diff --git a/include/execute_visitor.hpp b/include/execute_visitor.hpp
index 0d1da6e..9ee72c0 100644
--- a/include/execute_visitor.hpp
+++ b/include/execute_visitor.hpp
@@ -31,6 +31,11 @@ public:
   };
 
   void ExecutePartition(interpreter::tokens::PartitionStatement* partition) {
+    for (size_t i = 0; i < info::type::InternalTypesCount; ++i) {
+      info::type::InternalType type = static_cast<info::type::InternalType>(i);
+      std::string type_name = info::type::ToString(type);
+      context_manager_.DefineLocalType(type_name, global_info_.FindAbstractType(type_name).value()->node->type->graph_id_);
+    }
     Visit(partition);
   }
 
diff --git a/include/global_info.hpp b/include/global_info.hpp
index fe95619..dbc94e1 100644
--- a/include/global_info.hpp
+++ b/include/global_info.hpp
@@ -93,8 +93,6 @@ public:
 
     std::optional<utils::IdType> FindLocalTypeId(const std::string& type);
 
-    std::optional<utils::IdType> FindAbstractTypeId(const std::string& abstract_type);
-
     std::optional<utils::IdType> FindTypeclassId(const std::string& typeclass);
 
     std::optional<utils::IdType> FindConstructorId(const std::optional<std::vector<std::string>>& path,
@@ -164,14 +162,6 @@ public:
       return global_info_.GetTypeInfo<T>(id.value());
     }
 
-    std::optional<definition::AbstractType*> FindAbstractType(const std::string& abstract_type) {
-      std::optional<utils::IdType> id = FindAbstractTypeId(abstract_type);
-      if (!id.has_value()) {
-        return std::nullopt;
-      }
-      return &global_info_.GetAbstractTypeInfo(id.value());
-    }
-
     std::optional<definition::Typeclass*> FindTypeclass(const std::string& typeclass) {
       std::optional<utils::IdType> id = FindTypeclassId(typeclass);
       if (!id.has_value()) {
@@ -368,6 +358,16 @@ public:
   // function declarations & definitions should be added latter
   std::optional<utils::IdType> AddAnnotatedTypeToGraph(interpreter::tokens::AnnotatedType* node);
 
+  std::optional<utils::IdType> FindAbstractTypeId(const std::string& abstract_type);
+
+  std::optional<definition::AbstractType*> FindAbstractType(const std::string& abstract_type) {
+    std::optional<utils::IdType> id = FindAbstractTypeId(abstract_type);
+    if (!id.has_value()) {
+      return std::nullopt;
+    }
+    return &GetAbstractTypeInfo(id.value());
+  }
+
 private:
   void CollectFunctionInfo(
     utils::IdType current_namespace,
diff --git a/include/interpreter_tree.hpp b/include/interpreter_tree.hpp
index 62918d8..26e22bd 100644
--- a/include/interpreter_tree.hpp
+++ b/include/interpreter_tree.hpp
@@ -654,6 +654,7 @@ struct TypeExpression {
   ParametrizedType type;
 
   std::optional<size_t> array_size; // if array; 0 - dynamic size
+  bool is_optional = false; // for optionals
 
   std::optional<utils::IdType> type_id_;
   std::optional<utils::IdType> constructor_id_;
diff --git a/include/type_check_visitor.hpp b/include/type_check_visitor.hpp
index f77f197..2746a8b 100644
--- a/include/type_check_visitor.hpp
+++ b/include/type_check_visitor.hpp
@@ -27,7 +27,7 @@ public:
     // init internal type abstrac types
     for (size_t i = 0; i < info::type::InternalTypesCount; ++i) {
       info::type::InternalType type = static_cast<info::type::InternalType>(i);
-      Visit(namespace_visitor_.FindAbstractType(info::type::ToString(type)).value()->node);
+      Visit(global_info_.FindAbstractType(info::type::ToString(type)).value()->node);
     }
 
