diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5a494b5..1fadc02 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -22,7 +22,7 @@ add_executable(elna cli/main.cpp
 	source/lexer.cpp include/elna/source/lexer.hpp
 	source/parser.cpp include/elna/source/parser.hpp
 	source/result.cpp include/elna/source/result.hpp
-	source/symboltable.cpp include/elna/source/symboltable.hpp
+	source/semantic.cpp include/elna/source/semantic.hpp
 	backend/riscv.cpp include/elna/backend/riscv.hpp
 	backend/target.cpp include/elna/backend/target.hpp
 	cli/cl.cpp include/elna/cli/cl.hpp
diff --git a/TODO b/TODO
index e768a6e..d5b9dcc 100644
--- a/TODO
+++ b/TODO
@@ -5,13 +5,15 @@
 - Parser should be able to collect errors.
 - Provide position information on parse tree nodes.
 - Move constants to the symbol table, so we can check at parse time for duplicates.
-- Allow defining variables.
 - Don't pass raw pointers to the visitor methods.
-- Make error abstract and derive unexpected_token in the lex module from it.
-- Wrap the tokens in a struct with methods for incrementing and lookups.
 - While loop.
 - If condition.
-- Grouping multiple statements with begin and end (compound_statement).
+- Introduce program node which contains global state and functions.
+- Calculate additional stack space needed for subexpressions in the allocator
+  visitor and not in the backend.
+- Support immediates greater than 12 bits.
+- It seems instructions are correctly encoded only if the compiler is running
+  on a little endian architecture.
 
 # Shell
 - Persist the history.
diff --git a/backend/riscv.cpp b/backend/riscv.cpp
index ca29b83..847655c 100644
--- a/backend/riscv.cpp
+++ b/backend/riscv.cpp
@@ -63,7 +63,6 @@ namespace elna::riscv
 
     void visitor::visit(source::definition *definition)
     {
-        constants[definition->identifier()] = definition->body().number();
     }
 
     void visitor::visit(source::block *block)
@@ -73,14 +72,7 @@ namespace elna::riscv
         this->instructions.push_back(instruction(base_opcode::store));
         this->instructions.push_back(instruction(base_opcode::opImm));
 
-        for (const auto& block_definition : block->definitions())
-        {
-            block_definition->accept(this);
-        }
-        for (const auto& block_declaration : block->declarations())
-        {
-            block_declaration->accept(this);
-        }
+        table = block->table();
         block->body().accept(this);
 
         // Set the return value (0).
@@ -88,7 +80,9 @@ namespace elna::riscv
             .r(x_register::a0, funct3_t::_and, x_register::zero, x_register::zero));
 
         // Prologue.
-        const uint stack_size = static_cast<std::uint32_t>(variable_counter * 4 + 12);
+        auto main_symbol =
+            std::dynamic_pointer_cast<source::procedure_info>(table->lookup("main"));
+        const uint stack_size = static_cast<std::uint32_t>(variable_counter * 4 + 8 + main_symbol->stack_size());
 
         this->instructions[0].i(x_register::sp, funct3_t::addi, x_register::sp, -stack_size);
         this->instructions[1].s(stack_size - 4, funct3_t::sw, x_register::sp, x_register::s0);
@@ -143,18 +137,37 @@ namespace elna::riscv
         }
     }
 
-    void visitor::visit(source::assignment_statement *statement)
+    void visitor::visit(source::assign_statement *statement)
     {
+        const auto free_register = this->register_in_use ? x_register::a0 : x_register::t0;
+        auto symbol = table->lookup(statement->lvalue());
+        auto variable_symbol = std::dynamic_pointer_cast<source::variable_info>(symbol);
+
+        statement->rvalue().accept(this);
+
+        this->instructions.push_back(instruction(base_opcode::store)
+            .s(variable_symbol->offset, funct3_t::sw, x_register::s0, x_register::a0));
     }
 
     void visitor::visit(source::variable_expression *variable)
     {
         const auto free_register = this->register_in_use ? x_register::a0 : x_register::t0;
 
-        this->instructions.push_back(
-            instruction(base_opcode::opImm) // movl $x, %eax; where $x is a number.
-                .i(free_register, funct3_t::addi, x_register::zero, constants[variable->name()])
-        );
+        auto symbol = table->lookup(variable->name());
+        if (auto constant_symbol = std::dynamic_pointer_cast<source::constant_info>(symbol))
+        {
+            this->instructions.push_back(
+                instruction(base_opcode::opImm) // movl $x, %eax; where $x is a number.
+                    .i(free_register, funct3_t::addi, x_register::zero, constant_symbol->value())
+            );
+        }
+        else if (auto variable_symbol = std::dynamic_pointer_cast<source::variable_info>(symbol))
+        {
+            this->instructions.push_back(
+                instruction(base_opcode::store)
+                    .i(free_register, funct3_t::lw, x_register::s0, variable_symbol->offset)
+            );
+        }
     }
 
     void visitor::visit(source::integer_literal *number)
diff --git a/cli/cl.cpp b/cli/cl.cpp
index fe1a124..1c8b49c 100644
--- a/cli/cl.cpp
+++ b/cli/cl.cpp
@@ -1,5 +1,6 @@
 #include "elna/cli/cl.hpp"
 #include "elna/backend/target.hpp"
+#include "elna/source/semantic.hpp"
 #include <cstddef>
 #include <fstream>
 #include <sstream>
@@ -42,11 +43,13 @@ namespace elna::cli
             }
             return 1;
         }
-        auto ast = source::parser(lex_result.success()).parse();
+        auto ast = source::parser(std::move(lex_result.success())).parse();
         if (ast == nullptr)
         {
             return 2;
         }
+        source::name_analysis_visitor().visit(ast.get());
+        source::allocator_visitor().visit(ast.get());
         riscv::riscv32_elf(ast.get(), out_file);
 
         return 0;
diff --git a/include/elna/backend/riscv.hpp b/include/elna/backend/riscv.hpp
index a5b33b8..63d4f1d 100644
--- a/include/elna/backend/riscv.hpp
+++ b/include/elna/backend/riscv.hpp
@@ -1,7 +1,6 @@
 #pragma once
 
