(std::move(parse_driver.tree));
+            dependency outcome;
+            std::swap(outcome.tree, parse_driver.tree);
 
             return outcome;
         }
     }
+
+    dependency read_sources(const char *entry_path, std::shared_ptr<symbol_table> info_table,
+            std::shared_ptr<symbol_table> imports)
+    {
+        std::ifstream entry_point{ entry_path, std::ios::in };
+
+        if (!entry_point)
+        {
+            error_list errors;
+            errors.push_back(std::make_unique<source_path_error>(strerror(errno), entry_path));
+
+            return dependency(std::move(errors));
+        }
+        auto outcome = parse_source(entry_point, entry_path);
+
+        declaration_visitor declaration_visitor(entry_path);
+        outcome.tree->accept(&declaration_visitor);
+
+        if (!declaration_visitor.errors().empty())
+        {
+            return dependency(std::move(declaration_visitor.errors()));
+        }
+        outcome.unresolved = declaration_visitor.unresolved;
+        outcome.bag = symbol_bag{ std::move(declaration_visitor.unresolved), info_table };
+
+        if (imports != nullptr)
+        {
+            outcome.bag.add_import(imports);
+        }
+        elna::boot::name_analysis_visitor name_analysis_visitor(entry_path, outcome.bag);
+        outcome.tree->accept(&name_analysis_visitor);
+
+        if (!name_analysis_visitor.errors().empty())
+        {
+            return dependency(std::move(declaration_visitor.errors()));
+        }
+        return outcome;
+    }
 }
diff --git a/boot/parser.yy b/boot/parser.yy
index ab17bc9..af3f7a3 100644
--- a/boot/parser.yy
+++ b/boot/parser.yy
@@ -182,7 +182,7 @@ program:
         }
     | "module" ";" import_part constant_part type_part variable_part procedure_part "end" "."
         {
-            auto tree = new boot::program(boot::make_position(@1));
+            auto tree = new boot::unit(boot::make_position(@1));
 
             std::swap(tree->imports, $3);
             std::swap(tree->constants, $4);
diff --git a/boot/semantic.cc b/boot/semantic.cc
index 3ebccde..5489959 100644
--- a/boot/semantic.cc
+++ b/boot/semantic.cc
@@ -74,9 +74,8 @@ namespace elna::boot
         return message;
     }
 
-    name_analysis_visitor::name_analysis_visitor(const char *path, std::shared_ptr<symbol_table> symbols,
-                std::unordered_map<std::string, std::shared_ptr<alias_type>>&& unresolved)
-        : error_container(path), symbols(symbols), unresolved(std::move(unresolved))
+    name_analysis_visitor::name_analysis_visitor(const char *path, symbol_bag bag)
+        : error_container(path), bag(bag)
     {
     }
 
@@ -120,20 +119,20 @@ namespace elna::boot
     void name_analysis_visitor::visit(type_declaration *definition)
     {
         definition->body().accept(this);
-        auto unresolved_declaration = this->unresolved.at(definition->identifier.identifier);
+        auto unresolved_declaration = this->bag.unresolved.at(definition->identifier.identifier);
 
         unresolved_declaration->reference = this->current_type;
     }
 
     void name_analysis_visitor::visit(named_type_expression *type_expression)
     {
-        auto unresolved_alias = this->unresolved.find(type_expression->name);
+        auto unresolved_alias = this->bag.unresolved.find(type_expression->name);
 
-        if (unresolved_alias != this->unresolved.end())
+        if (unresolved_alias != this->bag.unresolved.end())
         {
             this->current_type = type(unresolved_alias->second);
         }
-        else if (auto from_symbol_table = this->symbols->lookup(type_expression->name))
+        else if (auto from_symbol_table = this->bag.lookup(type_expression->name))
         {
             this->current_type = from_symbol_table->is_type()->symbol;
         }
@@ -214,28 +213,24 @@ namespace elna::boot
     {
         declaration->variable_type().accept(this);
 
-        this->symbols->enter(declaration->identifier.identifier,
-                std::make_shared<variable_info>(this->current_type));
+        this->bag.enter(declaration->identifier.identifier, std::make_shared<variable_info>(this->current_type));
     }
 
     void name_analysis_visitor::visit(constant_declaration *definition)
     {
         definition->body().accept(this);
 
