diff --git a/include/builtin_functions.hpp b/include/builtin_functions.hpp
new file mode 100644
index 0000000..5fba95c
--- /dev/null
+++ b/include/builtin_functions.hpp
@@ -0,0 +1,23 @@
+#pragma once
+
+#include <string>
+#include <iostream>
+
+// for clangd
+
+namespace info::builtin {
+
+template<typename T>
+inline void Print(const T& value) { // only for strings ??
+  std::cout << "\x1b[1;32mOutput:\x1b[0m " << value << '\n';
+}
+
+template<typename T>
+inline T Read() {
+  T value;
+  std::cout << "\x1b[1;32mInput:\x1b[0m ";
+  std::cin >> value;
+  return value;
+}
+
+} // namespace info
diff --git a/include/builtin_methods.hpp b/include/builtin_methods.hpp
deleted file mode 100644
index 0d0cfa7..0000000
--- a/include/builtin_methods.hpp
+++ /dev/null
@@ -1,31 +0,0 @@
-#pragma once
-
-#include <vector>
-
-// for clangd
-#include "types.hpp"
-#include "utils.hpp"
-
-// TODO
-
-namespace info {
-
-struct BuiltinFunction {
-public:
-  BuiltinFunction(const std::vector<utils::IdType>& argument_types, utils::IdType return_type)
-      : argument_types(argument_types), return_type(return_type) {}
-
-  static std::optional<BuiltinFunction> FindMethod(const std::string& name, info::type::TypeManager& type_manager) {
-    return std::nullopt;
-  }
-
-  static std::optional<BuiltinFunction> FindStaticMethod(const std::string& name, info::type::TypeManager& type_manager) {
-    return std::nullopt;
-  }
-
-public:
-  std::vector<utils::IdType> argument_types;
-  utils::IdType return_type;
-};
-
-} // namespace info
diff --git a/include/contexts.hpp b/include/contexts.hpp
index 3993ea0..ae3825f 100644
--- a/include/contexts.hpp
+++ b/include/contexts.hpp
@@ -7,6 +7,7 @@
 #include <unordered_map>
 
 // for clangd
+#include "error_handling.hpp"
 #include "utils.hpp"
 
 namespace info {
@@ -15,7 +16,7 @@ template<typename Value, typename ValueManager>
 class ContextManager {
 public:
   ContextManager() {
-    contexts_.emplace_back();
+    contexts_.emplace_back(true); // no difference ??
   }
 
   template<typename T>
@@ -57,67 +58,103 @@ public:
     return &value_manager_;
   }
 
-  void EnterContext() {
-    contexts_.emplace_back();
+  void EnterContext(bool is_hiding_previous = false) {
+    contexts_.emplace_back(is_hiding_previous);
   }
 
   void ExitContext() {
     if (contexts_.empty()) {
-      // error
+      error_handling::HandleInternalError("contexts_ is empty",
+                                          "ContextManager.ExitContext",
+                                          std::nullopt);
     }
 
     contexts_.pop_back();
   }
 
-  void ExitFromAllContexts() {
-    contexts_.clear();
-    contexts_.emplace_back();
+  void ChangeHidingOfCurrentContextTo(bool is_hiding_previous) {
+    contexts_.back().ChangeHidingTo(is_hiding_previous);
   }
 
   bool DefineVariable(const std::string& name, utils::IdType value_id) {
-    // check in previous contexts ??
     return contexts_.back().DefineVariable(name, value_id);
   }
 
   bool DefineLocalType(const std::string& name, utils::IdType type_id) {
-    if (GetLocalType(name).has_value()) {
-      return false;
-    }
     return contexts_.back().DefineLocalType(name, type_id);
   }
 
+  bool AssignVariable(const std::string& name, utils::IdType value_id) {
+    for (ssize_t i = (ssize_t)contexts_.size() - 1; i >= 0; --i) {
+      if (contexts_[i].AssignVariable(name, value_id)) {
+        return true;
+      }
+
+      if (contexts_[i].IsHidingPrevious()) {
+        break;
+      }
+    }
+    return false;
+  }
+
+  bool AssignLocalType(const std::string& name, utils::IdType type_id) {
+    for (ssize_t i = (ssize_t)contexts_.size() - 1; i >= 0; --i) {
+      if (contexts_[i].AssignLocalType(name, type_id)) {
+        return true;
+      }
+
+      if (contexts_[i].IsHidingPrevious()) {
+        break;
+      }
+    }
+    return false;
+  }
+
   bool RemoveVariable(const std::string& name) {
     for (ssize_t i = (ssize_t)contexts_.size() - 1; i >= 0; --i) {
       if (contexts_[i].RemoveVariable(name)) {
         return true;
       }
+
+      if (contexts_[i].IsHidingPrevious()) {
+        break;
+      }
     }
     return false;
   }
 
-  void EnterVariableContext(const std::string& name, utils::IdType value_id) {
-    // for variable namespaces, for loops
-    contexts_.emplace_back();
+  void EnterVariableContext(const std::string& name,
+                            utils::IdType value_id,
+                            bool is_hiding_previous = false) {
+    EnterContext(is_hiding_previous);
 
     DefineVariable(name, value_id);
   }
 
-  std::optional<utils::IdType> GetVariableInfo(const std::string& name) {
+  std::optional<utils::IdType> FindVariable(const std::string& name) {
     for (ssize_t i = (ssize_t)contexts_.size() - 1; i >= 0; --i) {
-      auto maybe_type = contexts_[i].GetVariableInfo(name);
-      if (maybe_type.has_value()) {
-        return maybe_type.value();
+      auto maybe_variable = contexts_[i].FindVariable(name);
+      if (maybe_variable.has_value()) {
+        return maybe_variable.value();
+      }
+
+      if (contexts_[i].IsHidingPrevious()) {
+        break;
       }
     }
     return std::nullopt;
   }
 
-  std::optional<utils::IdType> GetLocalType(const std::string& name) {
+  std::optional<utils::IdType> FindLocalType(const std::string& name) {
     for (ssize_t i = (ssize_t)contexts_.size() - 1; i >= 0; --i) {
-      auto maybe_type = contexts_[i].GetLocalType(name);
+      auto maybe_type = contexts_[i].FindLocalType(name);
       if (maybe_type.has_value()) {
         return maybe_type.value();
       }
+
+      if (contexts_[i].IsHidingPrevious()) {
+        break;
+      }
     }
     return std::nullopt;
   }
@@ -125,10 +162,10 @@ public:
 private:
   class Context {
   public:
-    Context() = default;
+    explicit Context(bool is_hiding_previous) : is_hiding_previous_(is_hiding_previous) {}
 
     bool DefineVariable(const std::string& name, utils::IdType value_id) {
-      if (name == "_") { // placeholder // TODO: ??
+      if (name == "_") { // placeholder
         return true;
       }
 
@@ -147,11 +184,33 @@ private:
       return true;
     }
 
+    bool AssignVariable(const std::string& name, utils::IdType value_id) {
+      if (name == "_") { // placeholder
+        return true;
+      }
+
+      auto variable_iter = variables_.find(name);
+      if (variable_iter == variables_.end()) {
+        return false;
+      }
+      variable_iter->second = value_id;
+      return true;
+    }
+
+    bool AssignLocalType(const std::string& name, utils::IdType type_id) {
+      auto local_type_iter = local_types_.find(name);
+      if (local_type_iter == local_types_.end()) {
+        return false;
+      }
+      local_type_iter->second = type_id;
+      return true;
+    }
+
     bool RemoveVariable(const std::string& name) {
       return variables_.erase(name);
     }
 
-    std::optional<utils::IdType> GetVariableInfo(const std::string& name) {
+    std::optional<utils::IdType> FindVariable(const std::string& name) {
       auto variable_iter = variables_.find(name);
 
       if (variable_iter == variables_.end()) {
@@ -161,7 +220,7 @@ private:
       return variable_iter->second;
     }
 
-    std::optional<utils::IdType> GetLocalType(const std::string& name) {
+    std::optional<utils::IdType> FindLocalType(const std::string& name) {
       auto local_abstract_type_iter = local_types_.find(name);
 
       if (local_abstract_type_iter == local_types_.end()) {
@@ -171,9 +230,19 @@ private:
       return local_abstract_type_iter->second;
     }
 