 #include <cstdint>
-#include <unordered_map>
 #include "elna/source/parser.hpp"
 
 namespace elna::riscv
@@ -163,13 +162,13 @@ namespace elna::riscv
         bool register_in_use{ true };
         std::uint32_t variable_counter = 1;
         std::vector<reference> references;
-        std::unordered_map<std::string, std::int32_t> constants;
+        std::shared_ptr<source::symbol_table> table;
 
         virtual void visit(source::declaration *declaration) override;
         virtual void visit(source::definition *definition) override;
         virtual void visit(source::bang_statement *statement) override;
         virtual void visit(source::compound_statement *statement) override;
-        virtual void visit(source::assignment_statement *statement) override;
+        virtual void visit(source::assign_statement *statement) override;
         virtual void visit(source::block *block) override;
         virtual void visit(source::variable_expression *variable) override;
         virtual void visit(source::integer_literal *number) override;
diff --git a/include/elna/source/lexer.hpp b/include/elna/source/lexer.hpp
index 4a0da00..f52bde0 100644
--- a/include/elna/source/lexer.hpp
+++ b/include/elna/source/lexer.hpp
@@ -1,6 +1,7 @@
 #pragma once
 
 #include <cstdint>
+#include <optional>
 #include <string>
 #include <vector>
 #include "elna/source/result.hpp"
@@ -128,11 +129,93 @@ namespace elna::source
         std::string what() const override;
     };
 
+    struct lexer
+    {
+        lexer(std::vector<token>&& tokens, const position last_position);
+        lexer(const lexer&) = delete;
+        lexer(lexer&&) = default;
+
+        lexer& operator=(const lexer&) = delete;
+        lexer& operator=(lexer&&) = default;
+
+        lexer& operator++();
+        const token& operator*() const;
+        const token *operator->() const;
+
+        /**
+         * This function never fails and returns \ref token::type::eof at the
+         * end of the token stream.
+         *
+         * \return Current token.
+         */
+        const token& current() const noexcept;
+
+        /**
+         * \param token_type Token type.
+         * \return Whether the current token is \a token_type.
+         */
+        bool current(const token::type token_type) const noexcept;
+
+        /**
+         * Adds an \ref unexpected_token error to the error list.
+         *
+         * \param expected The token was expected.
+         */
+        void add_error(const token& expected);
+
+        /**
+         * Expects the current token to be \a token_type. In this case returns
+         * this token and advances to the next token in the stream.
+         *
+         * \param token_type Expected token type.
+         * \return Current token.
+         */
+        std::optional<std::reference_wrapper<const token>> advance(const token::type token_type);
+
+        /**
+         * Returns that follows the current token. If the current token is
+         * \ref token::type::eof, returns it.
+         *
+         * \return The token that follows the current one.
+         */
+        const token& look_ahead() const;
+
+        /**
+         * Tells whether the token following the current one is \a token_type.
+         *
+         * \param token_type Token type.
+         * \return Whether the next token is \a token_type.
+         */
+        bool look_ahead(const token::type token_type) const;
+
+        /**
+         * Skips one token if it is of type \a token_type. Adds an
+         * \ref unexpected_token error otherwise.
+         *
+         * \param token_type The token type was expected.
+         * \return Whether the current token was \a token_type.
+         */
+        bool skip(const token::type token_type);
+
+        /**
+         * Gets produced errors.
+         *
+         * \return Produced error list.
+         */
+        const std::list<std::unique_ptr<error>>& errors() const noexcept;
+
+    private:
+        std::vector<token> tokens;
+        std::vector<token>::const_iterator iterator;
+        std::list<std::unique_ptr<error>> m_errors;
+        token eof;
+    };
+
     /**
-     * Split the source into tokens.
+     * Splits the source text into tokens.
      *
      * \param buffer Source text.
      * \return Tokens or error.
      */
-    elna::source::result<std::vector<token>> lex(const std::string& buffer);
+    elna::source::result<lexer> lex(const std::string& buffer);
 }
diff --git a/include/elna/source/parser.hpp b/include/elna/source/parser.hpp
index b61cf00..1d63c70 100644
--- a/include/elna/source/parser.hpp
+++ b/include/elna/source/parser.hpp
@@ -1,9 +1,7 @@
 #pragma once
 
 #include <boost/core/noncopyable.hpp>
-#include <cstdint>
 #include <memory>
-#include <optional>
 #include <elna/source/lexer.hpp>
 
 namespace elna::source
@@ -20,7 +18,7 @@ namespace elna::source
     class definition;
     class bang_statement;
     class compound_statement;
-    class assignment_statement;
+    class assign_statement;
     class block;
     class binary_expression;
     class variable_expression;
@@ -32,13 +30,26 @@ namespace elna::source
         virtual void visit(definition *) = 0;
         virtual void visit(bang_statement *) = 0;
         virtual void visit(compound_statement *) = 0;
-        virtual void visit(assignment_statement *) = 0;
+        virtual void visit(assign_statement *) = 0;
         virtual void visit(block *) = 0;
         virtual void visit(binary_expression *) = 0;
         virtual void visit(variable_expression *) = 0;
         virtual void visit(integer_literal *) = 0;
     };
 
+    struct empty_visitor : parser_visitor
+    {
+        virtual void visit(declaration *declaration) override;
+        virtual void visit(definition *definition) override;
+        virtual void visit(bang_statement *statement) override;
+        virtual void visit(compound_statement *statement) override;
+        virtual void visit(assign_statement *statement) override;
+        virtual void visit(block *block) override;
+        virtual void visit(binary_expression *expression) override;
+        virtual void visit(variable_expression *variable) override;
+        virtual void visit(integer_literal *number) override;
+    };
+
     /**
      * AST node.
      */
@@ -109,11 +120,17 @@ namespace elna::source
         std::vector<std::unique_ptr<statement>>& statements();
     };
 