     Visit(source_file);
diff --git a/lang-parser b/lang-parser
index ddb08e9..5346d00 160000
--- a/lang-parser
+++ b/lang-parser
@@ -1 +1 @@
-Subproject commit ddb08e9b65123324800d1126d38764764363c0e5
+Subproject commit 5346d008497d93d30db4933dc3744b3de35cebf8
diff --git a/src/.link_symbols_visitor.cpp.kate-swp b/src/.link_symbols_visitor.cpp.kate-swp
new file mode 100644
index 0000000..aabc743
Binary files /dev/null and b/src/.link_symbols_visitor.cpp.kate-swp differ
diff --git a/src/build_visitor.cpp b/src/build_visitor.cpp
index 7a4219c..1023303 100644
--- a/src/build_visitor.cpp
+++ b/src/build_visitor.cpp
@@ -53,19 +53,11 @@ void BuildVisitor::Visit(Namespace* node) {
 
   auto parse_node = current_node_;
 
-  size_t child_count = parse_node.ChildCount();
-
-  if (child_count > 3) { // "namespace", ["var"/"const",] type, scope
-    std::string modifier = parse_node.NthChild(1).GetValue();
-    if (modifier == "const") {
-      node->modifier = utils::ClassInternalsModifier::Const;
-    } else if (modifier == "var") {
-      node->modifier = utils::ClassInternalsModifier::Var;
-    } else {
-      error_handling::HandleInternalError("Can't parse namespace modifier",
-                                          "BuildVisitor.Namespace",
-                                          &node->base);
-    }
+  std::string modifier = parse_node.NthChild(1).GetValue();
+  if (modifier == "const") {
+    node->modifier = utils::ClassInternalsModifier::Const;
+  } else if (modifier == "var") {
+    node->modifier = utils::ClassInternalsModifier::Var;
   } else {
     node->modifier = utils::ClassInternalsModifier::Static;
   }
@@ -1380,17 +1372,50 @@ void BuildVisitor::Visit(TypeExpression* node) {
   Visit(&node->type);
   ++excluded_child_count;
 
-  current_node_ = current_node_.NextSibling();
+  auto suffix_node1 = current_node_.NextSibling();
 
-  if (!current_node_.IsNull()) {
-    current_node_ = current_node_.NextSibling();
-    if (!current_node_.IsNull()) {
-      NumberLiteral literal;
-      Visit(&literal);
-      node->array_size = literal.value;
-      ++excluded_child_count;
+  // TODO: better structure // TODO: check
+  if (!suffix_node1.IsNull()) {
+    auto suffix_node2 = suffix_node1.NextSibling();
+    if (!suffix_node2.IsNull()) {
+      auto suffix_node3 = suffix_node2.NextSibling();
+      if (!suffix_node3.IsNull()) {
+        current_node_ = suffix_node2;
+
+        NumberLiteral literal;
+        Visit(&literal);
+        node->array_size = literal.value;
+        ++excluded_child_count;
+
+        node->is_optional = true;
+      } else {
+        if (suffix_node1.GetValue() == "_" && suffix_node2.GetValue() == "!") {
+          node->array_size = 0;
+
+          node->is_optional = true;
+        } else if (suffix_node1.GetValue() == "_") {
+          current_node_ = suffix_node2;
+
+          NumberLiteral literal;
+          Visit(&literal);
+          node->array_size = literal.value;
+          ++excluded_child_count;
+        } else {
+          error_handling::HandleInternalError("Undefined suffix (2 elements)",
+                                              "BuildVisitor.TypeExpression",
+                                              std::nullopt);
+        }
+      }
     } else {
-      node->array_size = 0;
+      if (suffix_node1.GetValue() == "_") {
+        node->array_size = 0;
+      } else if (suffix_node1.GetValue() == "!") {
+        node->is_optional = true;
+      } else {
+        error_handling::HandleInternalError("Undefined suffix (1 element)",
+                                            "BuildVisitor.TypeExpression",
+                                            std::nullopt);
+      }
     }
   }
 
diff --git a/src/global_info.cpp b/src/global_info.cpp
index 7a71961..ec1481e 100644
--- a/src/global_info.cpp
+++ b/src/global_info.cpp
@@ -235,7 +235,7 @@ utils::IdType GlobalInfo::NamespaceVisitor::AddAbstractType(const std::string& a
   //   error_handling::HandleNamesError("Can't redefine basic type as abstract type", base_node);
   // }
 