+    bool IsHidingPrevious() {
+      return is_hiding_previous_;
+    }
+
+    void ChangeHidingTo(bool is_hiding_previous) {
+      is_hiding_previous_ = is_hiding_previous;
+    }
+
   private:
     std::unordered_map<std::string, utils::IdType> variables_;
     std::unordered_map<std::string, utils::IdType> local_types_;
+
+    bool is_hiding_previous_ = false;
   };
 
   std::vector<Context> contexts_;
diff --git a/include/error_handling.hpp b/include/error_handling.hpp
index 690cb72..619e51c 100644
--- a/include/error_handling.hpp
+++ b/include/error_handling.hpp
@@ -34,8 +34,15 @@ inline void HandleGeneralError(const std::string& message) {
   exit(1);
 }
 
-inline void HandleInternalError(const std::string& message, const std::string& place) {
-  std::cerr << "\x1b[1;31mInternal Error:\x1b[0m " << message << " at " << place << ".\n";
+inline void HandleInternalError(const std::string& message,
+                                const std::string& place,
+                                std::optional<const interpreter::tokens::BaseNode*> node) {
+  std::cerr << "\x1b[1;31mInternal Error:\x1b[0m " << message << " at " << place;
+  if (node.has_value()) {
+    std::cerr << ", at ";
+    PrintPosition(std::cerr, node.value()->start_position, node.value()->end_position);
+  }
+  std::cerr << ".\n";
   exit(1);
 }
 
diff --git a/include/execute_visitor.hpp b/include/execute_visitor.hpp
index 3e31aec..53dd7db 100644
--- a/include/execute_visitor.hpp
+++ b/include/execute_visitor.hpp
@@ -24,8 +24,10 @@ public:
       type_context_manager_(type_context_manager),
       context_manager_(context_manager) {}
 
-  void VisitSourceFile(SourceFile*) override {
-    error_handling::HandleInternalError("VisitSourceFile unavailible", "ExecuteVisitor.VisitSourceFile");
+  void VisitSourceFile(SourceFile* node) override {
+    error_handling::HandleInternalError("VisitSourceFile unavailible",
+                                        "ExecuteVisitor.VisitSourceFile",
+                                        &node->base);
   };
 
   void ExecutePartition(interpreter::tokens::PartitionStatement* partition) {
@@ -157,6 +159,13 @@ private:
     }
     return maybe_internal_value_info.value();
   }
+
+  //
+
+  bool HandleBuiltinFunctionCall(FunctionCallExpression* node);
+
+  bool HandleBuiltinTypeclassFunctionCall(FunctionCallExpression* node);
+
 private:
   info::GlobalInfo& global_info_;
   info::TypeclassGraph& typeclass_graph_;
diff --git a/include/interpreter_tree.hpp b/include/interpreter_tree.hpp
index 0c68668..2635490 100644
--- a/include/interpreter_tree.hpp
+++ b/include/interpreter_tree.hpp
@@ -523,6 +523,9 @@ struct FunctionCallExpression {
   // only one from two is present
   std::optional<utils::IdType> function_id_;
   std::optional<utils::IdType> graph_id_; // for type or typeclass
+
+  std::optional<std::string> abstract_type_name_; // for typeclasses
+
   bool is_method_of_first_argument_ = false;
 };
 
diff --git a/include/type_check_visitor.hpp b/include/type_check_visitor.hpp
index 213f105..c5bd669 100644
--- a/include/type_check_visitor.hpp
+++ b/include/type_check_visitor.hpp
@@ -162,6 +162,13 @@ private:
       FunctionCallExpression* node,
       info::definition::AnyType* defined_type,
       bool is_method);
+
+  //
+
+  bool HandleBuiltinFunctionCall(FunctionCallExpression* node);
+
+  bool HandleBuiltinTypeclassFunctionCall(FunctionCallExpression* node);
+
 private:
   info::GlobalInfo::NamespaceVisitor namespace_visitor_;
   info::GlobalInfo& global_info_;
diff --git a/include/types.hpp b/include/types.hpp
index 14d63ee..f6c99f6 100644
--- a/include/types.hpp
+++ b/include/types.hpp
@@ -44,6 +44,10 @@ public:
   std::optional<utils::IdType> GetFieldType(const std::string& name,
                                             const std::unordered_set<utils::IdType>& type_namespaces) const;
 
+  const std::string& GetName() {
+    return name_;
+  }
+
   bool HasTypeclass(utils::IdType graph_id) {
     return requirement_graph_ids_.count(graph_id) != 0;
   }
diff --git a/src/build_visitor.cpp b/src/build_visitor.cpp
index 49c0cd6..239ba67 100644
--- a/src/build_visitor.cpp
+++ b/src/build_visitor.cpp
@@ -62,7 +62,9 @@ void BuildVisitor::Visit(Namespace* node) {
     } else if (modifier == "var") {
       node->modifier = utils::ClassInternalsModifier::Var;
     } else {
-      error_handling::HandleInternalError("Can't parse namespace modifier", "BuildVisitor.Namespace");
+      error_handling::HandleInternalError("Can't parse namespace modifier",
+                                          "BuildVisitor.Namespace",
+                                          &node->base);
     }
   } else {
     node->modifier = utils::ClassInternalsModifier::Static;
diff --git a/src/execute_visitor.cpp b/src/execute_visitor.cpp
index 8b8363f..5498c20 100644
--- a/src/execute_visitor.cpp
+++ b/src/execute_visitor.cpp
@@ -1,9 +1,11 @@
-// for clangd
-#include "../include/execute_visitor.hpp"
-#include <cwchar>
 #include <optional>
 #include <variant>
 
+// for clangd
+#include "../include/execute_visitor.hpp"
+#include "../include/builtin_functions.hpp"
+
+
 // TODO
 
 namespace interpreter {
@@ -46,7 +48,9 @@ void ExecuteVisitor::Visit(FunctionDeclaration*) {} // no value
 
 void ExecuteVisitor::Visit(FunctionDefinitionStatement* node) { // visited on function call
   // Visit(node->definition.get());
+  context_manager_.EnterContext();
   Visitor::Visit(node->value);
+  context_manager_.ExitContext();
 }
 
 void ExecuteVisitor::Visit(TypeDefinitionStatement*) {} // no value
@@ -244,8 +248,12 @@ void ExecuteVisitor::Visit(ForLoop* node) {
   info::value::ArrayValue* interval = ExtractValue<info::value::ArrayValue>(current_value_, node->base);
 
   for (auto& value : interval->elements) {
+    context_manager_.EnterContext(); // TODO
+
     current_value_ = value;
-    Visitor::Visit(node->variable);
+    is_const_definition_ = node->variable_modifier;
+    Visitor::Visit(node->variable); // TODO: assign variable, instead of making new
+    is_const_definition_ = std::nullopt;
 
     Visitor::Visit(node->statement);
     if (active_loop_control_expression_.has_value()) {
@@ -258,6 +266,8 @@ void ExecuteVisitor::Visit(ForLoop* node) {
 
     }
     result.push_back(current_value_);
+
+    context_manager_.ExitContext(); // TODO
   }
 
   current_value_ = context_manager_.AddValue(
@@ -302,10 +312,11 @@ void ExecuteVisitor::Visit(Block* node) {
     Visitor::Visit(statement);
     if (returned_value_.has_value()) {
       current_value_ = returned_value_.value();
-      returned_value_ = std::nullopt; // ??
+      returned_value_ = std::nullopt; // TODO: ?? ("return" exits only from one block)
       return;
     }
   }
+
   context_manager_.ExitContext();
 
   current_value_ = context_manager_.AddValue(
@@ -326,36 +337,6 @@ void ExecuteVisitor::Visit(LoopControlExpression& node) {
 
 // Operators
 
-// TODO: function call expression used instead
-/////////////////////////////////////////////////
-// void ExecuteVisitor::Visit(BinaryOperatorExpression* node) {
-//   context_manager_.EnterContext();
-//
-//   auto maybe_function_definition = global_info_.GetFunctionInfo(node->function_id_).definition;
-//
-//   if (maybe_function_definition.has_value()) {
-//     Visitor::Visit(node->left_expression);
-//     // TODO: custom argument value types, references, etc.
-//     current_value_ = context_manager_.ToModifiedValue(current_value_, utils::ValueType::Const);
-//     context_manager_.DefineVariable(
-//       node->is_method_ ? utils::ClassInternalVarName : maybe_function_definition.value().argument_names[0],
-//       current_value_);
-//
-//     Visitor::Visit(node->left_expression);
-//     // TODO: custom argument value types, references, etc.
-//     current_value_ = context_manager_.ToModifiedValue(current_value_, utils::ValueType::Const);
-//     context_manager_.DefineVariable(maybe_function_definition.value().argument_names[node->is_method_ ? 0 : 1], current_value_);
-//
-//     Visit(maybe_function_definition.value().node);
-//   } else {
-//     // TODO: builtin operators, etc. (imports?)
-//     error_handling::HandleRuntimeError("Binary operator definition not found", node->base);
-//   }
-//
-//   context_manager_.ExitContext();
-// }
-/////////////////////////////////////////////////
-
 void ExecuteVisitor::Visit(ReferenceExpression* node) {
   // TODO: check, that there is no references to "Tmp"??
   Visit(node->expression.get());
@@ -385,18 +366,18 @@ void ExecuteVisitor::Visit(AccessExpression* node) {
 
