diff --git a/README b/README
index b6e03eb..10ec738 100644
--- a/README
+++ b/README
@@ -1,37 +1,73 @@
 # Elna programming language
 
-Elna compiles simple mathematical operations to machine code.
-The compiled program returns the result of the operation.
+Elna is a simple, imperative, low-level programming language.
+
+It is intendet to accompany other languages in the areas, where a high-level
+language doesn't fit well. It is also supposed to be an intermediate
+representation for a such high-level hypothetical programming language.
 
 ## File extension
 
 .elna
 
-## Grammar PL/0
+## Current implementation
 
-program = block "." ;
+This repository contains a GCC frontend for Elna. After finishing the frontend
+I'm planning to rewrite the compiler in Elna itself with its own backend and
+a hand-written parser. So GCC gives a way to have a simple bootstrap compiler
+and a possbility to compile Elna programs for different platforms.
 
-block = [ "const" ident "=" number {"," ident "=" number} ";"]
-        [ "var" ident {"," ident} ";"]
-        { "procedure" ident ";" block ";" } statement ;
+## Grammar
 
-statement = [ ident ":=" expression | "call" ident 
-              | "?" ident | "!" expression 
-              | "begin" statement {";" statement } "end" 
-              | "if" condition "then" statement 
-              | "while" condition "do" statement ];
+digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9";
+
+integer = digit { digit };
+boolean = "true" | "false";
+
+program = [ "type" type_definitions ";" ]
+    [ "const" ident "=" integer { "," ident "=" integer } ";"]
+    { procedure_definition }
+    [ "var" variable_declarations ";" ]
+    compound_statement ".";
+
+procedure_definition = "procedure" ident formal_parameter_list ";" block ";";
+
+block = [ "const" ident "=" integer { "," ident "=" integer } ";" ]
+    [ "var" variable_declarations ";" ]
+    statement;
+
+statement = [ ident ":=" expression
+            | ident actual_parameter_list
+            | compound_statement
+            | "if" condition "then" statement 
+            | "while" condition "do" statement ];
+
+compound_statement = "begin" statement {";" statement } "end" ;
 
 condition = "odd" expression |
-            expression ("="|"#"|"<"|"<="|">"|">=") expression ;
+            expression ("="|"#"|"<"|"<="|">"|">=") expression;
 
 expression = [ "+"|"-"] term { ("+"|"-") term};
 
-term = factor {("*"|"/") factor};
+term = factor { ("*"|"/") factor };
 
-factor = ident | number | "(" expression ")";
+factor = ident | integer | "(" expression ")";
 
-## Operations
+formal_parameter_list = "(" [ variable_declarations ] ")";
 
-"!" - Write a line.
-"?" - Read user input.
-"odd" - The only function, returns whether a number is odd.
+actual_parameter_list = "(" [ expressions ] ")";
+
+expressions = expression { "," expression };
+
+variable_declarations = variable_declaration { ";" variable_declaration };
+
+variable_declaration = ident ":" type_expression;
+
+type_expression = "array" integer "of" type_expression
+                | "^" type_expression
+                | "record" field_list "end"
+                | ident;
+
+field_list = field_declaration { ";" field_declaration };
+
+field_declaration = ident ":" type_expression;
diff --git a/example.elna b/example.elna
index c07dead..d248d47 100644
--- a/example.elna
+++ b/example.elna
@@ -15,7 +15,7 @@ begin
 end;
 
 proc test_array();
-var a: T, x_3: Int;
+var a: T, x: Int;
 begin
   a[0] := 2;
   a[1] := 5;
@@ -23,19 +23,19 @@ begin
   writei("");
   writei("Test array:");
 