-  if (FindAbstractType(abstract_type).has_value()) {
+  if (global_info_.FindAbstractType(abstract_type).has_value()) {
     error_handling::HandleNamesError("More then one abstract type with the same name in namespace", base_node);
   }
 
@@ -385,16 +385,6 @@ std::optional<utils::IdType> GlobalInfo::NamespaceVisitor::FindLocalTypeId(const
   return std::nullopt;
 }
 
-std::optional<utils::IdType> GlobalInfo::NamespaceVisitor::FindAbstractTypeId(const std::string& abstract_type) {
-  auto abstract_type_id_iter = global_info_.name_to_abstract_type_.find(abstract_type);
-
-  if (abstract_type_id_iter != global_info_.name_to_abstract_type_.end()) {
-    return abstract_type_id_iter->second;
-  }
-
-  return std::nullopt;
-}
-
 std::optional<utils::IdType> GlobalInfo::NamespaceVisitor::FindTypeclassId(const std::string& typeclass) {
   auto typeclass_id_iter = global_info_.name_to_typeclass_.find(typeclass);
 
@@ -578,6 +568,16 @@ std::optional<utils::IdType> GlobalInfo::AddAnnotatedTypeToGraph(interpreter::to
                                     TypeclassGraph::Modifier::Type);
 }
 
+std::optional<utils::IdType> GlobalInfo::FindAbstractTypeId(const std::string& abstract_type) {
+  auto abstract_type_id_iter = name_to_abstract_type_.find(abstract_type);
+
+  if (abstract_type_id_iter != name_to_abstract_type_.end()) {
+    return abstract_type_id_iter->second;
+  }
+
+  return std::nullopt;
+}
+
 void GlobalInfo::CollectFunctionInfo(
     utils::IdType current_namespace,
     utils::ClassInternalsModifier modifier,
diff --git a/src/link_symbols_visitor.cpp b/src/link_symbols_visitor.cpp
index 37454fc..46fe1e6 100644
--- a/src/link_symbols_visitor.cpp
+++ b/src/link_symbols_visitor.cpp
@@ -134,7 +134,7 @@ void LinkSymbolsVisitor::Visit(TypeExpression* node) {
   if (maybe_type_namespace.has_value()) {
     info::definition::Namespace* type_namespace = maybe_type_namespace.value();
 
-    for (ssize_t i = (ssize_t)node->path.size(); i >= 0; --i) {
+    for (ssize_t i = (ssize_t)node->path.size() - 1; i >= 0; --i) {
       info::definition::Namespace* parent_namespace = &global_info_.GetNamespaceInfo(type_namespace->parent_namespace);
 
       auto type_iter = parent_namespace->types.find(type_namespace->type_name);
diff --git a/src/print_visitor.cpp b/src/print_visitor.cpp
index 077d233..5fb9861 100644
--- a/src/print_visitor.cpp
+++ b/src/print_visitor.cpp
@@ -654,10 +654,14 @@ void PrintVisitor::Visit(VariantType* node) {
 }
 
 void PrintVisitor::Visit(TypeExpression* node) {
-  out_ << "[TypeExpression ";
+  out_ << "[TypeExpression";
 
   if (node->array_size.has_value()) {
-    out_ << "[array size: " << node->array_size.value() << ']';
+    out_ << " [array size: " << node->array_size.value() << ']';
+  }
+
+  if (node->is_optional) {
+    out_ << " [optional]";
   }
 