 // Other Expressions
 
-// TODO
-// TODO: typeclass functions
-// TODO: builtin functions
-// TODO: binary operator expression
+// TODO: refactor, separate to several functions
+// TODO: more builtin functions, better handling (??)
 void ExecuteVisitor::Visit(FunctionCallExpression* node) {
   context_manager_.EnterContext();
 
   if (node->prefix.has_value()) {
     if (std::holds_alternative<std::unique_ptr<SubExpressionToken>>(node->prefix.value())) {
       Visitor::Visit(*std::get<std::unique_ptr<SubExpressionToken>>(node->prefix.value()));
-      // modify value on const methods, etc. ??
-      context_manager_.DefineVariable(utils::ClassInternalVarName, current_value_);
+
+      if (!context_manager_.DefineVariable(utils::ClassInternalVarName, current_value_)) {
+        error_handling::HandleRuntimeError("Variable redefinition (mathod caller var)", node->base);
+      }
     } else if (std::holds_alternative<std::unique_ptr<TypeExpression>>(node->prefix.value())) {
       TypeExpression& prefix = *std::get<std::unique_ptr<TypeExpression>>(node->prefix.value());
 
@@ -407,46 +388,135 @@ void ExecuteVisitor::Visit(FunctionCallExpression* node) {
 
       CollectTypeContext(prefix.type);
     } else {
-      // error
+      error_handling::HandleInternalError("Unexpected prefix type",
+                                          "ExecuteVisitor.FunctionCallExpression",
+                                          &node->base);
     }
   } else {
     if (node->is_method_of_first_argument_) {
       Visitor::Visit(node->arguments[0]);
-      context_manager_.DefineVariable(utils::ClassInternalVarName, current_value_);
+      if (!context_manager_.DefineVariable(utils::ClassInternalVarName, current_value_)) {
+        error_handling::HandleRuntimeError("Variable redefinition (mathod caller var)", node->base);
+      }
     }
-    // TODO
   }
 
-  if (!node->function_id_.has_value()) {
-    // TODO: typeclass function
-    error_handling::HandleInternalError("Typeclass functions not implemented yet",
-                                        "ExecuteVisitor.FunctionCallExpression");
-  }
+  FunctionDeclaration* function_declaration = nullptr;
+  FunctionDefinitionStatement* function_definition = nullptr;
 
-  auto function_declaration = global_info_.GetFunctionInfo(node->function_id_.value()).declaration.value(); // checked in type_check_visitor
+  if (node->function_id_.has_value()) {
+    auto maybe_function_declaration_info = global_info_.GetFunctionInfo(node->function_id_.value()).declaration;
+
+    if (!maybe_function_declaration_info.has_value()) {
+      error_handling::HandleRuntimeError("Function declaration not found (for namespace function)", node->base);
+      // always namespace function ??
+    }
+
+    function_declaration = maybe_function_declaration_info.value().node;
+
+    auto maybe_function_definition_info = global_info_.GetFunctionInfo(node->function_id_.value()).definition;
+
+    if (!maybe_function_definition_info.has_value()) {
+      if (HandleBuiltinFunctionCall(node)) {
+        return;
+      }
+
+      error_handling::HandleRuntimeError("Function definition not found (by graph_id_)", node->base);
+    }
+
+    function_definition = maybe_function_definition_info.value().node;
+
+  } else if (node->graph_id_.has_value()) {
+    std::optional<FunctionDefinitionStatement*> maybe_function_definition;
+
+    auto maybe_function_graph_info = typeclass_graph_.GetFunctionInfo(node->name,
+                                                                      node->graph_id_.value());
+
+    if (!maybe_function_graph_info.has_value()) {
+      error_handling::HandleRuntimeError("Function info not found (by graph_id_)", node->base);
+    }
+
+    function_declaration = maybe_function_graph_info.value()->declaration;
+    maybe_function_definition = maybe_function_graph_info.value()->definition;
+
+    if (!maybe_function_definition.has_value()) {
+      if (typeclass_graph_.GetVertex(node->graph_id_.value()).modifier == info::TypeclassGraph::Modifier::Type) {
+        error_handling::HandleRuntimeError("Type function definition not found (by graph_id_)", node->base);
+      }
+
+      if (!node->abstract_type_name_.has_value()) {
+        error_handling::HandleInternalError("Typeclass function's abstract_type_name_ has no value",
+                                            "ExecuteVisitor.FunctionCallExpression",
+                                            &node->base);
+      }
+
+      auto maybe_type_id = context_manager_.FindLocalType(node->abstract_type_name_.value());
+      if (!maybe_type_id.has_value()) {
+        error_handling::HandleRuntimeError("Function's abstract type not found (by abstract_type_name_)", node->base);
+      }
+
+      auto maybe_type_info = global_info_.GetTypeInfo<info::definition::AnyType>(maybe_type_id.value());
+
+      if (!maybe_type_info.has_value()) {
+        error_handling::HandleRuntimeError("Function's abstract type replacement defined type is not AnyType", node->base);
+      }
+
+      maybe_function_graph_info = typeclass_graph_.GetFunctionInfo(node->name, maybe_type_info.value()->type.node->graph_id_);
+
+      if (!maybe_function_graph_info.has_value()) {
+      error_handling::HandleRuntimeError("Function info not found (by abstract type graph_id_)", node->base);
+    }
+
+      maybe_function_definition = maybe_function_graph_info.value()->definition;
+    }
+
+    if (!maybe_function_definition.has_value()) {
+      if (HandleBuiltinTypeclassFunctionCall(node)) {
+        return;
+      }
+
+      error_handling::HandleRuntimeError("Function definition not found (by graph_id_)", node->base);
+    }
+
+    function_definition = maybe_function_definition.value();
+  }
 
   for (size_t i = 0; i < node->parameters.size(); ++i) {
-    // TODO: local abstract types, absract types, etc.
+    utils::IdType type_id = 0;
 
-    context_manager_.DefineLocalType(function_declaration.parameters[i].type, node->parameters[i]->type_id_.value()); // TODO: check
-  }
+    if (node->parameters[i]->type_id_.has_value()) {
+      type_id = node->parameters[i]->type_id_.value();
+    } else {
+      auto maybe_parameter_type_id = context_manager_.FindLocalType(node->parameters[i]->type.type);
 
-  auto maybe_function_definition = global_info_.GetFunctionInfo(node->function_id_.value()).definition;
+      if (!maybe_parameter_type_id.has_value()) {
+        error_handling::HandleInternalError("Parameter type not found",
+                                           "ExecuteVisitor.FunctionCallExpression",
+                                            &node->base);
+      }
 
-  if (maybe_function_definition.has_value()) {
-    for (size_t i = (node->is_method_of_first_argument_ ? 1 : 0); i < node->arguments.size(); ++i) {
-      Visitor::Visit(node->arguments[i]);
-      // TODO: custom argument value types, references, etc.
-      current_value_ = context_manager_.ToModifiedValue(current_value_, utils::ValueType::Const);
-      context_manager_.DefineVariable(maybe_function_definition.value().argument_names[i], current_value_);
+      type_id = maybe_parameter_type_id.value();
     }
 
-    Visit(maybe_function_definition.value().node);
-  } else {
-    error_handling::HandleRuntimeError("Function definition not found", node->base);
-    // TODO: functions, defined in typeclasses ??
+    if (!context_manager_.DefineLocalType(function_declaration->parameters[i]->type,
+                                            type_id)) {
+      error_handling::HandleRuntimeError("Type redefinition (function argument)", node->base);
+    }
   }
 