-  x_3 := 0;
-  while x_3 < 2 do
+  x := 0;
+  while x < 2 do
   begin
-    writei(a[x_3]);
-	x_3 := x_3 + 1
+    writei(a[x]);
+	x := x + 1
   end
 end;
 
 proc test_pointer();
-var x_2: Int, p: ^Int;
+var x: Int, p: ^Int;
 begin
-  x_2 := 5;
-  p := @x_2;
+  x := 5;
+  p := @x;
 
   writei("");
   writei("Test pointer:");
@@ -69,13 +69,13 @@ end;
 
 proc test_const();
 const t = 5;
-var x_1: Int;
+var x: Int;
 begin
-  x_1 := t;
+  x := t;
 
   writei("");
   writei("Test const:");
-  writei(x_1)
+  writei(x)
 end;
 
 proc test_if();
diff --git a/gcc/Make-lang.in b/gcc/Make-lang.in
index fdcebf1..e87da96 100644
--- a/gcc/Make-lang.in
+++ b/gcc/Make-lang.in
@@ -30,7 +30,6 @@ elna_OBJS = \
 	elna/lexer.o \
 	elna/parser.o \
 	elna/result.o \
-	elna/types.o \
 	$(END)
 
 elna1$(exeext): attribs.o $(elna_OBJS) $(BACKEND) $(LIBDEPS)
diff --git a/gcc/elna-generic.cc b/gcc/elna-generic.cc
index 24c00db..cc7990d 100644
--- a/gcc/elna-generic.cc
+++ b/gcc/elna-generic.cc
@@ -15,9 +15,14 @@ namespace elna
 {
 namespace gcc
 {
+    generic_visitor::generic_visitor()
+    {
+        this->symbol_map = std::make_shared<source::symbol_table<tree>>();
+    }
+
     void generic_visitor::visit(source::call_statement *statement)
     {
-        auto symbol = this->symbol_map.find(statement->name());
+        auto symbol = this->symbol_map->lookup(statement->name());
 
         if (statement->name() == "writei")
         {
@@ -80,10 +85,10 @@ namespace gcc
             append_to_statement_list(stmt, &this->current_statements);
             this->current_expression = NULL_TREE;
         }
-        else if (symbol != this->symbol_map.end())
+        else if (symbol)
         {
             tree fndecl_type = build_function_type_list(integer_type_node, NULL_TREE);
-            tree printf_fn = build1(ADDR_EXPR, build_pointer_type(fndecl_type), symbol->second);
+            tree printf_fn = build1(ADDR_EXPR, build_pointer_type(fndecl_type), symbol->payload);
 
             tree stmt = build_call_nary(integer_type_node, printf_fn, 0);
 
@@ -100,7 +105,7 @@ namespace gcc
 
     void generic_visitor::visit(source::program *program)
     {
-        for (const auto& constant : program->definitions())
+        for (const auto& constant : program->type_definitions)
         {
             constant->accept(this);
         }
@@ -153,7 +158,7 @@ namespace gcc
                 definition->parameters().size(), parameter_types);
         this->main_fndecl = build_fn_decl(definition->identifier().c_str(), declaration_type);
 
-        this->symbol_map.insert({ definition->identifier(), this->main_fndecl });
+        this->symbol_map->enter(definition->identifier(), source::make_info(this->main_fndecl));
 
         tree resdecl = build_decl(UNKNOWN_LOCATION, RESULT_DECL, NULL_TREE, integer_type_node);
         DECL_CONTEXT(resdecl) = this->main_fndecl;
@@ -186,6 +191,7 @@ namespace gcc
     {
         this->current_statements = alloc_stmt_list();
         this->variable_chain = tree_chain();
+        this->symbol_map = std::make_shared<source::symbol_table<tree>>(this->symbol_map);
     }
 
     tree_symbol_mapping generic_visitor::leave_scope()
@@ -194,6 +200,7 @@ namespace gcc
                 NULL_TREE, NULL_TREE, NULL_TREE);
         tree bind_expr = build3(BIND_EXPR, void_type_node, variable_chain.head(),
                 this->current_statements, new_block);
+        this->symbol_map = this->symbol_map->scope();
 
         return tree_symbol_mapping{ bind_expr, new_block };
     }
@@ -344,9 +351,9 @@ namespace gcc
         location_t definition_location = get_location(&definition->position());
         tree definition_tree = build_decl(definition_location, CONST_DECL,
                 get_identifier(definition->identifier().c_str()), integer_type_node);
-        auto result = this->symbol_map.insert({ definition->identifier(), definition_tree });
+        auto result = this->symbol_map->enter(definition->identifier(), source::make_info(definition_tree));
 
-        if (result.second)
+        if (result)
         {
             definition->body().accept(this);
 