-        this->symbols->enter(definition->identifier.identifier,
-                std::make_shared<constant_info>(this->current_literal));
+        this->bag.enter(definition->identifier.identifier, std::make_shared<constant_info>(this->current_literal));
     }
 
     void name_analysis_visitor::visit(procedure_declaration *definition)
     {
         std::shared_ptr<procedure_info> info;
+        auto heading = build_procedure(definition->heading());
 
         if (definition->body.has_value())
         {
-            info = std::make_shared<procedure_info>(build_procedure(definition->heading()),
-                    definition->parameter_names, this->symbols);
-
-            this->symbols = info->symbols;
+            info = std::make_shared<procedure_info>(heading, definition->parameter_names, this->bag.enter());
 
             for (constant_declaration *const constant : definition->body.value().constants())
             {
@@ -249,14 +244,13 @@ namespace elna::boot
             {
                 statement->accept(this);
             }
-            this->symbols = this->symbols->scope();
+            this->bag.leave();
         }
         else
         {
-            info = std::make_shared<procedure_info>(build_procedure(definition->heading()),
-                    definition->parameter_names);
+            info = std::make_shared<procedure_info>(heading, definition->parameter_names);
         }
-        this->symbols->enter(definition->identifier.identifier, info);
+        this->bag.enter(definition->identifier.identifier, info);
     }
 
     void name_analysis_visitor::visit(assign_statement *statement)
@@ -379,14 +373,14 @@ namespace elna::boot
         {
             type->accept(this);
         }
-        for (auto& unresolved : this->unresolved)
+        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->symbols->enter(std::move(unresolved.first), info);
+                this->bag.enter(unresolved.first, info);
             }
             else
             {
diff --git a/boot/symbol.cc b/boot/symbol.cc
index a943774..b46cd8f 100644
--- a/boot/symbol.cc
+++ b/boot/symbol.cc
@@ -313,13 +313,9 @@ namespace elna::boot
     }
 
     procedure_info::procedure_info(const procedure_type symbol, const std::vector<std::string> names,
-            std::shared_ptr<symbol_table> parent_table)
-        : symbol(symbol), names(names)
+            std::shared_ptr<symbol_table> scope)
+        : symbol(symbol), names(names), symbols(scope)
     {
-        if (parent_table != nullptr)
-        {
-            this->symbols = std::make_shared<symbol_table>(parent_table);
-        }
     }
 
     std::shared_ptr<procedure_info> procedure_info::is_procedure()
@@ -361,4 +357,51 @@ namespace elna::boot
 
         return result;
     }
+
+    symbol_bag::symbol_bag()
+    {
+        this->symbols = std::make_shared<symbol_table>();
+        this->imports = std::make_shared<symbol_table>();
+    }
+
+    symbol_bag::symbol_bag(forward_table&& unresolved, std::shared_ptr<symbol_table> symbols)
+        : symbols(symbols), unresolved(unresolved)
+    {
+        this->imports = std::make_shared<symbol_table>();
+    }
+
+    std::shared_ptr<info> symbol_bag::lookup(const std::string& name)
+    {
+        if (auto result = this->imports->lookup(name))
+        {
+            return result;
+        }
+        return this->symbols->lookup(name);
+    }
+
+    bool symbol_bag::enter(const std::string& name, std::shared_ptr<info> entry)
+    {
+        return this->symbols->enter(name, entry);
+    }
+
+    std::shared_ptr<symbol_table> symbol_bag::enter()
+    {
+        this->symbols = std::make_shared<symbol_table>(this->symbols);
+        return this->symbols;
+    }
+
+    void symbol_bag::enter(std::shared_ptr<symbol_table> child)
+    {
+        this->symbols = child;
+    }
+
+    void symbol_bag::leave()
+    {
+        this->symbols = this->symbols->scope();
+    }
+
+    void symbol_bag::add_import(std::shared_ptr<symbol_table> table)
+    {
+        this->imports = table;
+    }
 }
diff --git a/gcc/elna-generic.cc b/gcc/elna-generic.cc
index 5deffde..07d0727 100644
--- a/gcc/elna-generic.cc
+++ b/gcc/elna-generic.cc
@@ -29,16 +29,14 @@ along with GCC; see the file COPYING3.  If not see
 #include "stringpool.h"
 #include "diagnostic.h"
 #include "realmpfr.h"
-#include "stor-layout.h"
 #include "varasm.h"
 #include "fold-const.h"
 #include "langhooks.h"
 