+  for (size_t i = (node->is_method_of_first_argument_ ? 1 : 0); i < node->arguments.size(); ++i) {
+    Visitor::Visit(node->arguments[i]);
+
+    current_value_ = context_manager_.ToModifiedValue(current_value_, utils::ValueType::Const);
+    if (!context_manager_.DefineVariable(function_definition->definition->arguments[i],
+                                         current_value_)) {
+      error_handling::HandleRuntimeError("Variable redefinition (function argument)", node->base);
+    }
+  }
+
+  context_manager_.ChangeHidingOfCurrentContextTo(true);
+  Visit(function_definition);
+
   context_manager_.ExitContext();
 }
 
@@ -534,9 +604,10 @@ void ExecuteVisitor::Visit(TypeConstructor* node) {
 }
 
 // TODO
-void ExecuteVisitor::Visit(LambdaFunction*) {
+void ExecuteVisitor::Visit(LambdaFunction* node) {
   error_handling::HandleInternalError("Lambda function are not implemented yet",
-                                      "ExecuteVisitor.LambdaFunction");
+                                      "ExecuteVisitor.LambdaFunction",
+                                      &node->base);
 }
 
 void ExecuteVisitor::Visit(ArrayExpression* node) {
@@ -557,11 +628,13 @@ void ExecuteVisitor::Visit(ArrayExpression* node) {
 
 void ExecuteVisitor::Visit(NameExpression* node) { // TODO: check
   if (node->names.empty()) {
-    error_handling::HandleInternalError("Names array is empty", "ExecuteVisitor.NameExpression");
+    error_handling::HandleInternalError("Names array is empty",
+                                        "ExecuteVisitor.NameExpression",
+                                        &node->base);
   }
 
   std::optional<utils::IdType> maybe_variable_value =
-    context_manager_.GetVariableInfo(node->names[0]);
+    context_manager_.FindVariable(node->names[0]);
 
   if (!maybe_variable_value.has_value()) {
     error_handling::HandleRuntimeError("Variable not found", node->base);
@@ -599,7 +672,9 @@ void ExecuteVisitor::Visit(TupleName* node) { // TODO: check
   }
 
   if (!is_const_definition_.has_value()) {
-    error_handling::HandleInternalError("No value in is_const_definition_", "TypeCheckVisitor.TupleName");
+    error_handling::HandleInternalError("No value in is_const_definition_",
+                                        "TypeCheckVisitor.TupleName",
+                                        &node->base);
   }
 
   utils::ValueType value_type = context_manager_.GetValueType(value);
@@ -667,7 +742,8 @@ void ExecuteVisitor::Visit(AnnotatedName* node) { // TODO: check
 
   if (!is_const_definition_.has_value()) {
     error_handling::HandleInternalError("No value in is_const_definition_",
-                                        "TypeCheckVisitor.AnnotatedName");
+                                        "TypeCheckVisitor.AnnotatedName",
+                                        &node->base);
   }
 
   utils::ValueType value_type = context_manager_.GetValueType(current_value_);
@@ -749,16 +825,26 @@ bool ExecuteVisitor::HandleCondition(Expression& node, const BaseNode& base_node
   return *ExtractInternalValue<bool>(current_value_, base_node);
 }
 
-// TODO: handle abstract types, handle local abstract types, etc.
+// TODO: handle abstract types, handle local abstract types, etc. // partially done (check needed)
 void ExecuteVisitor::CollectTypeContext(const ParametrizedType& type) {
+  utils::IdType type_id = 0;
+
   if (!type.type_id_.has_value()) {
-    return;
+    auto maybe_local_type_id = context_manager_.FindLocalType(type.type);
+    if (!maybe_local_type_id.has_value()) {
+      return;
+    }
+    type_id = maybe_local_type_id.value(); // TODO: check
+  } else {
+    type_id = type.type_id_.has_value();
   }
 
-  auto maybe_type_info = global_info_.GetTypeInfo<info::definition::AnyType>(type.type_id_.value());
+  auto maybe_type_info = global_info_.GetTypeInfo<info::definition::AnyType>(type_id);
 
   if (!maybe_type_info.has_value()) {
-    error_handling::HandleInternalError("CollectTypeContext unimplemented anything except AnyType", "ExecuteVisitor.CollectTYpeContext");
+    error_handling::HandleInternalError("CollectTypeContext implemented only for AnyType",
+                                        "ExecuteVisitor.CollectTYpeContext",
+                                        std::nullopt);
   }
 
   info::definition::AnyType& type_info = *maybe_type_info.value(); // check, that has value ??
@@ -771,7 +857,6 @@ void ExecuteVisitor::CollectTypeContext(const ParametrizedType& type) {
   }
 }
 
-// TODO
 void ExecuteVisitor::CheckPattern(Pattern& node, const BaseNode& base_node) {
   utils::IdType value = current_value_;
 
@@ -798,5 +883,34 @@ void ExecuteVisitor::CheckPattern(Pattern& node, const BaseNode& base_node) {
   }
 }
 
+//
+
+bool ExecuteVisitor::HandleBuiltinFunctionCall(FunctionCallExpression* node) {
+  if (node->name == "print") {
+    if (node->arguments.size() < 1) {
+      error_handling::HandleInternalError("Builtin function \"print\" has 0 arguments",
+                                          "ExecuteVisitor.HandleBuiltinFunctionCall",
+                                          &node->base);
+    }
+
+    Visitor::Visit(node->arguments[0]);
+    info::builtin::Print(*ExtractInternalValue<std::string>(current_value_, node->base));
+
+    current_value_ = context_manager_.AddValue(info::value::InternalValue(info::value::Unit()),
+                                               utils::ValueType::Tmp);
+    return true;
+  } else if (node->name == "read") {
+    current_value_ = context_manager_.AddValue(info::value::InternalValue(info::builtin::Read<std::string>()),
+                                               utils::ValueType::Tmp);
+    return true;
+  }
+
+  return false;
+}
+
+bool ExecuteVisitor::HandleBuiltinTypeclassFunctionCall(FunctionCallExpression*) {
+  return false;
+}
+
 } // namespace interpreter
 
diff --git a/src/find_symbols_visitor.cpp b/src/find_symbols_visitor.cpp
index 654590d..80d56c2 100644
--- a/src/find_symbols_visitor.cpp
+++ b/src/find_symbols_visitor.cpp
@@ -195,7 +195,8 @@ void FindSymbolsVisitor::Visit(AnyAnnotatedType* node) {
 
   if (!maybe_typeclass_graph_id.has_value()) {
     error_handling::HandleInternalError("Can't add annotated type to typeclass graph",
-                                        "FindSymbolsVisitor.AnyAnnotatedType");
+                                        "FindSymbolsVisitor.AnyAnnotatedType",
+                                        &node->base);
   }
 
   node->graph_id_ = maybe_typeclass_graph_id.value();
diff --git a/src/global_info.cpp b/src/global_info.cpp
index bd35db5..1206937 100644
--- a/src/global_info.cpp
+++ b/src/global_info.cpp
@@ -69,13 +69,15 @@ void GlobalInfo::NamespaceVisitor::EnterNamespace(const std::string& name,
   }
 
   error_handling::HandleInternalError("Can't find namespace " + name,
-                                      "GlobalInfo.NamespaceVisitor.EnterNamespace");
+                                      "GlobalInfo.NamespaceVisitor.EnterNamespace",
+                                      std::nullopt);
 }
 
 void GlobalInfo::NamespaceVisitor::ExitNamespace() {
   if (namespace_stack_.size() <= 1) {
     error_handling::HandleInternalError("Can't exit from global namespace",
-                                        "GlobalInfo.NamespaceVisitor.ExitNamespace");
+                                        "GlobalInfo.NamespaceVisitor.ExitNamespace",
+                                        std::nullopt);
     return;
   }
 
