diff --git a/README.md b/README.md
index e0f9b5d..6903e26 100644
--- a/README.md
+++ b/README.md
@@ -36,7 +36,7 @@ program = [ "type" type_definitions ";" ]
     [ variable_part ]
     compound_statement ".";
 
-procedure_definition = "proc" ident formal_parameter_list ";" block ";";
+procedure_definition = "proc" ident formal_parameter_list ";" ( block | "extern" ) ";";
 
 block = [ constant_part ]
     [ variable_part ]
diff --git a/example.elna b/example.elna
index c2b216c..d56148f 100644
--- a/example.elna
+++ b/example.elna
@@ -119,6 +119,8 @@ begin
   writei(x)
 end;
 
+proc exit(code: Int); extern;
+
 begin
   test_primitive();
   test_string();
@@ -129,5 +131,7 @@ begin
   test_if();
   test_not();
   test_param(8, 7);
-  test_const_char()
+  test_const_char();
+
+  exit(0)
 end.
diff --git a/gcc/elna-generic.cc b/gcc/elna-generic.cc
index 988c82f..6e6bfe8 100644
--- a/gcc/elna-generic.cc
+++ b/gcc/elna-generic.cc
@@ -132,12 +132,14 @@ namespace gcc
 
         enter_scope();
 
-        for (const auto& definition : program->value_definitions)
+        for (const auto definition : program->value_definitions)
         {
             definition->accept(this);
         }
-        program->body().accept(this);
-
+        for (const auto body_statement : program->body)
+        {
+            body_statement->accept(this);
+        }
         append_to_statement_list(return_stmt, &this->current_statements);
         tree_symbol_mapping mapping = leave_scope();
 
@@ -155,53 +157,64 @@ namespace gcc
 
     void generic_visitor::visit(source::procedure_definition *definition)
     {
-        std::vector<tree> parameter_types(definition->parameters().size());
+        std::vector<tree> parameter_types(definition->parameters.size());
 
-        for (std::size_t i = 0; i < definition->parameters().size(); ++i)
+        for (std::size_t i = 0; i < definition->parameters.size(); ++i)
         {
-            parameter_types[i] = build_type(definition->parameters().at(i)->type());
+            parameter_types[i] = build_type(definition->parameters.at(i)->type());
         }
         tree declaration_type = build_function_type_array(void_type_node,
-                definition->parameters().size(), parameter_types.data());
+                definition->parameters.size(), parameter_types.data());
         this->main_fndecl = build_fn_decl(definition->identifier().c_str(), declaration_type);
-
         this->symbol_map->enter(definition->identifier(), source::make_info(this->main_fndecl));
 
-        tree resdecl = build_decl(UNKNOWN_LOCATION, RESULT_DECL,
-                NULL_TREE, TREE_TYPE(TREE_TYPE(this->main_fndecl)));
-        DECL_CONTEXT(resdecl) = this->main_fndecl;
-        DECL_RESULT(this->main_fndecl) = resdecl;
-
-        enter_scope();
-
-        gcc::tree_chain argument_chain;
-        for (std::size_t i = 0; i < definition->parameters().size(); ++i)
+        if (definition->body() != nullptr)
         {
-            auto parameter = definition->parameters().at(i);
+            tree resdecl = build_decl(UNKNOWN_LOCATION, RESULT_DECL,
+                    NULL_TREE, TREE_TYPE(TREE_TYPE(this->main_fndecl)));
+            DECL_CONTEXT(resdecl) = this->main_fndecl;
+            DECL_RESULT(this->main_fndecl) = resdecl;
+
+            enter_scope();
+        }
+        gcc::tree_chain argument_chain;
+        for (std::size_t i = 0; i < definition->parameters.size(); ++i)
+        {
+            auto parameter = definition->parameters.at(i);
 
             tree declaration_tree = build_decl(get_location(&parameter->position()), PARM_DECL,
                 get_identifier(parameter->identifier().c_str()), parameter_types[i]);
             DECL_CONTEXT(declaration_tree) = this->main_fndecl;
             DECL_ARG_TYPE(declaration_tree) = parameter_types[i];
 
-            this->symbol_map->enter(parameter->identifier(), source::make_info(declaration_tree));
+            if (definition->body() != nullptr)
+            {
+                this->symbol_map->enter(parameter->identifier(), source::make_info(declaration_tree));
+            }
             argument_chain.append(declaration_tree);
         }
         DECL_ARGUMENTS(this->main_fndecl) = argument_chain.head();
-        definition->body().accept(this);
 
-        tree_symbol_mapping mapping = leave_scope();
+        if (definition->body() != nullptr)
+        {
+            definition->body()->accept(this);
+            tree_symbol_mapping mapping = leave_scope();
 
