diff --git a/TODO b/TODO
index b35e3f4..3c102fc 100644
--- a/TODO
+++ b/TODO
@@ -13,3 +13,5 @@
 - Error message with an empty file wrongly says that a ")" is expected.
 - Support any expressions for constants.
 - Name analysis should fail if there are undefined symbols.
+- type_mismatch error should get second type argument for the
+  expected type.
diff --git a/backend/target.cpp b/backend/target.cpp
index 5ab5d04..aa105c1 100644
--- a/backend/target.cpp
+++ b/backend/target.cpp
@@ -199,14 +199,11 @@ namespace elna::riscv
         ELFIO::relocation_section_accessor rela(writer, rel_sec);
         auto _writer = std::make_shared<elfio_writer>(text_sec, ro_sec, syma, stra);
 
-        // visitor _visitor{ _writer, table };
-        // _visitor.visit(ast);
         auto references = generate(intermediate_code_generator, table, _writer);
 
         syma.arrange_local_symbols();
 
         for (auto& reference : references)
-        // for (auto& reference : _visitor.references)
         {
             ELFIO::Elf_Word relocated_symbol = lookup(syma, reference.name);
 
diff --git a/include/elna/source/result.hpp b/include/elna/source/result.hpp
index acbc2cd..c219e50 100644
--- a/include/elna/source/result.hpp
+++ b/include/elna/source/result.hpp
@@ -134,7 +134,9 @@ namespace elna::source
         enum class operation
         {
             dereference,
-            argument
+            argument,
+            arithmetic,
+            comparison
         };
 
         /**
diff --git a/include/elna/source/semantic.hpp b/include/elna/source/semantic.hpp
index 94ea5dc..afde1da 100644
--- a/include/elna/source/semantic.hpp
+++ b/include/elna/source/semantic.hpp
@@ -82,6 +82,7 @@ namespace elna::source
         void visit(integer_literal *literal) override;
         void visit(boolean_literal *literal) override;
         void visit(unary_expression *expression) override;
+        void visit(binary_expression *expression) override;
         void visit(call_statement *statement) override;
         void visit(constant_definition *definition) override;
     };
diff --git a/include/elna/source/types.hpp b/include/elna/source/types.hpp
index 64bc3a3..917ddda 100644
--- a/include/elna/source/types.hpp
+++ b/include/elna/source/types.hpp
@@ -26,6 +26,9 @@ namespace elna::source
          * \return The type size in bytes.
          */
         virtual std::size_t size() const noexcept;
+
+        friend bool operator==(const type& lhs, const type& rhs) noexcept;
+        friend bool operator!=(const type& lhs, const type& rhs) noexcept;
     };
 
     /**
@@ -43,6 +46,9 @@ namespace elna::source
          * \param byte_size The type size in bytes.
          */
         primitive_type(const std::string& type_name, const std::size_t byte_size);
+
+        bool operator==(const primitive_type& that) const noexcept;
+        bool operator!=(const primitive_type& that) const noexcept;
     };
 
     /**
@@ -60,6 +66,9 @@ namespace elna::source
          * \param byte_size The type size in bytes.
          */
         pointer_type(std::shared_ptr<const type> base_type, const std::size_t byte_size);
+
+        bool operator==(const pointer_type& that) const noexcept;
+        bool operator!=(const pointer_type& that) const noexcept;
     };
 
     /**
@@ -77,8 +86,14 @@ namespace elna::source
          * \param byte_size Function pointer size.
          */
         procedure_type(std::vector<std::shared_ptr<const type>> arguments, const std::size_t byte_size);
+
+        bool operator==(const procedure_type& that) const noexcept;
+        bool operator!=(const procedure_type& that) const noexcept;
     };
 