@@ -169,7 +171,8 @@ utils::IdType GlobalInfo::NamespaceVisitor::AddType(const std::string& type,
 
   if (!std::holds_alternative<definition::AnyType>(moved_type_info.type)) {
     error_handling::HandleInternalError("Not AnyType constructor search is not implemented yet",
-                                        "GlobalInfo.NamespaceVisitor.AddType");
+                                        "GlobalInfo.NamespaceVisitor.AddType",
+                                        &base_node);
   }
 
   definition::AnyType& any_type_info = std::get<definition::AnyType>(moved_type_info.type);
@@ -198,7 +201,8 @@ utils::IdType GlobalInfo::NamespaceVisitor::AddType(const std::string& type,
         }
       } else {
         error_handling::HandleInternalError("Unexprected VariantType constructor node type",
-                                            "GlobalInfo.NamespaceVisitor.AddType");
+                                            "GlobalInfo.NamespaceVisitor.AddType",
+                                            &base_node);
       }
 
       constructor_info.name = constructor_name;
@@ -216,7 +220,8 @@ utils::IdType GlobalInfo::NamespaceVisitor::AddType(const std::string& type,
   } else {
     // TODO: constructors for function types (??), array types (??), ...
     error_handling::HandleInternalError("Not VariantType constructor search is not implemented yet",
-                                        "GlobalInfo.NamespaceVisitor.AddType");
+                                        "GlobalInfo.NamespaceVisitor.AddType",
+                                        &base_node);
   }
 
   return id;
@@ -466,7 +471,8 @@ std::optional<definition::Namespace*> GlobalInfo::GetTypeNamespace(utils::IdType
 
   if (!maybe_type_info.has_value()) {
     error_handling::HandleInternalError("Only AnyType is supported now",
-                                        "GlobalInfo.GetTypeNamespace");
+                                        "GlobalInfo.GetTypeNamespace",
+                                        std::nullopt);
   }
 
   std::string& name = maybe_type_info.value()->type.type;
@@ -511,7 +517,8 @@ std::optional<utils::IdType> GlobalInfo::AddTypeclassToGraph(utils::IdType typec
     std::string dependency = dependency_node->typeclass;
     if (dependency_node->parameters.size() > 0) {
       error_handling::HandleInternalError("Paramtrized typeclass requirements are not implemented yet",
-                                          "GlobalInfo.AddTypeclassToGraph");
+                                          "GlobalInfo.AddTypeclassToGraph",
+                                          std::nullopt);
     }
     dependencies.push_back(dependency);
   }
@@ -557,7 +564,8 @@ std::optional<utils::IdType> GlobalInfo::AddAnnotatedTypeToGraph(interpreter::to
     std::string dependency = dependency_node->typeclass;
     if (dependency_node->parameters.size() > 0) {
       error_handling::HandleInternalError("Paramtrized typeclass requirements are not implemented yet",
-                                          "GlobalInfo.AddAnnotatedTypeToGraph");
+                                          "GlobalInfo.AddAnnotatedTypeToGraph",
+                                          &node->base);
     }
     dependencies.push_back(dependency);
   }
diff --git a/src/link_symbols_visitor.cpp b/src/link_symbols_visitor.cpp
index 720a797..37454fc 100644
--- a/src/link_symbols_visitor.cpp
+++ b/src/link_symbols_visitor.cpp
@@ -172,7 +172,8 @@ void LinkSymbolsVisitor::AddTypeFunctionsToTypeclassGraph(utils::IdType type_id,
   auto maybe_type_graph_info = typeclass_graph_.GetTypeVertex(graph_id);
   if (!maybe_type_graph_info.has_value()) {
     error_handling::HandleInternalError("Type in typeclass graph is not marked as type",
-                                        "LinkSymbolsVisitor.AddTypeFunctionsToTypeclassGraph");
+                                        "LinkSymbolsVisitor.AddTypeFunctionsToTypeclassGraph",
+                                        &base_node);
   }
   auto type_graph_info = maybe_type_graph_info.value();
 
@@ -207,7 +208,8 @@ void LinkSymbolsVisitor::AddTypeFunctionsToTypeclassGraph(utils::IdType type_id,
         }
 
         error_handling::HandleInternalError("This code should be unreachable",
-                                            "LinkSymbolsVisitor.AddTypeFunctionsToTypeclassGraph");
+                                            "LinkSymbolsVisitor.AddTypeFunctionsToTypeclassGraph",
+                                            &base_node);
       }
     }
   }
diff --git a/src/main.cpp b/src/main.cpp
index f8eea47..9d73e0c 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -48,16 +48,16 @@ int main(int argc, char** argv) { // TODO, only test version
   info::ContextManager<info::value::Value, info::value::ValueManager> context_manager;
 
   interpreter::BuildVisitor build_visitor(parse_tree);
-  interpreter::PrintVisitor print_visitor(std::cout);
+  // interpreter::PrintVisitor print_visitor(std::cout);
   interpreter::FindSymbolsVisitor find_symbols_visitor(global_info);
   interpreter::LinkSymbolsVisitor link_symbols_visitor(global_info);
   interpreter::TypeCheckVisitor type_check_visitor(global_info, type_context_manager);
-  interpreter::TypedPrintVisitor typed_print_visitor(std::cout, type_context_manager);
+  // interpreter::TypedPrintVisitor typed_print_visitor(std::cout, type_context_manager);
 
   build_visitor.VisitSourceFile(source_file.get());
 
-  std::cout << "\n---------------------------------- Untyped -------------------------------------\n\n";
-  print_visitor.VisitSourceFile(source_file.get());
+  // std::cout << "\n---------------------------------- Untyped -------------------------------------\n\n";
+  // print_visitor.VisitSourceFile(source_file.get());
 
   find_symbols_visitor.VisitSourceFile(source_file.get());
   link_symbols_visitor.VisitSourceFile(source_file.get());
@@ -73,11 +73,11 @@ int main(int argc, char** argv) { // TODO, only test version
     global_info.GetPartitionInfo(maybe_main_partition_id.value());
 
   interpreter::ExecuteVisitor execute_visitor(global_info,
-                                              type_context_manager,
-                                              context_manager);
+                                             type_context_manager,
+                                             context_manager);
 
   execute_visitor.ExecutePartition(main_partition.node);
 
-  std::cout << "\n---------------------------------- Typed -------------------------------------\n\n";
-  typed_print_visitor.VisitSourceFile(source_file.get());
+  // std::cout << "\n---------------------------------- Typed -------------------------------------\n\n";
+  // typed_print_visitor.VisitSourceFile(source_file.get());
 }
diff --git a/src/type_check_visitor.cpp b/src/type_check_visitor.cpp
index 98100db..6a7f90d 100644
--- a/src/type_check_visitor.cpp
+++ b/src/type_check_visitor.cpp
@@ -112,9 +112,10 @@ void TypeCheckVisitor::Visit(Namespace* node) {
 void TypeCheckVisitor::Visit(ImportStatement*) {}
 
 // TODO
-void TypeCheckVisitor::Visit(AliasDefinitionStatement*) {
+void TypeCheckVisitor::Visit(AliasDefinitionStatement* node) {
   error_handling::HandleInternalError("Unimplemented",
-                                      "TypeCheckVisitor.AliasDefinitionStatement");
+                                      "TypeCheckVisitor.AliasDefinitionStatement",
+                                      &node->base);
 }
 
 void TypeCheckVisitor::Visit(VariableDefinitionStatement* node) {
@@ -194,7 +195,8 @@ void TypeCheckVisitor::Visit(FunctionDefinitionStatement* node) {
 
     if (maybe_curent_type.has_value() && maybe_current_typeclass.has_value()) {
       error_handling::HandleInternalError("Current namespace is belong to type and typeclass in same time",
-                                          "TypeCheckVisitor.FunctionDefinitionStatement");
+                                          "TypeCheckVisitor.FunctionDefinitionStatement",
+                                          &node->base);
     }
 
     if (!maybe_curent_type.has_value() && !maybe_current_typeclass.has_value()) {
@@ -219,7 +221,8 @@ void TypeCheckVisitor::Visit(FunctionDefinitionStatement* node) {
     auto maybe_function_info = typeclass_graph_.GetFunctionInfo(function_name, std::nullopt);
     if (!maybe_function_info.has_value()) {
       error_handling::HandleInternalError("FunctionInfo not found",
-                                          "TypeCheckVisitor.FunctionDefinitionStatement");
+                                          "TypeCheckVisitor.FunctionDefinitionStatement",
+                                          &node->base);
     }
 
     declaration = maybe_function_info.value()->declaration; // TODO: save declaration to global info ??
@@ -367,7 +370,8 @@ void TypeCheckVisitor::Visit(TypeConstructorPattern* node) { // TODO: match name
 
   if (!node->constructor->type_id_.has_value()) {
     error_handling::HandleInternalError("Type constructor pattern without type",
-                                        "TypeCheckVisitor.TypeConstructorPattern");
+                                        "TypeCheckVisitor.TypeConstructorPattern",
+                                        &node->base);
   }
 
   utils::IdType constructor_id = node->constructor->constructor_id_.value();
@@ -384,7 +388,8 @@ void TypeCheckVisitor::Visit(TypeConstructorPattern* node) { // TODO: match name
 
   if (!maybe_type_info.has_value()) {
     error_handling::HandleInternalError("Implemented only for AnyType",
-                                        "TypeCheckVisitor.TypeConstructorPattern");
+                                        "TypeCheckVisitor.TypeConstructorPattern",
+                                        &node->base);
   }
 
   info::definition::AnyType& type_info = *maybe_type_info.value();
@@ -712,17 +717,20 @@ void TypeCheckVisitor::Visit(AccessExpression* node) {
 