-    class assignment_statement : public statement
+    class assign_statement : public statement
     {
-        std::unique_ptr<variable_expression> lvalue;
-        std::unique_ptr<expression> rvalue;
+        std::string m_lvalue;
+        std::unique_ptr<expression> m_rvalue;
+
+    public:
+        assign_statement(const std::string& lvalue, std::unique_ptr<expression>&& rvalue);
         virtual void accept(parser_visitor *visitor) override;
+
+        std::string& lvalue() noexcept;
+        expression& rvalue();
     };
 
     /**
@@ -124,6 +141,7 @@ namespace elna::source
         std::unique_ptr<statement> m_body;
         std::vector<std::unique_ptr<definition>> m_definitions;
         std::vector<std::unique_ptr<declaration>> m_declarations;
+        std::shared_ptr<symbol_table> m_table;
 
     public:
         block(std::vector<std::unique_ptr<definition>>&& definitions,
@@ -134,6 +152,7 @@ namespace elna::source
         statement& body();
         std::vector<std::unique_ptr<definition>>& definitions() noexcept;
         std::vector<std::unique_ptr<declaration>>& declarations() noexcept;
+        std::shared_ptr<symbol_table> table();
     };
 
     class integer_literal : public expression
@@ -174,13 +193,8 @@ namespace elna::source
         binary_operator operation() const noexcept;
     };
 
-    struct parser : boost::noncopyable
+    class parser : boost::noncopyable
     {
-        parser(const std::vector<token>& tokens);
-
-        std::unique_ptr<block> parse();
-
-    private:
         std::unique_ptr<expression> parse_factor();
         std::unique_ptr<expression> parse_term();
         std::unique_ptr<expression> parse_expression();
@@ -189,15 +203,28 @@ namespace elna::source
         std::unique_ptr<statement> parse_statement();
         std::unique_ptr<bang_statement> parse_bang_statement();
         std::unique_ptr<compound_statement> parse_compound_statement();
+        std::unique_ptr<assign_statement> parse_assign_statement();
         std::vector<std::unique_ptr<definition>> parse_definitions();
         std::vector<std::unique_ptr<declaration>> parse_declarations();
         std::unique_ptr<block> parse_block();
 
-        std::optional<std::reference_wrapper<const token>> advance(const token::type token_type);
-        bool skip(const token::type token_type);
+        lexer iterator;
 
-        std::vector<token>::const_iterator tokens;
-        std::vector<token>::const_iterator end;
-        std::list<std::unique_ptr<error>> errors;
+    public:
+        parser(lexer&& tokens);
+
+        /**
+         * Parses a source text.
+         *
+         * \return Parsed program or nothing if an error occurred.
+         */
+        std::unique_ptr<block> parse();
+
+        /**
+         * Gets produced errors.
+         *
+         * \return Produced error list.
+         */
+        const std::list<std::unique_ptr<error>>& errors() const noexcept;
     };
 }
diff --git a/include/elna/source/result.hpp b/include/elna/source/result.hpp
index a0ea7b9..8cb3513 100644
--- a/include/elna/source/result.hpp
+++ b/include/elna/source/result.hpp
@@ -1,10 +1,13 @@
 #pragma once
 
 #include <cstddef>
+#include <cstdint>
 #include <variant>
 #include <list>
 #include <memory>
+#include <string>
 #include <type_traits>
+#include <unordered_map>
 
 namespace elna::source
 {
@@ -50,8 +53,8 @@ namespace elna::source
         using E = std::list<std::unique_ptr<source::error>>;
 
         template<typename... Args, typename = std::enable_if<std::is_constructible_v<T, Args...>>>
-        explicit result(Args&&... arguments)
-            : payload(std::forward<Args>(arguments)...)
+        explicit result(std::in_place_t, Args&&... arguments)
+            : payload(std::in_place_type<T>, std::forward<Args>(arguments)...)
         {
         }
 