 namespace elna::gcc
 {
-    generic_visitor::generic_visitor(std::shared_ptr<symbol_table> symbol_table,
-            std::shared_ptr<boot::symbol_table> info_table)
-        : symbols(symbol_table), info_table(info_table)
+    generic_visitor::generic_visitor(std::shared_ptr<symbol_table> symbol_table, elna::boot::symbol_bag bag)
+        : symbols(symbol_table), bag(bag)
     {
     }
 
@@ -321,7 +319,7 @@ namespace elna::gcc
         DECL_STRUCT_FUNCTION(fndecl)->language = ggc_cleared_alloc<language_function>();
 
         enter_scope();
-        this->info_table = this->info_table->lookup(definition->identifier.identifier)->is_procedure()->symbols;
+        this->bag.enter(this->bag.lookup(definition->identifier.identifier)->is_procedure()->symbols);
 
         tree argument_chain = DECL_ARGUMENTS(fndecl);
         for (; argument_chain != NULL_TREE; argument_chain = TREE_CHAIN(argument_chain))
@@ -339,7 +337,7 @@ namespace elna::gcc
         visit_statements(definition->body.value().body());
 
         tree mapping = leave_scope();
-        this->info_table = this->info_table->scope();
+        this->bag.leave();
 
         BLOCK_SUPERCONTEXT(BIND_EXPR_BLOCK(mapping)) = fndecl;
         DECL_INITIAL(fndecl) = BIND_EXPR_BLOCK(mapping);
@@ -746,7 +744,7 @@ namespace elna::gcc
     void generic_visitor::visit(boot::variable_declaration *declaration)
     {
         this->current_expression = get_inner_alias(
-                this->info_table->lookup(declaration->identifier.identifier)->is_variable()->symbol,
+                this->bag.lookup(declaration->identifier.identifier)->is_variable()->symbol,
                 this->symbols);
 
         location_t declaration_location = get_location(&declaration->position());
diff --git a/gcc/elna1.cc b/gcc/elna1.cc
index ef13c57..9991778 100644
--- a/gcc/elna1.cc
+++ b/gcc/elna1.cc
@@ -64,15 +64,17 @@ static bool elna_langhook_init(void)
 
 static void elna_parse_file(const char *filename)
 {
-    std::ifstream file{ filename, std::ios::in };
-
-    if (!file)
-    {
-        fatal_error(UNKNOWN_LOCATION, "cannot open filename %s: %m", filename);
-    }
-    elna::boot::dependency_graph outcome = elna::boot::read_sources(file, filename);
-
     std::shared_ptr<elna::boot::symbol_table> info_table = elna::boot::builtin_symbol_table();
+    auto x = std::make_shared<elna::boot::symbol_table>(info_table);
+    elna::boot::dependency dependency = elna::boot::read_sources("source/Common.elna", x);
+
+    linemap_add(line_table, LC_ENTER, 0, "source/Common.elna", 1);
+    if (dependency.has_errors())
+    {
+        elna::gcc::report_errors(dependency.errors());
+    }
+    auto y = std::make_shared<elna::boot::symbol_table>(info_table);
+    elna::boot::dependency outcome = elna::boot::read_sources(filename, y, x);
     std::shared_ptr<elna::gcc::symbol_table> symbol_table = elna::gcc::builtin_symbol_table();
 
     linemap_add(line_table, LC_ENTER, 0, filename, 1);
@@ -82,34 +84,11 @@ static void elna_parse_file(const char *filename)
     }
     else
     {
-        for (const std::unique_ptr<elna::boot::program>& module_tree : outcome.modules)
-        {
-            elna::boot::declaration_visitor declaration_visitor(filename);
-            declaration_visitor.visit(module_tree.get());
+        elna::gcc::rewrite_symbol_table(x, symbol_table);
+        elna::gcc::rewrite_symbol_table(y, symbol_table);
 