 // Other Expressions
 
-// TODO: builtin functions / methods
-// TODO: find & check definitions
+// TODO: more builtin functions, better handling (??)
 void TypeCheckVisitor::Visit(FunctionCallExpression* node) {
   std::optional<FunctionDeclaration*> maybe_function_declaration;
 
   std::unordered_map<std::string, utils::IdType> context;
 
-  // guaranteed, that name.size() > 0
+  if (node->name.empty()) {
+    error_handling::HandleInternalError("Empty name",
+                                        "TypeCheckVisitor.FunctionCallExpression",
+                                        &node->base);
+  }
+
   if (node->name[0] == '_') {
-    error_handling::HandleInternalError("Builtin functions/methods weren't implemented yet",
-                                        "TypeCheckVisitor.FunctionCallExpresssion");
+    error_handling::HandleTypecheckError("Only builtin functions can start with _. This function not found", node->base);
   }
 
   // try to find function declaration
@@ -737,7 +745,8 @@ void TypeCheckVisitor::Visit(FunctionCallExpression* node) {
         context);
     } else {
       error_handling::HandleInternalError("Unexpected prefix type",
-                                          "TypeCheckVisitor.FunctionCallExpression");
+                                          "TypeCheckVisitor.FunctionCallExpression",
+                                          &node->base);
     }
   } else {
     maybe_function_declaration = FindFunctionAndUpdate(node);
@@ -760,7 +769,8 @@ void TypeCheckVisitor::Visit(FunctionCallExpression* node) {
 
     if (context.count(parameter_name) != 0) {
       error_handling::HandleInternalError("Local abstract types with same name in one context",
-                                          "TypeCheckVisitor.FunctionCallExpresssion");
+                                          "TypeCheckVisitor.FunctionCallExpresssion",
+                                          &node->base);
     }
     context[parameter_name] = current_type_;
   }
@@ -779,7 +789,11 @@ void TypeCheckVisitor::Visit(FunctionCallExpression* node) {
 
   if (node->function_id_.has_value()) {
     if (!global_info_.GetFunctionInfo(node->function_id_.value()).definition.has_value()) {
-      error_handling::HandleTypecheckError("No function definition found (non-type function)", node->base);
+      if (HandleBuiltinFunctionCall(node)) {
+        return; // current_type_ - from HandleBuiltinFunctionCall
+      }
+
+      error_handling::HandleTypecheckError("No function definition found (namespace function)", node->base);
     }
   } else if (node->graph_id_.has_value()) {
     if (typeclass_graph_.GetVertex(node->graph_id_.value()).modifier != info::TypeclassGraph::Modifier::Typeclass) {
@@ -787,16 +801,22 @@ void TypeCheckVisitor::Visit(FunctionCallExpression* node) {
 
       if (!maybe_graph_function_info.has_value()) {
         error_handling::HandleInternalError("FunctionInfo by graph_id_ not found",
-                                            "TypeCheckVisitor.FunctionCallExpression");
+                                            "TypeCheckVisitor.FunctionCallExpression",
+                                            &node->base);
       }
 
       if (!maybe_graph_function_info.value()->definition.has_value()) {
+        if (HandleBuiltinTypeclassFunctionCall(node)) {
+          return; // current_type_ - from HandleBuiltinTypeclassFunctionCall
+        }
+
         error_handling::HandleTypecheckError("No function definition found (type function)", node->base);
       }
     }
   } else {
     error_handling::HandleInternalError("No function_id_ and graph_id_ found",
-                                        "TypeCheckVisitor.FunctionCallExpression");
+                                        "TypeCheckVisitor.FunctionCallExpression",
+                                        &node->base);
   }
 
   Visitor::Visit(function_declaration->type->types.back());
@@ -846,6 +866,8 @@ void TypeCheckVisitor::Visit(ReturnExpression* node) {
   Visitor::Visit(node->expression);
   returned_type_ = current_type_;
 
+  current_type_ = context_manager_.AddValue(info::type::InternalType::Unit, utils::ValueType::Tmp);
+
   node->base.type_ = current_type_;
 }
 
@@ -858,7 +880,9 @@ void TypeCheckVisitor::Visit(TypeConstructor* node) {
   }
 
   if (!node->constructor->type_id_.has_value()) {
-    error_handling::HandleInternalError("Type constructor without type", "TypeCheckVisitor.TypeConstructor");
+    error_handling::HandleInternalError("Type constructor without type",
+                                        "TypeCheckVisitor.TypeConstructor",
+                                        &node->base);
   }
 
   utils::IdType constructor_id = node->constructor->constructor_id_.value();
@@ -876,7 +900,8 @@ void TypeCheckVisitor::Visit(TypeConstructor* node) {
 
   if (!maybe_type_info.has_value()) { // TODO
     error_handling::HandleInternalError("Implemented only for AnyType",
-                                        "TypeCheckVisitor.TypeConstructor");
+                                        "TypeCheckVisitor.TypeConstructor",
+                                        &node->base);
   }
 
   info::definition::AnyType& type_info = *maybe_type_info.value();
@@ -925,7 +950,9 @@ void TypeCheckVisitor::Visit(TypeConstructor* node) {
 
   if (maybe_variant_type.has_value()) {
     if (!constructor_info.order.has_value()) {
-      error_handling::HandleInternalError("No order found in constructor of VariantType", "TypeCheckVisitor.TypeConstructor");
+      error_handling::HandleInternalError("No order found in constructor of VariantType",
+                                          "TypeCheckVisitor.TypeConstructor",
+                                          &node->base);
     }
     maybe_variant_type.value()->SetCurrentConstructor(constructor_info.order.value());
   }
@@ -944,7 +971,8 @@ void TypeCheckVisitor::Visit(TypeConstructor* node) {
 // TODO
 void TypeCheckVisitor::Visit(LambdaFunction* node) {
   error_handling::HandleInternalError("Unimplemented (unsolved type deduction problems)",
-                                      "TypeCheckVisitor.LambdaFunction");
+                                      "TypeCheckVisitor.LambdaFunction",
+                                      &node->base);
 
   node->base.type_ = current_type_;
 }
@@ -964,7 +992,9 @@ void TypeCheckVisitor::Visit(ArrayExpression* node) {
   }
 
   if (node->elements.empty()) {
-    error_handling::HandleInternalError("Element size is 0", "TypeCheckVisitor.ArrayExpression");
+    error_handling::HandleInternalError("Element size is 0",
+                                        "TypeCheckVisitor.ArrayExpression",
+                                        &node->base);
   }
 
   current_type_ = context_manager_.AddValue(
@@ -981,10 +1011,12 @@ void TypeCheckVisitor::Visit(PartitionName*) {} // Handled in partition ( execut
 void TypeCheckVisitor::Visit(NameExpression* node) {
   // TODO: move, etc.
   if (node->names.empty()) {
-    error_handling::HandleInternalError("Name expression with zero names", "TypeCheckVisitor.NameExpression");
+    error_handling::HandleInternalError("Name expression with zero names",
+                                        "TypeCheckVisitor.NameExpression",
+                                        &node->base);
   }
 
-  auto maybe_variable_type = context_manager_.GetVariableInfo(node->names[0]);
+  auto maybe_variable_type = context_manager_.FindVariable(node->names[0]);
 
   if (!maybe_variable_type.has_value()) {
     error_handling::HandleTypecheckError("Variable not found", node->base);
@@ -1019,18 +1051,20 @@ void TypeCheckVisitor::Visit(TupleName* node) {
     type = maybe_defined_type_value.value()->GetType();
   }
 