-        BLOCK_SUPERCONTEXT(mapping.block()) = this->main_fndecl;
-        DECL_INITIAL(this->main_fndecl) = mapping.block();
-        DECL_SAVED_TREE(this->main_fndecl) = mapping.bind_expression();
+            BLOCK_SUPERCONTEXT(mapping.block()) = this->main_fndecl;
+            DECL_INITIAL(this->main_fndecl) = mapping.block();
+            DECL_SAVED_TREE(this->main_fndecl) = mapping.bind_expression();
 
-        DECL_EXTERNAL(this->main_fndecl) = 0;
-        DECL_PRESERVE_P(this->main_fndecl) = 1;
+            DECL_EXTERNAL(this->main_fndecl) = 0;
+            DECL_PRESERVE_P(this->main_fndecl) = 1;
 
-        gimplify_function_tree(this->main_fndecl);
+            gimplify_function_tree(this->main_fndecl);
 
-        cgraph_node::finalize_function(this->main_fndecl, true);
+            cgraph_node::finalize_function(this->main_fndecl, true);
+        }
+        else
+        {
+            DECL_EXTERNAL(this->main_fndecl) = 1;
+        }
     }
 
     void generic_visitor::enter_scope()
diff --git a/include/elna/source/ast.h b/include/elna/source/ast.h
index 99ad8cc..dd99e53 100644
--- a/include/elna/source/ast.h
+++ b/include/elna/source/ast.h
@@ -386,21 +386,21 @@ namespace source
      */
     class procedure_definition : public definition
     {
-        block *m_body;
-        std::vector<variable_declaration *> m_parameters;
+        block *m_body{ nullptr };
 
     public:
+        std::vector<variable_declaration *> parameters;
+
         /**
          * \param position Source code position.
          * \param identifier Procedure name.
          * \param body Procedure body.
          */
         procedure_definition(const struct position position, const std::string& identifier,
-                block *body);
+                block *body = nullptr);
         virtual void accept(parser_visitor *visitor) override;
 
-        block& body();
-        std::vector<variable_declaration *>& parameters();
+        block *body();
 
         virtual ~procedure_definition() override;
     };
@@ -603,17 +603,14 @@ namespace source
 
     class block : public node
     {
-        statement *m_body;
-
     public:
         std::vector<definition *> value_definitions;
+        std::vector<statement *> body;
 
         block(const struct position position, std::vector<definition *>&& value_definitions,
-                statement *body);
+                std::vector<statement *>&& body);
         virtual void accept(parser_visitor *visitor) override;
 
-        statement& body();
-
         virtual ~block() override;
     };
 
@@ -623,7 +620,7 @@ namespace source
         std::vector<definition *> type_definitions;
 
         program(const struct position position, std::vector<definition *>&& type_definitions,
-                std::vector<definition *>&& value_definitions, statement *body);
+                std::vector<definition *>&& value_definitions, std::vector<statement *>&& body);
         virtual void accept(parser_visitor *visitor) override;
 
         virtual ~program() override;
diff --git a/source/ast.cc b/source/ast.cc
index 26d8480..fdbe984 100644
--- a/source/ast.cc
+++ b/source/ast.cc
@@ -18,11 +18,14 @@ namespace source
 
     void empty_visitor::visit(procedure_definition *definition)
     {
-        for (auto parameter : definition->parameters())
+        for (auto parameter : definition->parameters)
         {
             parameter->accept(this);
         }
-        definition->body().accept(this);
+        if (definition->body() != nullptr)
+        {
+            definition->body()->accept(this);
+        }
     }
 
     void empty_visitor::visit(type_definition *definition)
@@ -65,11 +68,14 @@ namespace source
 
     void empty_visitor::visit(block *block)
     {
-        for (const auto& definition : block->value_definitions)
+        for (const auto definition : block->value_definitions)
         {
             definition->accept(this);
         }
-        block->body().accept(this);
+        for (const auto body_statement : block->body)
+        {
+            body_statement->accept(this);
+        }
     }
 
     void empty_visitor::visit(program *program)
@@ -407,20 +413,18 @@ namespace source
         visitor->visit(this);
     }
 