-            if (declaration_visitor.errors().empty())
-            {
-                elna::boot::name_analysis_visitor name_analysis_visitor(filename, info_table,
-                        std::move(declaration_visitor.unresolved));
-                name_analysis_visitor.visit(module_tree.get());
-
-                if (name_analysis_visitor.errors().empty())
-                {
-                    elna::gcc::rewrite_symbol_table(info_table, symbol_table);
-
-                    elna::gcc::generic_visitor generic_visitor{ symbol_table, info_table };
-                    generic_visitor.visit(module_tree.get());
-                }
-                else
-                {
-                    elna::gcc::report_errors(name_analysis_visitor.errors());
-                }
-            }
-            else
-            {
-                elna::gcc::report_errors(declaration_visitor.errors());
-            }
-        }
+        elna::gcc::generic_visitor generic_visitor{ symbol_table, outcome.bag };
+        outcome.tree->accept(&generic_visitor);
     }
     linemap_add(line_table, LC_LEAVE, 0, NULL, 0);
 }
diff --git a/include/elna/boot/dependency.h b/include/elna/boot/dependency.h
index 64ed7dd..7a28f41 100644
--- a/include/elna/boot/dependency.h
+++ b/include/elna/boot/dependency.h
@@ -17,25 +17,39 @@ along with GCC; see the file COPYING3.  If not see
 
 #pragma once
 
+#include <filesystem>
 #include <fstream>
 #include "elna/boot/result.h"
 #include "elna/boot/ast.h"
 
 namespace elna::boot
 {
-    class dependency_graph
+    class source_path_error : public error
+    {
+        const std::string message;
+
+    public:
+        source_path_error(const std::string& message, const char *path);
+
+        std::string what() const override;
+    };
+
+    class dependency
     {
         error_list m_errors;
 
     public:
-        std::vector<std::unique_ptr<program>> modules;
+        std::unique_ptr<unit> tree;
+        std::unordered_map<std::string, std::shared_ptr<alias_type>> unresolved;
+        symbol_bag bag;
 
         bool has_errors() const;
         const error_list& errors() const;
 
-        dependency_graph();
-        explicit dependency_graph(error_list&& errors);
+        dependency();
+        explicit dependency(error_list&& errors);
     };
 
-    dependency_graph read_sources(std::istream& entry_point, const char *entry_path);
+    dependency read_sources(const char *entry_path, std::shared_ptr<symbol_table> info_table,
+            std::shared_ptr<symbol_table> imports = nullptr);
 }
diff --git a/include/elna/boot/driver.h b/include/elna/boot/driver.h
index c9706bd..288aa0c 100644
--- a/include/elna/boot/driver.h
+++ b/include/elna/boot/driver.h
@@ -39,7 +39,7 @@ namespace elna::boot
     class driver : public error_container
     {
     public:
-        std::unique_ptr<program> tree;
+        std::unique_ptr<unit> tree;
 
         driver(const char *input_file);
     };
diff --git a/include/elna/boot/semantic.h b/include/elna/boot/semantic.h
index d8d87d6..a510c3c 100644
--- a/include/elna/boot/semantic.h
+++ b/include/elna/boot/semantic.h
@@ -77,8 +77,7 @@ namespace elna::boot
         type current_type;
         constant_info::variant current_literal;
 
-        std::shared_ptr<symbol_table> symbols;
-        std::unordered_map<std::string, std::shared_ptr<alias_type>> unresolved;
+        symbol_bag bag;
 
         procedure_type build_procedure(procedure_type_expression& type_expression);
         std::vector<type_field> build_composite_type(const std::vector<field_declaration>& fields);
@@ -87,8 +86,7 @@ namespace elna::boot
                 std::vector<std::string>& path);
 
     public:
-        explicit name_analysis_visitor(const char *path, std::shared_ptr<symbol_table> symbols,
-                std::unordered_map<std::string, std::shared_ptr<alias_type>>&& unresolved);
+        name_analysis_visitor(const char *path, symbol_bag bag);
 
         void visit(named_type_expression *type_expression) override;
         void visit(array_type_expression *type_expression) override;
diff --git a/include/elna/boot/symbol.h b/include/elna/boot/symbol.h
index d28c656..365d3b6 100644
--- a/include/elna/boot/symbol.h
+++ b/include/elna/boot/symbol.h
@@ -281,6 +281,7 @@ namespace elna::boot
     };
 
     using symbol_table = symbol_map<std::shared_ptr<info>, std::nullptr_t, nullptr>;
+    using forward_table = std::unordered_map<std::string, std::shared_ptr<alias_type>>;
 
     class type_info : public info
     {
@@ -299,7 +300,7 @@ namespace elna::boot
         std::shared_ptr<symbol_table> symbols;
 
         procedure_info(const procedure_type symbol, const std::vector<std::string> names,
-                std::shared_ptr<symbol_table> parent_table = nullptr);
+                std::shared_ptr<symbol_table> scope = nullptr);
         std::shared_ptr<procedure_info> is_procedure() override;
     };
 