-  std::optional<info::type::TupleType*> maybe_type_value = context_manager_.GetValue<info::type::TupleType>(type);
-
-  if (maybe_type_value.has_value()) {
+  auto maybe_type_value = context_manager_.GetValue<info::type::TupleType>(type);
+  if (!maybe_type_value.has_value()) {
     error_handling::HandleTypecheckError("Mismatched types in tuple variable definition", node->base);
   }
+  info::type::TupleType* type_value = maybe_type_value.value();
 
-  if (maybe_type_value.value()->GetFields().size() != node->names.size()) {
+  if (type_value->GetFields().size() != node->names.size()) {
     error_handling::HandleTypecheckError("Mismatched field count in tuple variable definition", node->base);
   }
 
   if (!is_const_definition_.has_value()) {
-    error_handling::HandleInternalError("No value in is_const_definition_", "TypeCheckVisitor.TupleName");
+    error_handling::HandleInternalError("No value in is_const_definition_",
+                                        "TypeCheckVisitor.TupleName",
+                                        &node->base);
   }
 
   utils::ValueType value_type = context_manager_.GetValueType(type);
@@ -1040,7 +1074,7 @@ void TypeCheckVisitor::Visit(TupleName* node) {
   }
 
   for (size_t i = 0; i < node->names.size(); ++i) {
-    current_type_ = maybe_type_value.value()->GetFields()[i].second;
+    current_type_ = type_value->GetFields()[i].second;
 
     if (value_type == utils::ValueType::Tmp) { // TODO: ??
       current_type_ = context_manager_.ToModifiedValue(current_type_, utils::ValueType::Tmp);
@@ -1062,18 +1096,20 @@ void TypeCheckVisitor::Visit(VariantName* node) {
     type = maybe_defined_type_value.value()->GetType();
   }
 
-  std::optional<info::type::VariantType*> maybe_type_value = context_manager_.GetValue<info::type::VariantType>(type);
-
+  auto maybe_type_value = context_manager_.GetValue<info::type::VariantType>(type);
   if (!maybe_type_value.has_value()) {
     error_handling::HandleTypecheckError("Mismatched types in variant variable definition", node->base);
   }
+  info::type::VariantType* type_value = maybe_type_value.value();
 
-  if (maybe_type_value.value()->GetConstructors().size() != node->names.size()) {
+  if (type_value->GetConstructors().size() != node->names.size()) {
     error_handling::HandleTypecheckError("Mismatched variant count in variant variable definition", node->base);
   }
 
   if (!is_const_definition_.has_value()) {
-    error_handling::HandleInternalError("No value in is_const_definition_", "TypeCheckVisitor.VariantName");
+    error_handling::HandleInternalError("No value in is_const_definition_",
+                                        "TypeCheckVisitor.VariantName",
+                                        &node->base);
   }
 
   utils::ValueType value_type = context_manager_.GetValueType(type);
@@ -1083,14 +1119,14 @@ void TypeCheckVisitor::Visit(VariantName* node) {
   }
 
   for (size_t i = 0; i < node->names.size(); ++i) {
-    if (maybe_type_value.value()->GetConstructors()[i].GetFields().empty()) {
+    if (type_value->GetConstructors()[i].GetFields().empty()) {
       current_type_ = context_manager_.AddValue(
         info::type::OptionalType(
           context_manager_.AddValue(info::type::InternalType::Unit, utils::ValueType::Tmp),
           context_manager_.GetValueManager()),
         utils::IsConstModifierToValueType(is_const_definition_.value())); // TODO ??
     } else {
-      info::type::TupleType constructor_type_value = maybe_type_value.value()->GetConstructors()[i];
+      info::type::TupleType constructor_type_value = type_value->GetConstructors()[i];
 
       utils::IdType constructor_type =
         context_manager_.AddValue(std::move(constructor_type_value),
@@ -1113,7 +1149,8 @@ void TypeCheckVisitor::Visit(AnnotatedName* node) {
 
   if (!is_const_definition_.has_value()) {
     error_handling::HandleInternalError("No value in is_const_definition_",
-                                        "TypeCheckVisitor.AnnotatedName");
+                                        "TypeCheckVisitor.AnnotatedName",
+                                        &node->base);
   }
 
   utils::ValueType value_type = context_manager_.GetValueType(type);
@@ -1190,7 +1227,9 @@ void TypeCheckVisitor::Visit(VariantType* node) {
       Visit(std::get<std::unique_ptr<TupleType>>(constructor).get());
       std::optional<info::type::TupleType*> maybe_constructor = context_manager_.GetValue<info::type::TupleType>(current_type_);
       if (!maybe_constructor.has_value()) {
-        error_handling::HandleInternalError("Entity of VariantType is not TupleType", "TypeCheckVisitor.VariantType");
+        error_handling::HandleInternalError("Entity of VariantType is not TupleType",
+                                            "TypeCheckVisitor.VariantType",
+                                            &node->base);
       }
       constructors.push_back(*maybe_constructor.value());
     } else {
@@ -1222,7 +1261,7 @@ void TypeCheckVisitor::Visit(TypeExpression* node) {
         utils::ValueType::Tmp);
   } else {
     std::optional<utils::IdType> maybe_local_abstract_type =
-      context_manager_.GetLocalType(node->type.type);
+      context_manager_.FindLocalType(node->type.type);
     if (node->path.empty() && maybe_local_abstract_type.has_value()) {
       current_type_ = maybe_local_abstract_type.value();
     } else if (node->type.type_id_.has_value()) { // TODO: check that names are different (always true ??)
@@ -1230,7 +1269,9 @@ void TypeCheckVisitor::Visit(TypeExpression* node) {
         global_info_.GetTypeInfo<info::definition::AnyType>(node->type.type_id_.value());
 
       if (!maybe_type_info.has_value()) {
-        error_handling::HandleInternalError("No AnyType found (alias types, ... not implemented)", "TypeCheckVisitor.TypeExpression");
+        error_handling::HandleInternalError("No AnyType found (alias types, ... not implemented)",
+                                            "TypeCheckVisitor.TypeExpression",
+                                            &node->base);
       }
 
       Visitor::Visit(*maybe_type_info.value()->value);
@@ -1270,11 +1311,13 @@ void TypeCheckVisitor::Visit(ExtendedScopedAnyType* node) {
 void TypeCheckVisitor::Visit(ParametrizedTypeclass* node) {
   if (node->parameters.size()) {
     error_handling::HandleInternalError("Typeclasses with parameters are not implemented",
-                                        "TypeCheckVisitor.ParametrizedTypeclass");
+                                        "TypeCheckVisitor.ParametrizedTypeclass",
+                                        &node->base);
   }
 
   error_handling::HandleInternalError("ParametizedTypeclass shouldn't be visited (?)",
-                                      "TypeCheckVisitor.ParametrizedTypeclass");
+                                      "TypeCheckVisitor.ParametrizedTypeclass",
+                                      &node->base);
 }
 
 // Typeclass & Type -----------------
@@ -1331,7 +1374,9 @@ void TypeCheckVisitor::CollectTypeContext(const ParametrizedType& type,
     global_info_.GetTypeInfo<info::definition::AnyType>(type.type_id_.value());
 
   if (!maybe_type_info.has_value()) {
-    error_handling::HandleInternalError("Wrong type id", "TypeCheckVisitor.CollectTypeContext");
+    error_handling::HandleInternalError("Wrong type id",
+                                        "TypeCheckVisitor.CollectTypeContext",
+                                        std::nullopt);
   }
 
   info::definition::AnyType& type_info = *maybe_type_info.value();
@@ -1344,7 +1389,9 @@ void TypeCheckVisitor::CollectTypeContext(const ParametrizedType& type,
     Visit(type.parameters[i].get());
 
     if (context.count(type_info.parameters[i].type) != 0) {
-      error_handling::HandleInternalError("Same parameter type names", "TypeCheckVisitor.CollectTypeContext");
+      error_handling::HandleInternalError("Same parameter type names",
+                                          "TypeCheckVisitor.CollectTypeContext",
+                                          std::nullopt);
     }
 
     context[type_info.parameters[i].type] = current_type_;
@@ -1415,7 +1462,8 @@ std::optional<FunctionDeclaration*>
     auto maybe_type_info = global_info_.GetTypeInfo<info::definition::AnyType>(type_id);
     if (!maybe_type_info.has_value()) {
       error_handling::HandleInternalError("Functions / Methods implemented only for AnyType",
-                                          "TypeCheckVisitor.FunctionCallExpresssion");
+                                          "TypeCheckVisitor.FunctionCallExpresssion",
+                                          &node->base);
     }
     info::definition::AnyType* type_info = maybe_type_info.value();
 