@@ -62,6 +65,7 @@ namespace elna::source
 
         template<typename U, typename = std::enable_if<std::is_base_of_v<error, U>>>
         explicit result(U&& first)
+            : payload(E())
         {
             errors().emplace_back(std::make_unique<U>(first));
         }
@@ -89,4 +93,75 @@ namespace elna::source
     private:
         std::variant<T, E> payload;
     };
+
+    class name_collision final : public error
+    {
+        position previous;
+        std::string name;
+
+    public:
+        name_collision(const std::string& name, const position current, const position previous);
+
+        std::string what() const override;
+    };
+
+    /**
+     * Generic language entity information.
+     */
+    class info
+    {
+    public:
+        virtual ~info() = 0;
+
+    protected:
+        info();
+    };
+
+    /**
+     * Constant information.
+     */
+    class constant_info final : public info
+    {
+        std::int32_t m_value;
+
+    public:
+        constant_info(const std::int32_t value);
+        ~constant_info() override;
+        std::int32_t value() const noexcept;
+    };
+
+    /**
+     * Variable information.
+     */
+    struct variable_info final : public info
+    {
+        std::ptrdiff_t offset{ 0 };
+
+        ~variable_info() override;
+    };
+
+    class procedure_info final : public info
+    {
+        std::size_t local_stack_size{ 0 };
+
+    public:
+        ~procedure_info() override;
+
+        void stack_size(const std::size_t size) noexcept;
+        std::size_t stack_size() const noexcept;
+    };
+
+    /**
+     * Symbol table.
+     */
+    class symbol_table
+    {
+        std::unordered_map<std::string, std::shared_ptr<info>> entries;
+
+    public:
+        symbol_table() = default;
+
+        std::shared_ptr<info> lookup(const std::string& name);
+        void enter(const std::string& name, std::shared_ptr<info> entry);
+    };
 }
diff --git a/include/elna/source/semantic.hpp b/include/elna/source/semantic.hpp
new file mode 100644
index 0000000..6d2e311
--- /dev/null
+++ b/include/elna/source/semantic.hpp
@@ -0,0 +1,25 @@
+#pragma once
+
+#include "elna/source/parser.hpp"
+
+namespace elna::source
+{
+    class name_analysis_visitor final : public empty_visitor
+    {
+        std::shared_ptr<symbol_table> table;
+
+    public:
+        void visit(definition *definition) override;
+        void visit(declaration *declaration) override;
+        void visit(block *block) override;
+    };
+
+    class allocator_visitor final : public empty_visitor
+    {
+        std::ptrdiff_t offset;
+
+    public:
+        void visit(declaration *declaration) override;
+        void visit(block *block) override;
+    };
+}
diff --git a/include/elna/source/symboltable.hpp b/include/elna/source/symboltable.hpp
deleted file mode 100644
index a5a59b3..0000000
--- a/include/elna/source/symboltable.hpp
+++ /dev/null
@@ -1,73 +0,0 @@
-#pragma once
-
-#include "elna/source/parser.hpp"
-#include <unordered_map>
-#include <memory>
-
-namespace elna::source
-{
-    class name_collision final : public error
-    {
-        position previous;
-        std::string name;
-
-    public:
-        name_collision(const std::string& name, const position current, const position previous);
-
-        std::string what() const override;
-    };
-
-    class info
-    {
-    public:
-        virtual ~info() = 0;
-
-    protected:
-        info();
-    };
-
-    class constant_info final : public info
-    {
-        std::int32_t m_value;
-
-    public:
-        constant_info(const std::int32_t value);
-        ~constant_info() override;
-        std::int32_t value() const noexcept;
-    };
-
-    class variable_info final : public info
-    {
-        std::size_t m_offset{ 0 };
-
-    public:
-        variable_info(const std::size_t offset);
-        ~variable_info() override;
-
-        std::size_t offset() const noexcept;
-    };
-
-    class symbol_table
-    {
-        std::unordered_map<std::string, std::shared_ptr<info>> entries;
-
-    public:
-        symbol_table() = default;
-
-        std::shared_ptr<info> lookup(const std::string& name);
-        void enter(const std::string& name, std::shared_ptr<info> entry);
-    };
-
-    class name_analysis_visitor final : public source::parser_visitor
-    {
-        void visit(declaration *declaration) override;
-        void visit(definition *definition) override;
-        void visit(bang_statement *statement) override;
-        void visit(compound_statement *statement) override;
-        void visit(assignment_statement *statement) override;
-        void visit(block *block) override;
-        void visit(integer_literal *number) override;
-        void visit(variable_expression *variable) override;
-        void visit(binary_expression *expression) override;
-    };
-}
diff --git a/include/elna/tester.hpp b/include/elna/tester.hpp
index ee34351..1690a33 100644
--- a/include/elna/tester.hpp
+++ b/include/elna/tester.hpp
@@ -1,9 +1,28 @@
 #pragma once
 
 #include <cstdint>
+#include <string>
+#include <filesystem>
+
+#define BOOST_PROCESS_USE_STD_FS
 
 namespace elna
 {
+    enum class test_status
+    {
+        successful,
+        compile_failed,
+        build_failed,
+        expectation_failed,
+    };
+
+    struct test_result final
+    {
+        test_status status{ test_status::successful };
+        int code{ 0 };
+        std::string output;
+    };
+
     class test_results final
     {
         std::uint32_t m_total{ 0 };
@@ -17,6 +36,8 @@ namespace elna
         std::uint32_t failed() const noexcept;
 
         int exit_code() const noexcept;
-        void add_exit_code(const int exit_code) noexcept;
+        void add_exit_code(const test_status result) noexcept;
     };
+
+    void print_result(const std::filesystem::directory_entry& test_entry, const test_result& result);
 }
diff --git a/source/lexer.cpp b/source/lexer.cpp
index 95f193e..d509273 100644
--- a/source/lexer.cpp
+++ b/source/lexer.cpp
@@ -6,7 +6,6 @@ namespace elna::source
 {
     using source_position = elna::source::position;
     using source_error = elna::source::error;
-    using source_result = elna::source::result<std::vector<token>>;
 
     std::pair<text_iterator, text_iterator> text_iterators(const std::string &buffer)
     {
@@ -225,7 +224,83 @@ namespace elna::source
         return "Unexpected token";
     }
 
-    source_result lex(const std::string& buffer)
+    lexer::lexer(std::vector<token>&& tokens, const position last_position)
+        : tokens(std::move(tokens)), iterator(this->tokens.cbegin()), eof(token(token::type::eof, last_position))
+    {
+    }
+
+    lexer& lexer::operator++()
+    {
+        ++iterator;
+        return *this;
+    }
+
+    const token& lexer::operator*() const
+    {
+        return *iterator;
+    }
+
+    const token *lexer::operator->() const
+    {
+        return iterator.base();
+    }
+
+    const token& lexer::current() const noexcept
+    {
+        if (iterator == tokens.cend())
+        {
+            return this->eof;
+        }
+        return *iterator;
+    }
+
+    bool lexer::current(const token::type token_type) const noexcept
+    {
+        return current().of() == token_type;
+    }
+
+    void lexer::add_error(const token& expected)
+    {
+        m_errors.push_back(std::make_unique<unexpected_token>(expected));
+    }
+
+    std::optional<std::reference_wrapper<const token>> lexer::advance(const token::type token_type)
+    {
+        if (iterator != tokens.cend() && iterator->of() == token_type)
+        {
+            return std::make_optional<>(std::cref(*iterator++));
+        }
+        add_error(current());
+        return std::optional<std::reference_wrapper<const token>>();
+    }
+
+    const token& lexer::look_ahead() const
+    {
+        auto tmp = iterator;
+        ++tmp;
+        if (iterator == tokens.cend() || tmp == tokens.cend())
+        {
+            return eof;
+        }
+        return *tmp;
+    }
+
+    bool lexer::look_ahead(const token::type token_type) const
+    {
+        return look_ahead().of() == token_type;
+    }
+
+    bool lexer::skip(const token::type token_type)
+    {
+        return advance(token_type).has_value();
+    }
+
+    const std::list<std::unique_ptr<error>>& lexer::errors() const noexcept
+    {
+        return m_errors;
+    }
+
+    result<lexer> lex(const std::string& buffer)
     {
         std::vector<token> tokens;
         auto [iterator, text_end] = text_iterators(buffer);
@@ -322,12 +397,10 @@ namespace elna::source
             }
             else
             {
-                return source_result(unexpected_character{ std::string{ *iterator }, iterator.position() });
+                return result<lexer>(unexpected_character{ std::string{ *iterator }, iterator.position() });
             }
             ++iterator;
         }
-        tokens.push_back(token(token::type::eof, iterator.position()));
-
-        return source_result(std::move(tokens));
+        return result<lexer>(std::in_place, std::move(tokens), iterator.position());
     }
 }
diff --git a/source/parser.cpp b/source/parser.cpp
index 5a58501..77f20bb 100644
--- a/source/parser.cpp
+++ b/source/parser.cpp
@@ -3,6 +3,60 @@
 