@@ -325,4 +326,24 @@ namespace elna::boot
     };
 
     std::shared_ptr<symbol_table> builtin_symbol_table();
+
+    class symbol_bag
+    {
+        std::shared_ptr<symbol_table> symbols;
+        std::shared_ptr<symbol_table> imports;
+
+    public:
+        forward_table unresolved;
+
+        symbol_bag();
+        symbol_bag(forward_table&& unresolved, std::shared_ptr<symbol_table> symbols);
+
+        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);
+    };
 }
diff --git a/include/elna/gcc/elna-generic.h b/include/elna/gcc/elna-generic.h
index aabfce2..54cad5d 100644
--- a/include/elna/gcc/elna-generic.h
+++ b/include/elna/gcc/elna-generic.h
@@ -36,8 +36,8 @@ namespace elna::gcc
     class generic_visitor final : public boot::parser_visitor
     {
         tree current_expression{ NULL_TREE };
+        elna::boot::symbol_bag bag;
         std::shared_ptr<symbol_table> symbols;
-        std::shared_ptr<boot::symbol_table> info_table;
 
         void enter_scope();
         tree leave_scope();
@@ -63,7 +63,7 @@ namespace elna::gcc
         bool assert_constant(location_t expression_location);
 
     public:
-        generic_visitor(std::shared_ptr<symbol_table> symbol_table, std::shared_ptr<boot::symbol_table> info_table);
+        generic_visitor(std::shared_ptr<symbol_table> symbol_table, elna::boot::symbol_bag bag);
 
         void visit(boot::program *program) override;
         void visit(boot::procedure_declaration *definition) override;
diff --git a/source/Common.def b/source/Common.def
deleted file mode 100644
index 9520230..0000000
--- a/source/Common.def
+++ /dev/null
@@ -1,12 +0,0 @@
-DEFINITION MODULE Common;
-
-TYPE
-  ShortString = ARRAY[1..256] OF CHAR;
-  Identifier = ARRAY[1..256] OF CHAR;
-  PIdentifier = POINTER TO Identifier;
-  TextLocation = RECORD
-    line: CARDINAL;
-    column: CARDINAL
-  END;
-
-END Common.
diff --git a/source/Common.elna b/source/Common.elna
index fa158b7..9d2185d 100644
--- a/source/Common.elna
+++ b/source/Common.elna
@@ -1,3 +1,12 @@
 module;
 
+type
+  ShortString = [256]Char;
+  Identifier = [256]Char;
+  PIdentifier = ^Identifier;
+  TextLocation* = record
+    line: Word;
+    column: Word
+  end;
+
 end.
diff --git a/source/main.elna b/source/main.elna
index 946e32e..939639d 100644
--- a/source/main.elna
+++ b/source/main.elna
@@ -80,13 +80,9 @@ type
     _module,
     _import
   );
-  Position* = record
-    line: Word;
-    column: Word
-  end;
   Location* = record
-    first: Position;
-    last: Position
+    first: TextLocation;
+    last: TextLocation
   end;
   SourceFile* = record
     buffer: [1024]Char;
@@ -101,7 +97,7 @@ type
     capacity: Word
   end;
   SourceCode = record
-    position: Position;
+    position: TextLocation;
 
     input: Pointer;
     empty: proc(Pointer) -> Bool;
@@ -1068,7 +1064,7 @@ begin
 	  fclose(source_file^.handle)
 	end;
 
-	source_code.position := Position(1u, 1u);
+	source_code.position := TextLocation(1u, 1u);
 	source_code.input := cast(source_file: Pointer);
 	source_code.empty := source_file_empty;
 	source_code.head := source_file_head;