@@ -1438,7 +1486,7 @@ std::optional<FunctionDeclaration*>
     error_handling::HandleTypecheckError("Can't call function from array type namespace", node->base);
   }
 
-  std::optional<utils::IdType> maybe_local_abstract_type = context_manager_.GetLocalType(type_node->type.type);
+  std::optional<utils::IdType> maybe_local_abstract_type = context_manager_.FindLocalType(type_node->type.type);
 
   if (maybe_local_abstract_type.has_value()) {
     auto maybe_abstract_type_info =
@@ -1446,7 +1494,8 @@ std::optional<FunctionDeclaration*>
 
     if (!maybe_abstract_type_info.has_value()) {
       error_handling::HandleInternalError("Local abstract type contains not abstract type",
-                                          "TypeCheckVisitor.FindTypeFunctionAndUpdate");
+                                          "TypeCheckVisitor.FindTypeFunctionAndUpdate",
+                                          &node->base);
     }
 
     maybe_function_declaration = FindAbstractTypeTypeclassFunctionAndUpdate(node,
@@ -1467,7 +1516,8 @@ std::optional<FunctionDeclaration*>
       auto maybe_type_info = global_info_.GetTypeInfo<info::definition::AnyType>(type_node->type_id_.value());
       if (!maybe_type_info.has_value()) {
         error_handling::HandleInternalError("typeclass functions / methods implemented only for AnyType",
-                                            "TypeCheckVisitor.FindTypeFunctionAndUpdate");
+                                            "TypeCheckVisitor.FindTypeFunctionAndUpdate",
+                                            &node->base);
       }
 
       maybe_function_declaration = FindDefinedTypeFunctionAndUpdate(node,
@@ -1478,8 +1528,14 @@ std::optional<FunctionDeclaration*>
 
       if (maybe_function_id.has_value()) {
         node->function_id_ = maybe_function_id.value();
+
+        auto maybe_function_declaration_info =
+          global_info_.GetFunctionInfo(maybe_function_id.value()).declaration;
+
         maybe_function_declaration =
-          global_info_.GetFunctionInfo(maybe_function_id.value()).declaration.value().node;
+          (maybe_function_declaration_info.has_value()
+            ? maybe_function_declaration_info.value().node
+            : std::optional<FunctionDeclaration*>());
       }
     }
   }
@@ -1496,19 +1552,21 @@ std::optional<FunctionDeclaration*> TypeCheckVisitor::FindFunctionAndUpdate(Func
       auto maybe_type_info = global_info_.GetTypeInfo<info::definition::AnyType>(path_types[i].value());
       if (!maybe_type_info.has_value()) {
         error_handling::HandleInternalError("typeclass functions / methods implemented only for AnyType",
-                                            "TypeCheckVisitor.FindTypeFunctionAndUpdate");
+                                            "TypeCheckVisitor.FindTypeFunctionAndUpdate",
+                                            &node->base);
       }
 
       maybe_function_declaration =
         FindDefinedTypeFunctionAndUpdate(node,
-                                        maybe_type_info.value(),
-                                        false);
-    } else {
+                                         maybe_type_info.value(),
+                                         false);
+    } else if (global_info_.GetNamespaceInfo(path_namespaces[i]).modifier == utils::ClassInternalsModifier::Static) {
       auto function_iter = global_info_.GetNamespaceInfo(path_namespaces[i]).functions.find(node->name);
       if (function_iter != global_info_.GetNamespaceInfo(path_namespaces[i]).functions.end()) {
         auto& maybe_declaration_info = global_info_.GetFunctionInfo(function_iter->second).declaration;
 
         if (maybe_declaration_info.has_value()) {
+          node->function_id_ = function_iter->second;
           maybe_function_declaration = maybe_declaration_info.value().node;
         }
       }
@@ -1540,7 +1598,6 @@ std::optional<FunctionDeclaration*>
   auto maybe_typeclass_graph_id = typeclass_graph_.FindFunctionTypeclass(node->name);
   if (!maybe_typeclass_graph_id.has_value()) {
     return std::nullopt;
-    // error_handling::HandleTypecheckError("Typeclass function not found", node->base);
   }
 
   auto maybe_typeclass_function_info = typeclass_graph_.GetFunctionInfo(node->name,
@@ -1552,15 +1609,17 @@ std::optional<FunctionDeclaration*>
 
   if (!maybe_typeclass_function_info.has_value()) {
     error_handling::HandleInternalError("Typeclass function info found, but typeclass id not found (abstract type)",
-                                        "TypeCheckVisitor.FindAbstractTypeTypeclassFunctionAndUpdate");
+                                        "TypeCheckVisitor.FindAbstractTypeTypeclassFunctionAndUpdate",
+                                        &node->base);
   }
 
-  // TODO: check that const functions not called on var expressions
+  // TODO: check that const functions not called on var expressions ??
   if ((maybe_typeclass_function_info.value()->modifier != utils::ClassInternalsModifier::Static) != is_method) {
     error_handling::HandleTypecheckError("Typeclass function has wrong modifier (abstract type)", node->base);
   }
 
   node->graph_id_ = maybe_typeclass_graph_id;
+  node->abstract_type_name_ = abstract_type_info->GetName();
   maybe_function_declaration = maybe_typeclass_function_info.value()->declaration;
 
   return maybe_function_declaration;
@@ -1580,10 +1639,53 @@ std::optional<FunctionDeclaration*>
     // error_handling::HandleTypecheckError("Function is not declared in type", node->base);
   }
 
+  // TODO: check that const functions not called on var expressions ??
+  if ((maybe_type_function_info.value()->modifier != utils::ClassInternalsModifier::Static) != is_method) {
+    error_handling::HandleTypecheckError("Typeclass function has wrong modifier (abstract type)", node->base);
+  }
+
   node->graph_id_ = defined_type->type.node->graph_id_;
+  // type defined -> abstract type name not needed
   maybe_function_declaration = maybe_type_function_info.value()->declaration;
 
   return maybe_function_declaration;
 }
 
+//
+
+bool TypeCheckVisitor::HandleBuiltinFunctionCall(FunctionCallExpression* node) {
+  if (node->name == "print") {
+    if (node->prefix.has_value()
+        || !node->parameters.empty()
+        || node->arguments.size() != 1) {
+      error_handling::HandleTypecheckError("Wrong builtin function \"print\" usage", node->base);
+    }
+
+    Visitor::Visit(node->arguments[0]);
+    if (!context_manager_.EqualValues(
+          current_type_,
+          context_manager_.AddValue(info::type::InternalType::String, utils::ValueType::Tmp))) {
+      error_handling::HandleTypecheckError("Wrong builtin function \"print\" argument (should be string)", node->base);
+    }
+
+    current_type_ = context_manager_.AddValue(info::type::InternalType::Unit, utils::ValueType::Tmp);
+    return true;
+  } else if (node->name == "read") {
+    if (node->prefix.has_value()
+        || !node->parameters.empty()
+        || node->arguments.size() != 0) {
+      error_handling::HandleTypecheckError("Wrong builtin function \"read\" usage", node->base);
+    }
+
+    current_type_ = context_manager_.AddValue(info::type::InternalType::String, utils::ValueType::Tmp);
+    return true;
+  }
+
+  return false;
+}
+
+bool TypeCheckVisitor::HandleBuiltinTypeclassFunctionCall(FunctionCallExpression*) {
+  return false;
+}
+
 } // namespace interpreter
diff --git a/tests/test_code.lang b/tests/test_code.lang
index d7e702f..6d743b1 100644
--- a/tests/test_code.lang
+++ b/tests/test_code.lang
@@ -76,11 +76,11 @@ namespace var Ord {
 
 //
 
-typeclass Show =
-  & var show : -> String
-
-typeclass Read =
-  & var read : String -> Read
+// typeclass Print =
+//   & var print : -> String
+//
+// typeclass Read =
+//   & var read : String -> Read
 
 typeclass Debug =
   & debug : -> String
@@ -132,6 +132,7 @@ decl ( -- ) : Int -> Int -> Int_0
 // }
 
 decl print : String -> Unit
+decl read : -> String
 
 decl func : String -> Int
 def func : s = {
@@ -140,5 +141,6 @@ def func : s = {
 }
 
 exec main {
-  for i in 0--10 do func: "abacaba"
+  for i in (,0 ,1 ,2 ,3) do func: "abacaba"
+  ; print: ({ return read: })
 }