 namespace elna::source
 {
+    void empty_visitor::visit(declaration *declaration)
+    {
+    }
+
+    void empty_visitor::visit(definition *definition)
+    {
+        definition->body().accept(this);
+    }
+
+    void empty_visitor::visit(bang_statement *statement)
+    {
+        statement->body().accept(this);
+    }
+
+    void empty_visitor::visit(compound_statement *statement)
+    {
+        for (auto& nested_statement : statement->statements())
+        {
+            nested_statement->accept(this);
+        }
+    }
+
+    void empty_visitor::visit(assign_statement *statement)
+    {
+        statement->rvalue().accept(this);
+    }
+
+    void empty_visitor::visit(block *block)
+    {
+        for (const auto& block_definition : block->definitions())
+        {
+            block_definition->accept(this);
+        }
+        for (const auto& block_declaration : block->declarations())
+        {
+            block_declaration->accept(this);
+        }
+        block->body().accept(this);
+    }
+
+    void empty_visitor::visit(binary_expression *expression)
+    {
+        expression->lhs().accept(this);
+        expression->rhs().accept(this);
+    }
+
+    void empty_visitor::visit(variable_expression *variable)
+    {
+    }
+
+    void empty_visitor::visit(integer_literal *number)
+    {
+    }
+
     /**
      * AST node.
      */
@@ -48,7 +102,9 @@ namespace elna::source
     block::block(std::vector<std::unique_ptr<definition>>&& definitions,
             std::vector<std::unique_ptr<declaration>>&& declarations,
             std::unique_ptr<statement>&& body)
-        : m_definitions(std::move(definitions)), m_declarations(std::move(declarations)), m_body(std::move(body))
+        : m_definitions(std::move(definitions)),
+        m_declarations(std::move(declarations)), m_body(std::move(body)),
+        m_table(std::make_shared<symbol_table>())
     {
     }
 
@@ -72,6 +128,11 @@ namespace elna::source
         return m_declarations;
     }
 
+    std::shared_ptr<symbol_table> block::table()
+    {
+        return m_table;
+    }
+
     integer_literal::integer_literal(const std::int32_t value)
         : m_number(value)
     {
@@ -175,13 +236,28 @@ namespace elna::source
         return m_statements;
     }
 
-    void assignment_statement::accept(parser_visitor *visitor)
+    void assign_statement::accept(parser_visitor *visitor)
     {
         visitor->visit(this);
     }
 
-    parser::parser(const std::vector<token>& tokens)
-        : tokens(tokens.cbegin()), end(tokens.cend())
+    assign_statement::assign_statement(const std::string& lvalue, std::unique_ptr<expression>&& rvalue)
+        : m_lvalue(lvalue), m_rvalue(std::move(rvalue))
+    {
+    }
+
+    std::string& assign_statement::lvalue() noexcept
+    {
+        return m_lvalue;
+    }
+
+    expression& assign_statement::rvalue()
+    {
+        return *m_rvalue;
+    }
+
+    parser::parser(lexer&& tokens)
+        : iterator(std::move(tokens))
     {
     }
 
@@ -190,27 +266,32 @@ namespace elna::source
         return parse_block();
     }
 
+    const std::list<std::unique_ptr<error>>& parser::errors() const noexcept
+    {
+        return iterator.errors();
+    }
+
     std::unique_ptr<expression> parser::parse_factor()
     {
-        if (tokens->of() == source::token::type::identifier)
+        if (iterator->of() == source::token::type::identifier)
         {
-            auto result = std::make_unique<variable_expression>(tokens->identifier());
-            ++tokens;
+            auto result = std::make_unique<variable_expression>(iterator->identifier());
+            ++iterator;
             return result;
         }
-        else if (tokens->of() == source::token::token::type::number)
+        else if (iterator->of() == source::token::token::type::number)
         {
-            auto result = std::make_unique<integer_literal>(tokens->number());
-            ++tokens;
+            auto result = std::make_unique<integer_literal>(iterator->number());
+            ++iterator;
             return result;
         }
-        else if (tokens->of() == source::token::type::left_paren)
+        else if (iterator->of() == source::token::type::left_paren)
         {
-            ++tokens;
+            ++iterator;
 
             auto expression = parse_expression();
 
-            ++tokens;
+            ++iterator;
 
             return expression;
         }
@@ -220,14 +301,14 @@ namespace elna::source
     std::unique_ptr<expression> parser::parse_term()
     {
         auto lhs = parse_factor();
-        if (lhs == nullptr || tokens == end || tokens->of() != source::token::type::factor_operator)
+        if (lhs == nullptr || iterator.current().of() != source::token::type::factor_operator)
         {
             return lhs;
         }
-        while (tokens->of() == source::token::type::factor_operator)
+        while (iterator->of() == source::token::type::factor_operator)
         {
-            auto _operator = tokens->identifier()[0];
-            ++tokens;
+            auto _operator = iterator->identifier()[0];
+            ++iterator;
 