@@ -378,9 +385,9 @@ namespace gcc
         location_t definition_location = get_location(&definition->position());
         tree definition_tree = build_decl(definition_location, TYPE_DECL,
                 get_identifier(definition->identifier().c_str()), tree_type);
-        auto result = this->symbol_map.insert({ definition->identifier(), definition_tree });
+        auto result = this->symbol_map->enter(definition->identifier(), source::make_info(definition_tree));
 
-        if (result.second)
+        if (result)
         {
             DECL_CONTEXT(definition_tree) = this->main_fndecl;
             variable_chain.append(definition_tree);
@@ -421,11 +428,11 @@ namespace gcc
             {
                 return elna_string_type_node;
             }
-            auto symbol = this->symbol_map.find(basic_type->base_name());
+            auto symbol = this->symbol_map->lookup(basic_type->base_name());
 
-            if (symbol != this->symbol_map.end())
+            if (symbol)
             {
-                return TREE_TYPE(symbol->second);
+                return TREE_TYPE(symbol->payload);
             }
             error_at(get_location(&basic_type->position()),
                     "type '%s' not declared", basic_type->base_name().c_str());
@@ -499,9 +506,9 @@ namespace gcc
         auto declaration_location = get_location(&declaration->position());
         tree declaration_tree = build_decl(declaration_location, VAR_DECL,
                 get_identifier(declaration->identifier().c_str()), declaration_type);
-        auto result = this->symbol_map.insert({ declaration->identifier(), declaration_tree });
+        auto result = this->symbol_map->enter(declaration->identifier(), source::make_info(declaration_tree));
 
-        if (result.second)
+        if (result)
         {
             DECL_CONTEXT(declaration_tree) = this->main_fndecl;
             variable_chain.append(declaration_tree);
@@ -520,9 +527,9 @@ namespace gcc
 
     void generic_visitor::visit(source::variable_expression *expression)
     {
-        auto symbol = this->symbol_map.find(expression->name());
+        auto symbol = this->symbol_map->lookup(expression->name());
 
-        if (symbol == this->symbol_map.end())
+        if (!symbol)
         {
             error_at(get_location(&expression->position()),
                     "variable '%s' not declared in the current scope",
@@ -530,7 +537,7 @@ namespace gcc
             this->current_expression = error_mark_node;
             return;
         }
-        this->current_expression = symbol->second;
+        this->current_expression = symbol->payload;
     }
 
     void generic_visitor::visit(source::array_access_expression *expression)
diff --git a/gcc/lang-specs.h b/gcc/lang-specs.h
index 624fa37..2345566 100644
--- a/gcc/lang-specs.h
+++ b/gcc/lang-specs.h
@@ -1,3 +1,6 @@
-/* gcc-src/gcc/config/lang-specs.in */
-{".elna",  "@elna", 0, 1, 0},
-{"@elna",  "elna1 %i %(cc1_options) %{!fsyntax-only:%(invoke_as)}", 0, 1, 0},
+/* gcc/gcc.cc */
+{".elna",  "@elna", nullptr, 0, 0},
+{"@elna",
+    "elna1 %{!Q:-quiet} \
+    %i %{!fsyntax-only:%(invoke_as)}",
+    nullptr, 0, 0},
diff --git a/include/elna/gcc/elna-generic.h b/include/elna/gcc/elna-generic.h
index 4b8c3c8..28a469d 100644
--- a/include/elna/gcc/elna-generic.h
+++ b/include/elna/gcc/elna-generic.h
@@ -1,6 +1,7 @@
 #pragma once
 
 #include "elna/source/ast.h"
+#include "elna/source/symbol.h"
 #include "elna/gcc/elna-tree.h"
 
 #include "config.h"
@@ -20,7 +21,7 @@ namespace gcc
     {
         tree current_statements{ NULL_TREE };
         tree current_expression{ NULL_TREE };
-        std::unordered_map<std::string, tree> symbol_map;
+        std::shared_ptr<source::symbol_table<tree>> symbol_map;
         tree main_fndecl{ NULL_TREE };
         tree_chain variable_chain;
 