   out_ << "] (";
diff --git a/src/type_check_visitor.cpp b/src/type_check_visitor.cpp
index 74087e7..c01835c 100644
--- a/src/type_check_visitor.cpp
+++ b/src/type_check_visitor.cpp
@@ -249,8 +249,6 @@ void TypeCheckVisitor::Visit(FunctionDefinitionStatement* node) {
     returned_type_ = current_type_;
   }
   if (!context_manager_.EqualValues(returned_type, returned_type_.value())) {
-    error_handling::DebugPrint(context_manager_.GetAnyValue(returned_type)->ToString());
-    error_handling::DebugPrint(context_manager_.GetAnyValue(returned_type_.value())->ToString());
     error_handling::HandleTypecheckError("Wrong function return type", node->base);
   }
   returned_type_ = std::nullopt;
@@ -284,7 +282,7 @@ void TypeCheckVisitor::Visit(TypeDefinitionStatement* node) {
     auto function_iter = type_functions.find(function.first);
 
     if (function_iter == type_functions.end() || !global_info_.GetFunctionInfo(function_iter->second).definition.has_value()) {
-      error_handling::HandleTypecheckError("Type is not satisfy typeclass requirements: " + function.first + " is not defined", node->base);
+      error_handling::HandleTypecheckError("Type not define all required functions: " + function.first + " is not defined", node->base);
     }
   }
 
@@ -1281,35 +1279,24 @@ void TypeCheckVisitor::Visit(TypeExpression* node) {
   std::unordered_map<std::string, utils::IdType> context;
   CollectTypeExpressionContext(*node, context);
 
-  // TODO: -------- remove, unneeded ------
-  // auto maybe_internal_type = info::type::ToInternalType(node->type.type);
-  //
-  // if (maybe_internal_type.has_value()) { // TODO: ???
-  //   // checks made in link_symbols_visitor
-  //   current_type_ =
-  //     context_manager_.AddValue<info::type::InternalType>(
-  //       maybe_internal_type.value(),
-  //       utils::ValueType::Tmp);
-  // } else {
-    std::optional<utils::IdType> maybe_local_abstract_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 ??)
-      std::optional<info::definition::AnyType*> maybe_type_info =
-        global_info_.GetTypeInfo<info::definition::AnyType>(node->type.type_id_.value());
+  std::optional<utils::IdType> maybe_local_abstract_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 ??)
+    std::optional<info::definition::AnyType*> maybe_type_info =
+      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",
-                                            &node->base);
-      }
-
-      VisitDefinedType(maybe_type_info.value(), context);
-    } else {
-      error_handling::HandleTypecheckError("Type not found", node->base);
+    if (!maybe_type_info.has_value()) {
+      error_handling::HandleInternalError("No AnyType found (alias types, ... not implemented)",
+                                          "TypeCheckVisitor.TypeExpression",
+                                          &node->base);
     }
-  // }
+
+    VisitDefinedType(maybe_type_info.value(), context);
+  } else {
+    error_handling::HandleTypecheckError("Type not found", node->base);
+  }
 
   if (node->array_size.has_value()) {
     current_type_ = context_manager_.AddValue(
@@ -1317,6 +1304,12 @@ void TypeCheckVisitor::Visit(TypeExpression* node) {
       utils::ValueType::Tmp);
   }
 
+  if (node->is_optional) {
+    current_type_ = context_manager_.AddValue(
+      info::type::OptionalType(current_type_, context_manager_.GetValueManager()),
+      utils::ValueType::Tmp);
+  }
+
   node->base.type_ = current_type_;
 }
 