             auto rhs = parse_factor();
             lhs = std::make_unique<binary_expression>(std::move(lhs),
@@ -239,14 +320,14 @@ namespace elna::source
     std::unique_ptr<expression> parser::parse_expression()
     {
         auto term = parse_term();
-        if (term == nullptr || tokens == end || tokens->of() != source::token::type::term_operator)
+        if (term == nullptr || iterator.current().of() != source::token::type::term_operator)
         {
             return term;
         }
-        while (tokens->of() == source::token::type::term_operator)
+        while (iterator->of() == source::token::type::term_operator)
         {
-            auto _operator = tokens->identifier()[0];
-            ++tokens;
+            auto _operator = iterator->identifier()[0];
+            ++iterator;
 
             auto rhs = parse_term();
             term = std::make_unique<binary_expression>(std::move(term),
@@ -257,22 +338,22 @@ namespace elna::source
 
     std::unique_ptr<definition> parser::parse_definition()
     {
-        auto definition_identifier = advance(token::type::identifier);
+        auto definition_identifier = iterator.advance(token::type::identifier);
 
         if (!definition_identifier.has_value())
         {
             return nullptr;
         }
-        if (!skip(token::type::equals))
+        if (!iterator.skip(token::type::equals))
         {
             return nullptr;
         }
 
-        if (tokens->of() == source::token::type::number)
+        if (iterator->of() == source::token::type::number)
         {
             auto result = std::make_unique<definition>(definition_identifier.value().get().identifier(),
-                    std::make_unique<integer_literal>(tokens->number()));
-            ++tokens;
+                    std::make_unique<integer_literal>(iterator->number()));
+            ++iterator;
             return result;
         }
         return nullptr;
@@ -280,7 +361,7 @@ namespace elna::source
 
     std::unique_ptr<declaration> parser::parse_declaration()
     {
-        auto declaration_identifier = advance(token::type::identifier);
+        auto declaration_identifier = iterator.advance(token::type::identifier);
 
         if (!declaration_identifier.has_value())
         {
@@ -291,21 +372,25 @@ namespace elna::source
 
     std::unique_ptr<statement> parser::parse_statement()
     {
-        if (tokens->of() == source::token::type::bang)
+        if (iterator.look_ahead(token::type::assignment))
+        {
+            return parse_assign_statement();
+        }
+        else if (iterator.current(token::type::bang))
         {
             return parse_bang_statement();
         }
-        else if (tokens->of() == source::token::type::begin)
+        else if (iterator.current(token::type::begin))
         {
             return parse_compound_statement();
         }
-        errors.push_back(std::make_unique<unexpected_token>(unexpected_token{ *tokens }));
+        iterator.add_error(*iterator);
         return nullptr;
     }
 
     std::unique_ptr<bang_statement> parser::parse_bang_statement()
     {
-        if (!advance(token::type::bang))
+        if (!iterator.advance(token::type::bang))
         {
             return nullptr;
         }
@@ -321,7 +406,7 @@ namespace elna::source
 
     std::unique_ptr<compound_statement> parser::parse_compound_statement()
     {
-        if (!advance(token::type::begin))
+        if (!iterator.advance(token::type::begin))
         {
             return nullptr;
         }
@@ -332,18 +417,18 @@ namespace elna::source
         {
             result->statements().push_back(std::move(next_statement));
 
-            if (tokens->of() == token::type::semicolon)
+            if (iterator->of() == token::type::semicolon)
             {
-                ++tokens;
+                ++iterator;
             }
-            else if (tokens->of() == token::type::end)
+            else if (iterator->of() == token::type::end)
             {
-                ++tokens;
+                ++iterator;
                 break;
             }
             else
             {
-                errors.push_back(std::make_unique<unexpected_token>(*tokens));
+                iterator.add_error(*iterator);
                 break;
             }
         }
@@ -351,33 +436,49 @@ namespace elna::source
         return result;
     }
 
+    std::unique_ptr<assign_statement> parser::parse_assign_statement()
+    {
+        auto name = iterator.advance(token::type::identifier);
+        if (!name.has_value() || !iterator.skip(token::type::assignment))
+        {
+            return nullptr;
+        }
+        auto rvalue = parse_expression();
+
+        if (rvalue == nullptr)
+        {
+            return nullptr;
+        }
+        return std::make_unique<assign_statement>(name.value().get().identifier(), std::move(rvalue));
+    }
+
     std::vector<std::unique_ptr<definition>> parser::parse_definitions()
     {
         std::vector<std::unique_ptr<definition>> definitions;
 
-        if (tokens->of() != token::type::let)
+        if (iterator->of() != token::type::let)
         {
             return definitions;
         }
-        ++tokens; // Skip const.
+        ++iterator; // Skip const.
 
         std::unique_ptr<definition> parsed_definition;
         while ((parsed_definition = parse_definition()) != nullptr)
         {
             definitions.push_back(std::move(parsed_definition));
 
-            if (tokens->of() == source::token::type::comma)
+            if (iterator->of() == source::token::type::comma)
             {
-                ++tokens;
+                ++iterator;
             }
-            else if (tokens->of() == source::token::type::semicolon)
+            else if (iterator->of() == source::token::type::semicolon)
             {
-                ++tokens;
+                ++iterator;
                 break;
             }
             else
             {
-                errors.push_back(std::make_unique<unexpected_token>(*tokens));
+                iterator.add_error(*iterator);
                 break;
             }
         }
@@ -388,29 +489,29 @@ namespace elna::source
     {
         std::vector<std::unique_ptr<declaration>> declarations;
 
-        if (tokens->of() != token::type::var)
+        if (iterator->of() != token::type::var)
         {
             return declarations;
         }
-        ++tokens; // Skip var.
+        ++iterator; // Skip var.
 
         std::unique_ptr<declaration> parsed_declaration;
         while ((parsed_declaration = parse_declaration()) != nullptr)
         {
             declarations.push_back(std::move(parsed_declaration));
 