+    bool operator==(const type& lhs, const type& rhs) noexcept;
+    bool operator!=(const type& lhs, const type& rhs) noexcept;
+
     inline const primitive_type boolean_type{ "Boolean", 1 };
     inline const primitive_type int_type{ "Int", 4 };
 }
diff --git a/package.json b/package.json
index 4bb492e..ce54348 100644
--- a/package.json
+++ b/package.json
@@ -5,7 +5,8 @@
   "main": "tools/index.js",
   "type": "module",
   "scripts": {
-    "cross": "node tools/cross.js"
+    "start": "node tools/cross.js",
+	"test": "node tools/tester.js"
   },
   "author": "Eugen Wissner <belka@caraus.de>",
   "license": "MPL-2.0",
diff --git a/source/lexer.cpp b/source/lexer.cpp
index cc414de..5a6ff71 100644
--- a/source/lexer.cpp
+++ b/source/lexer.cpp
@@ -216,6 +216,10 @@ namespace elna::source
                 return "«proc»";
             case type::comparison_operator:
                 return "«comparison_operator»";
+            case type::hat:
+                return "«^»";
+            case type::at:
+                return "«@»";
         };
         assert(false);
     }
diff --git a/source/semantic.cpp b/source/semantic.cpp
index ec1e383..45c04be 100644
--- a/source/semantic.cpp
+++ b/source/semantic.cpp
@@ -196,6 +196,56 @@ namespace elna::source
         }
     }
 
+    void type_analysis_visitor::visit(binary_expression *expression)
+    {
+        empty_visitor::visit(expression);
+
+        switch (expression->operation())
+        {
+            case binary_operator::sum:
+            case binary_operator::subtraction:
+            case binary_operator::multiplication:
+            case binary_operator::division:
+            case binary_operator::less:
+            case binary_operator::greater:
+            case binary_operator::less_equal:
+            case binary_operator::greater_equal:
+                if (expression->lhs().data_type != nullptr && expression->rhs().data_type != nullptr)
+                {
+                    auto lhs_type = std::dynamic_pointer_cast<const primitive_type>(expression->lhs().data_type);
+                    auto rhs_type = std::dynamic_pointer_cast<const primitive_type>(expression->rhs().data_type);
+
+                    std::unique_ptr<type_mismatch> new_error;
+                    if (lhs_type == nullptr || *lhs_type != int_type)
+                    {
+                        new_error = std::make_unique<type_mismatch>(lhs_type,
+                                type_mismatch::operation::arithmetic, this->filename, expression->lhs().position());
+                    }
+                    if (rhs_type == nullptr || *rhs_type != int_type)
+                    {
+                        new_error = std::make_unique<type_mismatch>(rhs_type,
+                                type_mismatch::operation::arithmetic, this->filename, expression->rhs().position());
+                    }
+                    if (new_error != nullptr)
+                    {
+                        m_errors.push_back(std::move(new_error));
+                    }
+                }
+            break;
+            case binary_operator::equals:
+            case binary_operator::not_equals:
+                if (expression->lhs().data_type != nullptr && expression->rhs().data_type != nullptr)
+                {
+                    if (expression->lhs().data_type != expression->rhs().data_type)
+                    {
+                        auto new_error = std::make_unique<type_mismatch>(expression->rhs().data_type,
+                                type_mismatch::operation::comparison, this->filename, expression->rhs().position());
+                    }
+                }
+            break;
+        }
+    }
+
     void type_analysis_visitor::visit(call_statement *statement)
     {
         auto call_info = std::dynamic_pointer_cast<intrinsic_info>(this->table->lookup(statement->name()));
diff --git a/source/types.cpp b/source/types.cpp
index 6e86771..dbc96a9 100644
--- a/source/types.cpp
+++ b/source/types.cpp
@@ -17,13 +17,80 @@ namespace elna::source
    {
    }
 
+    bool primitive_type::operator==(const primitive_type& that) const noexcept
+    {
+        return this->type_name == that.type_name;
+    }
+
+    bool primitive_type::operator!=(const primitive_type& that) const noexcept
+    {
+        return this->type_name != that.type_name;
+    }
+
     pointer_type::pointer_type(std::shared_ptr<const type> base_type, const std::size_t byte_size)
         : type(byte_size), base_type(base_type)
     {
     }
 