-    block& procedure_definition::body()
+    block *procedure_definition::body()
     {
-        return *m_body;
-    }
-
-    std::vector<variable_declaration *>& procedure_definition::parameters()
-    {
-        return m_parameters;
+        return m_body;
     }
 
     procedure_definition::~procedure_definition()
     {
-        delete m_body;
-        for (auto parameter : m_parameters)
+        if (m_body != nullptr)
+        {
+            delete m_body;
+        }
+        for (auto parameter : parameters)
         {
             delete parameter;
         }
@@ -448,8 +452,8 @@ namespace source
     }
 
     block::block(const struct position position, std::vector<definition *>&& value_definitions,
-            statement *body)
-        : node(position), m_body(std::move(body)), value_definitions(std::move(value_definitions))
+            std::vector<statement *>&& body)
+        : node(position), value_definitions(std::move(value_definitions)), body(std::move(body))
     {
     }
 
@@ -458,24 +462,22 @@ namespace source
         visitor->visit(this);
     }
 
-    statement& block::body()
-    {
-        return *m_body;
-    }
-
     block::~block()
     {
-        for (auto definition : value_definitions)
+        for (auto definition : this->value_definitions)
         {
             delete definition;
         }
-        delete m_body;
+        for (auto body_statement : this->body)
+        {
+            delete body_statement;
+        }
     }
 
     program::program(const struct position position,
             std::vector<definition *>&& type_definitions,
-            std::vector<definition *>&& value_definitions, statement *body)
-        : block(position, std::move(value_definitions), body),
+            std::vector<definition *>&& value_definitions, std::vector<statement *>&& body)
+        : block(position, std::move(value_definitions), std::move(body)),
         type_definitions(std::move(type_definitions))
     {
     }
diff --git a/source/lexer.ll b/source/lexer.ll
index c429c12..6f5c397 100644
--- a/source/lexer.ll
+++ b/source/lexer.ll
@@ -55,6 +55,9 @@ begin                   {
 end                     {
                             return yy::parser::make_END_BLOCK(this->location);
                         }
+extern                  {
+                            return yy::parser::make_EXTERN(this->location);
+                        }
 const                   {
                             return yy::parser::make_CONST(this->location);
                         }
diff --git a/source/parser.yy b/source/parser.yy
index 65db0aa..57aaf5a 100644
--- a/source/parser.yy
+++ b/source/parser.yy
@@ -64,7 +64,7 @@
 %token <bool> BOOLEAN
 %token IF WHILE DO
 %token CONST VAR PROCEDURE ARRAY OF TYPE RECORD
-%token BEGIN_BLOCK END_BLOCK
+%token BEGIN_BLOCK END_BLOCK EXTERN
 %token LEFT_PAREN RIGHT_PAREN LEFT_SQUARE RIGHT_SQUARE SEMICOLON DOT COMMA
 %token AND OR NOT
 %token GREATER_EQUAL LESS_EQUAL LESS_THAN GREATER_THAN NOT_EQUAL EQUALS
@@ -100,7 +100,7 @@
 %type <std::vector<std::pair<std::string, elna::source::type_expression *>>> field_list;
 %%
 program:
-    type_part constant_part procedure_part variable_part compound_statement DOT
+    type_part constant_part procedure_part variable_part BEGIN_BLOCK optional_statements END_BLOCK DOT
         {
             std::vector<elna::source::definition *> definitions($1.size() + $3.size());
             std::vector<elna::source::definition *>::iterator definition = definitions.begin();
@@ -124,11 +124,11 @@ program:
                 *value_definition++ = variable;
             }
             auto tree = new elna::source::program(elna::source::position{},
-                 std::move(definitions), std::move(value_definitions), std::move($5));
+                 std::move(definitions), std::move(value_definitions), std::move($6));
 
             driver.tree.reset(tree);
         }
-block: constant_part variable_part statement
+block: constant_part variable_part BEGIN_BLOCK optional_statements END_BLOCK
         {
             std::vector<elna::source::definition *> definitions($1.size() + $2.size());
             std::vector<elna::source::definition *>::iterator definition = definitions.begin();
@@ -142,15 +142,21 @@ block: constant_part variable_part statement
                 *definition++ = variable;
             }
             $$ = new elna::source::block(elna::source::position{},
-                 std::move(definitions), std::move($3));
-        };
+                 std::move(definitions), std::move($4));
+        }
 procedure_definition:
     PROCEDURE IDENTIFIER formal_parameter_list SEMICOLON block SEMICOLON
         {
             $$ = new elna::source::procedure_definition(elna::source::position{},
                  std::move($2), $5);
-            std::swap($$->parameters(), $3);
-        };
+            std::swap($$->parameters, $3);
+        }
+    | PROCEDURE IDENTIFIER formal_parameter_list SEMICOLON EXTERN SEMICOLON
+        {
+            $$ = new elna::source::procedure_definition(elna::source::position{},
+                 std::move($2));
+            std::swap($$->parameters, $3);
+        }
 procedure_definitions:
     procedure_definition procedure_definitions
         {