@@ -31,6 +32,8 @@ namespace gcc
         tree_symbol_mapping leave_scope();
 
     public:
+        generic_visitor();
+
         void visit(source::program *program) override;
         void visit(source::procedure_definition *definition) override;
         void visit(source::call_statement *statement) override;
diff --git a/include/elna/source/ast.h b/include/elna/source/ast.h
index e090df9..cbd7ede 100644
--- a/include/elna/source/ast.h
+++ b/include/elna/source/ast.h
@@ -8,7 +8,6 @@
 #include <string>
 #include <vector>
 #include "elna/source/result.h"
-#include "elna/source/types.h"
 
 namespace elna
 {
@@ -210,7 +209,6 @@ namespace source
     {
     public:
         std::shared_ptr<operand> place;
-        std::shared_ptr<const type> data_type;
 
     protected:
         /**
@@ -596,19 +594,16 @@ namespace source
 
     class block : public node
     {
-        std::vector<definition *> m_definitions;
         statement *m_body;
 
     public:
         std::vector<definition *> value_definitions;
 
-        block(const struct position position, std::vector<definition *>&& definitions,
-                std::vector<definition *>&& value_definitions,
+        block(const struct position position, std::vector<definition *>&& value_definitions,
                 statement *body);
         virtual void accept(parser_visitor *visitor) override;
 
         statement& body();
-        std::vector<definition *>& definitions();
 
         virtual ~block() override;
     };
@@ -616,9 +611,13 @@ namespace source
     class program : public block
     {
     public:
-        program(const struct position position, std::vector<definition *>&& definitions,
+        std::vector<definition *> type_definitions;
+
+        program(const struct position position, std::vector<definition *>&& type_definitions,
                 std::vector<definition *>&& value_definitions, statement *body);
         virtual void accept(parser_visitor *visitor) override;
+
+        virtual ~program() override;
     };
 
     template<typename T>
diff --git a/include/elna/source/result.h b/include/elna/source/result.h
index ed49fb1..94789f4 100644
--- a/include/elna/source/result.h
+++ b/include/elna/source/result.h
@@ -4,7 +4,7 @@
 #pragma once
 
 #include <cstddef>
-#include "elna/source/types.h"
+#include <string>
 
 namespace elna
 {
diff --git a/include/elna/source/symbol.h b/include/elna/source/symbol.h
new file mode 100644
index 0000000..d05310f
--- /dev/null
+++ b/include/elna/source/symbol.h
@@ -0,0 +1,106 @@
+// This Source Code Form is subject to the terms of the Mozilla Public License
+// v. 2.0. If a copy of the MPL was not distributed with this file, You can
+// obtain one at http://mozilla.org/MPL/2.0/.
+#pragma once
+
+#include <cstdint>
+#include <unordered_map>
+#include <string>
+#include <memory>
+
+namespace elna
+{
+namespace source
+{
+    /**
+     * Generic language entity information.
+     */
+    template<typename T>
+    class info
+    {
+    public:
+        T payload;
+
+        info(T payload)
+            : payload(payload)
+        {
+        }
+    };
+
+    template<typename T>
+    std::shared_ptr<info<T>> make_info(T payload)
+    {
+        return std::make_shared<info<T>>(info(payload));
+    }
+
+    /**
+     * Symbol table.
+     */
+    template<typename T>
+    class symbol_table
+    {
+    public:
+        using symbol_ptr = std::shared_ptr<info<T>>;
+
+    private:
+        std::unordered_map<std::string, symbol_ptr> entries;
+        std::shared_ptr<symbol_table> outer_scope;
+
+    public:
+        /**
+         * Constructs a new symbol with an optional outer scope.
+         *
+         * \param scope Outer scope.
+         */
+        explicit symbol_table(std::shared_ptr<symbol_table> scope = nullptr)
+            : outer_scope(scope)
+        {
+        }
+
+        /**
+         * Looks for symbol in the table by name. Returns nullptr if the symbol
+         * can not be found.
+         *
+         * \param name Symbol name.
+         * \return Symbol from the table if found.
+         */
+        symbol_ptr lookup(const std::string& name)
+        {
+            auto entry = entries.find(name);
+
+            if (entry != entries.cend())
+            {
+                return entry->second;
+            }
+            if (this->outer_scope != nullptr)
+            {
+                return this->outer_scope->lookup(name);
+            }
+            return nullptr;
+        }
+
+        /**
+         * Registers new symbol.
+         *
+         * \param name Symbol name.
+         * \param entry Symbol information.
+         *
+         * \return Whether the insertion took place.
+         */
+        bool enter(const std::string& name, symbol_ptr entry)
+        {
+            return entries.insert({ name, entry }).second;
+        }
+
+        /**
+         * Returns the outer scope or nullptr if the this is the global scope.
+         *
+         * \return Outer scope.
+         */
+        std::shared_ptr<symbol_table> scope()
+        {
+            return this->outer_scope;
+        }
+    };
+}
+}
diff --git a/source/ast.cc b/source/ast.cc
index 1f2cb35..50fca7e 100644
--- a/source/ast.cc
+++ b/source/ast.cc
@@ -65,10 +65,6 @@ namespace source
 