-            if (tokens->of() == token::type::comma)
+            if (iterator->of() == token::type::comma)
             {
-                ++tokens;
+                ++iterator;
             }
-            else if (tokens->of() == token::type::semicolon)
+            else if (iterator->of() == token::type::semicolon)
             {
-                ++tokens;
+                ++iterator;
                 break;
             }
             else
             {
-                errors.push_back(std::make_unique<unexpected_token>(*tokens));
+                iterator.add_error(*iterator);
                 break;
             }
         }
@@ -430,25 +531,4 @@ namespace elna::source
         return std::make_unique<block>(std::move(definitions),
                 std::move(declarations), std::move(parsed_statement));
     }
-
-    std::optional<std::reference_wrapper<const token>> parser::advance(const token::type token_type)
-    {
-        if (tokens->of() == token_type)
-        {
-            return std::make_optional<>(std::cref(*tokens++));
-        }
-        errors.push_back(std::make_unique<unexpected_token>(*tokens));
-        return std::optional<std::reference_wrapper<const token>>();
-    }
-
-    bool parser::skip(const token::type token_type)
-    {
-        if (tokens->of() == token_type)
-        {
-            ++tokens;
-            return true;
-        }
-        errors.push_back(std::make_unique<unexpected_token>(*tokens));
-        return false;
-    }
 }
diff --git a/source/result.cpp b/source/result.cpp
index 42f53fe..0d989d1 100644
--- a/source/result.cpp
+++ b/source/result.cpp
@@ -16,4 +16,72 @@ namespace elna::source
     {
         return this->m_position.column;
     }
+
+    name_collision::name_collision(const std::string& name, const position current, const position previous)
+        : error(current), name(name), previous(previous)
+    {
+    }
+
+    std::string name_collision::what() const
+    {
+        return "Name '" + name + "' was already defined";
+    }
+
+    std::shared_ptr<info> symbol_table::lookup(const std::string& name)
+    {
+        auto entry = entries.find(name);
+        if (entry == entries.cend())
+        {
+            return nullptr;
+        }
+        else
+        {
+            return entry->second;
+        }
+    }
+
+    void symbol_table::enter(const std::string& name, std::shared_ptr<info> entry)
+    {
+        entries.insert_or_assign(name, entry);
+    }
+
+    info::~info()
+    {
+    }
+
+    info::info()
+    {
+    }
+
+    constant_info::constant_info(const std::int32_t value)
+        : m_value(value)
+    {
+    }
+
+    constant_info::~constant_info()
+    {
+    }
+
+    std::int32_t constant_info::value() const noexcept
+    {
+        return m_value;
+    }
+
+    variable_info::~variable_info()
+    {
+    }
+
+    procedure_info::~procedure_info()
+    {
+    }
+
+    std::size_t procedure_info::stack_size() const noexcept
+    {
+        return this->local_stack_size;
+    }
+
+    void procedure_info::stack_size(const std::size_t size) noexcept
+    {
+        this->local_stack_size = size;
+    }
 }
diff --git a/source/semantic.cpp b/source/semantic.cpp
new file mode 100644
index 0000000..bd0eb94
--- /dev/null
+++ b/source/semantic.cpp
@@ -0,0 +1,38 @@
+#include "elna/source/semantic.hpp"
+#include <cstdlib>
+
+namespace elna::source
+{
+    void name_analysis_visitor::visit(definition *definition)
+    {
+        this->table->enter(definition->identifier(),
+                std::make_shared<constant_info>(constant_info(definition->body().number())));
+    }
+
+    void name_analysis_visitor::visit(declaration *declaration)
+    {
+        this->table->enter(declaration->identifier(),
+                std::make_shared<variable_info>(variable_info()));
+    }
+
+    void name_analysis_visitor::visit(block *block)
+    {
+        this->table = block->table();
+        empty_visitor::visit(block);
+        this->table->enter("main",
+                std::make_shared<procedure_info>());
+    }
+
+    void allocator_visitor::visit(declaration *declaration)
+    {
+        this->offset -= sizeof(std::int32_t);
+    }
+
+    void allocator_visitor::visit(block *block)
+    {
+        this->offset = 0;
+        empty_visitor::visit(block);
+        std::dynamic_pointer_cast<procedure_info>(block->table()->lookup("main"))
+            ->stack_size(std::abs(this->offset));
+    }
+}
diff --git a/source/symboltable.cpp b/source/symboltable.cpp
deleted file mode 100644
index ee3b710..0000000
--- a/source/symboltable.cpp
+++ /dev/null
@@ -1,104 +0,0 @@
-#include "elna/source/symboltable.hpp"
-
-namespace elna::source
-{
-    name_collision::name_collision(const std::string& name, const position current, const position previous)
-        : error(current), name(name), previous(previous)
-    {
-    }
-
-    std::string name_collision::what() const
-    {
-        return "Name '" + name + "' was already defined";
-    }
-
-    std::shared_ptr<info> symbol_table::lookup(const std::string& name)
-    {
-        auto entry = entries.find(name);
-        if (entry == entries.cend())
-        {
-            return nullptr;
-        }
-        else
-        {
-            return entry->second;
-        }
-    }
-
-    void symbol_table::enter(const std::string& name, std::shared_ptr<info> entry)
-    {
-        entries.insert_or_assign(name, entry);
-    }
-
-    info::~info()
-    {
-    }
-
-    info::info()
-    {
-    }
-
-    constant_info::constant_info(const std::int32_t value)
-        : m_value(value)
-    {
-    }
-
-    constant_info::~constant_info()
-    {
-    }
-
-    std::int32_t constant_info::value() const noexcept
-    {
-        return m_value;
-    }
-
-    variable_info::variable_info(std::size_t offset)
-        : m_offset(offset)
-    {
-    }
-
-    variable_info::~variable_info()
-    {
-    }
-
-    std::size_t variable_info::offset() const noexcept
-    {
-        return m_offset;
-    }
-
-    void name_analysis_visitor::visit(declaration *declaration)
-    {
-    }
-
-    void name_analysis_visitor::visit(definition *definition)
-    {
-    }
-
-    void name_analysis_visitor::visit(bang_statement *statement)
-    {
-    }
-
-    void name_analysis_visitor::visit(compound_statement *statement)
-    {
-    }
-
-    void name_analysis_visitor::visit(assignment_statement *statement)
-    {
-    }
-
-    void name_analysis_visitor::visit(block *block)
-    {
-    }
-
-    void name_analysis_visitor::visit(integer_literal *number)
-    {
-    }
-
-    void name_analysis_visitor::visit(variable_expression *variable)
-    {
-    }
-
-    void name_analysis_visitor::visit(binary_expression *expression)
-    {
-    }
-}
diff --git a/tests/declare_variable.eln b/tests/declare_variable.eln
index 4f7131f..4d2d89b 100644
--- a/tests/declare_variable.eln
+++ b/tests/declare_variable.eln
@@ -1,5 +1,5 @@
 var x;
 begin
   x := 5;
-  ! 5
+  ! x
 end.
diff --git a/tests/tester.cpp b/tests/tester.cpp
index bd9eadf..2c54ade 100755
--- a/tests/tester.cpp
+++ b/tests/tester.cpp
@@ -1,9 +1,11 @@
-#include <boost/process.hpp>
-
-#include <filesystem>
-#include <iostream>
 #include "elna/tester.hpp"
 