+    bool pointer_type::operator==(const pointer_type& that) const noexcept
+    {
+        return this->base_type == that.base_type;
+    }
+
+    bool pointer_type::operator!=(const pointer_type& that) const noexcept
+    {
+        return this->base_type != that.base_type;
+    }
+
     procedure_type::procedure_type(std::vector<std::shared_ptr<const type>> arguments, const std::size_t byte_size)
         : arguments(std::move(arguments)), type(byte_size)
     {
     }
+
+    bool procedure_type::operator==(const procedure_type &that) const noexcept
+    {
+        return this->arguments == that.arguments;
+    }
+
+    bool procedure_type::operator!=(const procedure_type &that) const noexcept
+    {
+        return this->arguments != that.arguments;
+    }
+
+    bool operator==(const type& lhs, const type& rhs) noexcept
+    {
+        {
+            auto lhs_type = dynamic_cast<const primitive_type *>(&lhs);
+            auto rhs_type = dynamic_cast<const primitive_type *>(&rhs);
+
+            if (lhs_type != nullptr && rhs_type != nullptr)
+            {
+                return *lhs_type == *rhs_type;
+            }
+        }
+        {
+            auto lhs_type = dynamic_cast<const pointer_type *>(&lhs);
+            auto rhs_type = dynamic_cast<const pointer_type *>(&rhs);
+
+            if (lhs_type != nullptr && rhs_type != nullptr)
+            {
+                return *lhs_type == *rhs_type;
+            }
+        }
+        {
+            auto lhs_type = dynamic_cast<const procedure_type *>(&lhs);
+            auto rhs_type = dynamic_cast<const procedure_type *>(&rhs);
+
+            if (lhs_type != nullptr && rhs_type != nullptr)
+            {
+                return *lhs_type == *rhs_type;
+            }
+        }
+        return false;
+    }
+
+    bool operator!=(const type& lhs, const type& rhs) noexcept
+    {
+        return !(lhs == rhs);
+    }
 }
diff --git a/tools/tester.js b/tools/tester.js
index 210f085..cb6b633 100644
--- a/tools/tester.js
+++ b/tools/tester.js
@@ -32,11 +32,13 @@ async function compileTest (parsedPath) {
   })
 }
 
-function checkFailure (parsedPath, buildResult) {
+async function checkFailure (parsedPath, buildResult) {
+  const failureFile = path.resolve('./tests/failures', `${parsedPath.name}.txt`)
+
+  await fs.access(failureFile)
   const diffArguments = [
     '-u', '--color=always',
-    path.resolve('./tests/failures', `${parsedPath.name}.txt`),
-    '-'
+    failureFile, '-'
   ]
 
   try {
@@ -97,16 +99,22 @@ async function runVM(cpioImage) {
 
 async function runInDirectory (directoryPath) {
   let failed = 0
+  const sources = await glob(path.join(directoryPath, '*.eln'))
 
-  for (const testEntry of await glob(path.join(directoryPath, '*.eln'))) {
+  for (const testEntry of sources) {
     const parsedPath = path.parse(testEntry)
 
     console.log(`Compiling ${parsedPath.base}.`)
     const buildResult = await compileTest(parsedPath)
 
     if (buildResult.code !== 0) {
-      if (!(await checkFailure(parsedPath, buildResult))) {
+      try {
+        if (!(await checkFailure(parsedPath, buildResult))) {
+          ++failed
+        }
+      } catch (e) {
         ++failed
+        console.log(buildResult.output)
       }
       continue
     }
@@ -119,7 +127,7 @@ async function runInDirectory (directoryPath) {
   await runVM(cpioImage)
 
   return {
-    total: (await glob(path.join(directoryPath, 'failures/*'))).length,
+    total: sources.length,
     failed,
 
     passed () {