     void empty_visitor::visit(block *block)
     {
-        for (const auto& constant : block->definitions())
-        {
-            constant->accept(this);
-        }
         for (const auto& definition : block->value_definitions)
         {
             definition->accept(this);
@@ -78,6 +74,10 @@ namespace source
 
     void empty_visitor::visit(program *program)
     {
+        for (auto definition : program->type_definitions)
+        {
+            definition->accept(this);
+        }
         visit(reinterpret_cast<block *>(program));
     }
 
@@ -447,11 +447,9 @@ namespace source
         delete m_body;
     }
 
-    block::block(const struct position position, std::vector<definition *>&& definitions,
-            std::vector<definition *>&& value_definitions,
+    block::block(const struct position position, std::vector<definition *>&& value_definitions,
             statement *body)
-        : node(position), m_definitions(std::move(definitions)),
-        m_body(std::move(body)), value_definitions(std::move(value_definitions))
+        : node(position), m_body(std::move(body)), value_definitions(std::move(value_definitions))
     {
     }
 
@@ -460,11 +458,6 @@ namespace source
         visitor->visit(this);
     }
 
-    std::vector<definition *>& block::definitions()
-    {
-        return m_definitions;
-    }
-
     statement& block::body()
     {
         return *m_body;
@@ -472,10 +465,6 @@ namespace source
 
     block::~block()
     {
-        for (auto definition : m_definitions)
-        {
-            delete definition;
-        }
         for (auto definition : value_definitions)
         {
             delete definition;
@@ -483,9 +472,11 @@ namespace source
         delete m_body;
     }
 
-    program::program(const struct position position, std::vector<definition *>&& definitions,
+    program::program(const struct position position,
+            std::vector<definition *>&& type_definitions,
             std::vector<definition *>&& value_definitions, statement *body)
-        : block(position, std::move(definitions), std::move(value_definitions), body)
+        : block(position, std::move(value_definitions), body),
+        type_definitions(std::move(type_definitions))
     {
     }
 
@@ -494,6 +485,14 @@ namespace source
         visitor->visit(this);
     }
 
+    program::~program()
+    {
+        for (auto definition : type_definitions)
+        {
+            delete definition;
+        }
+    }
+
     char_literal::char_literal(const struct position position, const unsigned char value)
         : expression(position), m_character(value)
     {
diff --git a/source/parser.yy b/source/parser.yy
index 0276bb7..60de2dc 100644
--- a/source/parser.yy
+++ b/source/parser.yy
@@ -126,8 +126,10 @@ program:
             {
                 *value_definition++ = variable;
             }
-            driver.tree = std::make_unique<elna::source::program>(elna::source::position{},
+            auto tree = new elna::source::program(elna::source::position{},
                  std::move(definitions), std::move(value_definitions), std::move($5));
+
+            driver.tree.reset(tree);
         }
 block: constant_part variable_part statement
         {
@@ -143,7 +145,7 @@ block: constant_part variable_part statement
                 *definition++ = variable;
             }
             $$ = new elna::source::block(elna::source::position{},
-                 {}, std::move(definitions), std::move($3));
+                 std::move(definitions), std::move($3));
         };
 procedure_definition:
     PROCEDURE IDENTIFIER formal_parameter_list SEMICOLON block SEMICOLON
@@ -285,7 +287,7 @@ expressions:
         }
     | expression { $$.emplace_back(std::move($1)); }
 designator_expression:
-	designator_expression LEFT_SQUARE expression RIGHT_SQUARE
+    designator_expression LEFT_SQUARE expression RIGHT_SQUARE
         {
             $$ = new elna::source::array_access_expression(elna::source::make_position(@1), $1, $3);
         }