+#include <future>
+#include <iostream>
+
+#include <boost/process.hpp>
+#include <boost/asio.hpp>
+
 namespace elna
 {
     std::uint32_t test_results::total() const noexcept
@@ -26,10 +28,10 @@ namespace elna
         return m_total == m_passed ? EXIT_SUCCESS : EXIT_FAILURE;
     }
 
-    void test_results::add_exit_code(const int exit_code) noexcept
+    void test_results::add_exit_code(const test_status status) noexcept
     {
         ++m_total;
-        if (exit_code == 0)
+        if (status == test_status::successful)
         {
             ++m_passed;
         }
@@ -45,7 +47,7 @@ namespace elna
         return in_build_directory() / path;
     }
 
-    static int build_test(const std::filesystem::directory_entry& test_entry)
+    static test_result build_test(const std::filesystem::directory_entry& test_entry)
     {
         const std::filesystem::path test_filename = test_entry.path().filename();
 
@@ -61,7 +63,7 @@ namespace elna
                 "-o", test_object.string(), test_entry.path().string());
         if (status != 0)
         {
-            return status;
+            return test_result{ test_status::compile_failed, status };
         }
         status = boost::process::system(
                 "/opt/riscv/bin/riscv32-unknown-elf-ld",
@@ -74,37 +76,55 @@ namespace elna
                 "--start-group", "-lgcc", "-lc", "-lgloss", "--end-group",
                 "/opt/riscv/lib/gcc/riscv32-unknown-elf/13.2.0/crtend.o"
         );
-        return status;
+        return test_result{};
     }
 
-    static int run_test(const std::filesystem::directory_entry& test_entry)
+    static test_result check_expectation(const std::filesystem::directory_entry& test_entry, const test_result& run)
+    {
+        const std::filesystem::path test_filename = test_entry.path().filename();
+
+        std::filesystem::path expectation_path = test_entry.path().parent_path() / "expectations" / test_filename;
+        expectation_path.replace_extension(".txt");
+
+        boost::process::opstream pipe_stream;
+        boost::process::child diff(
+                boost::process::search_path("diff"), "-Nur", "--color",
+                expectation_path.string(), "-",
+                boost::process::std_in < pipe_stream
+        );
+
+        pipe_stream << run.output;
+        pipe_stream.flush();
+        pipe_stream.pipe().close();
+        diff.wait();
+
+        if (diff.exit_code() == 0)
+        {
+            return run;
+        }
+        return test_result{ test_status::expectation_failed, run.code, run.output };
+    }
+
+    static test_result run_test(const std::filesystem::directory_entry& test_entry)
     {
         const std::filesystem::path test_filename = test_entry.path().filename();
 
         std::filesystem::path test_binary = in_build_directory(test_filename);
         test_binary.replace_extension();
 
-        std::filesystem::path expectation_path = test_entry.path().parent_path() / "expectations" / test_filename;
-        expectation_path.replace_extension(".txt");
-
-        std::cout << "Running " << test_binary << std::endl;
-
-        boost::process::pipe pipe_stream;
-        boost::process::child vm(
+        boost::asio::io_service io_service;
+        std::future<std::string> buffer;
+        boost::process::child spike(
             "/opt/riscv/bin/spike", "--isa=RV32IMAC",
             "/opt/riscv/riscv32-unknown-elf/bin/pk",
             test_binary.string(),
-            boost::process::std_out > pipe_stream
+            boost::process::std_out > buffer,
+            boost::process::std_err > buffer,
+            io_service
         );
-        boost::process::child diff(
-                "/usr/bin/diff", "-Nur", "--color",
-                expectation_path.string(), "-",
-                boost::process::std_in < pipe_stream
-        );
-        vm.wait();
-        diff.wait();
+        io_service.run();
 
-        return diff.exit_code();
+        return test_result{ test_status::successful, spike.exit_code(), buffer.get() };
     }
 
     static test_results run_in_path(const std::filesystem::path test_directory)
@@ -117,26 +137,37 @@ namespace elna
             {
                 continue;
             }
-            int status{ 0 };
+            test_result result;
 
+            std::cout << "Running " << test_entry << std::endl;
             try
             {
-                status = build_test(test_entry);
+                result = build_test(test_entry);
+                if (result.status == test_status::successful)
+                {
+                    result = run_test(test_entry);
+                }
+                result = check_expectation(test_entry, result);
             }
             catch (const boost::process::process_error& exception)
             {
-                std::cout << exception.what() << std::endl;
-                status = 3;
-                continue;
+                result.status = test_status::build_failed;
+                result.output = exception.what();
+                std::cout << result.output << std::endl;
             }
-            if (status == 0)
-            {
-                status = run_test(test_entry);
-            }
-            results.add_exit_code(status);
+            print_result(test_entry, result);
+            results.add_exit_code(result.status);
         }
         return results;
     }
+
+    void print_result(const std::filesystem::directory_entry& test_entry, const test_result& result)
+    {
+        if (result.status != test_status::successful)
+        {
+            std::cout << test_entry << " failed." << std::endl;
+        }
+    }
 };
 
 int main()