@@ -1433,7 +1426,10 @@ void TypeCheckVisitor::CollectTypeExpressionContext(const TypeExpression& type_e
 utils::IdType TypeCheckVisitor::TypeInContext(utils::IdType type,
                                               const std::unordered_map<std::string, utils::IdType>& context) {
   info::type::Type type_in_context = *context_manager_.GetAnyValue(type);
-  type_in_context.InContext(context);
+  auto maybe_new_type = type_in_context.InContext(context);
+  if (maybe_new_type.has_value()) {
+    return maybe_new_type.value();
+  }
   return context_manager_.AddValue(std::move(type_in_context), utils::ValueType::Tmp);
 }
 
diff --git a/src/typed_print_visitor.cpp b/src/typed_print_visitor.cpp
index c92bc83..0a7204e 100644
--- a/src/typed_print_visitor.cpp
+++ b/src/typed_print_visitor.cpp
@@ -920,9 +920,13 @@ void TypedPrintVisitor::Visit(TypeExpression* node) {
     out_ << context_manager_.GetAnyValue(node->base.type_.value())->GetTypeName();
   }
 
-  out_ << ") ";
+  out_ << ")";
   if (node->array_size.has_value()) {
-    out_ << "[array size: " << node->array_size.value() << ']';
+    out_ << " [array size: " << node->array_size.value() << ']';
+  }
+
+  if (node->is_optional) {
+    out_ << " [optional]";
   }
 
   out_ << "] (";
diff --git a/tests/classes.lang b/tests/classes.lang
index bb8e32c..f3487b1 100644
--- a/tests/classes.lang
+++ b/tests/classes.lang
@@ -17,7 +17,7 @@ struct (Complex : #Value) =
 
 struct Task =
   & name : String
-  & duration : Float
+  & duration : Float!
 
 class Employee =
   & name : String
diff --git a/tests/test_code.lang b/tests/test_code.lang
index 191d028..01a3951 100644
--- a/tests/test_code.lang
+++ b/tests/test_code.lang
@@ -149,7 +149,7 @@ typeclass Show =
   & var show : -> String
 
 typeclass Read =
-  & var read : String -> Read
+  & read : String -> Read
 
 typeclass (Str : #Show #Read)
 
@@ -179,9 +179,11 @@ typeclass Enum =
 
 //
 
-decl print : String -> Unit
-decl scan : -> String
-decl random : -> Int // TODO
+namespace IO {
+  decl print : String -> Unit
+  decl scan : -> String
+  decl random : -> Int // TODO
+}
 
 //
 
@@ -211,19 +213,46 @@ def ( -- ) : begin end = {
   })
 }
 
-decl func : String -> Int -> Int
-def func : s i = {
-  ; print: s
-  var x = s
-  ; print: (i.show:)
-  return 5
-}
+// decl func : String -> Int -> Int
+// def func : s i = {
+//   ; print: s
+//   var x = s
+//   ; print: (i.show:)
+//   return 5
+// }
+//
+// exec main {
+//   for i in 0--19 do func: "a" (i * 2 +. 3)
+//   ; print: ({
+//     if true then bring scan: else { ; print: "aaa" }
+//     bring "nothing"
+//     ; print: "aaa"
+//   })
+// }
+
+decl scan_int : -> Int
+def scan_int = Int.read: (IO.scan:)
+
+decl print_int : Int -> Unit
+def print_int : x = IO.print: (x.show:)
+
+decl scan_anything ('A : #Read) : -> 'A
+def scan_anything = 'A.read: (IO.scan:)
+
+decl print_anything ('A : #Show) : 'A -> Unit
+def print_anything : x = IO.print: (x.show:)
+
+/*
+struct Array 'A = & data : 'A_0
+
+namespace Array {
+  decl construct : 'A_0 -> Array
+  def construct: x = $(Array 'A) & data = x
+} // TODO: construct decl + default def -> segfault
+*/
 
 exec main {
-  for i in 0--19 do func: "a" (i * 2 +. 3)
-  ; print: ({
-    if true then bring scan: else { ; print: "aaa" }
-    bring "nothing"
-    ; print: "aaa"
-  })
+  var n = scan_anything Int:
+  var a = for _ in 0--n do scan_int:
+  ; print_anything Int: n
 }