diff --git a/include/basic_nodes.hpp b/include/basic_nodes.hpp
index b96c57c..e952301 100644
--- a/include/basic_nodes.hpp
+++ b/include/basic_nodes.hpp
@@ -8,11 +8,11 @@
 namespace nodes {
 
 enum class Modifier {
-  OUT,       // -> x
-  IN,        // <- x
-  REF,       // <> x
-  OR_FALSE,  // x?
-  OR_RETURN, // x!
+  OUT,      // -> x
+  IN,       // <- x
+  REF,      // <> x
+  OPTIONAL, // x?
+  RESULT,   // x!
   NONE,
 };
 
diff --git a/include/name_tree.hpp b/include/name_tree.hpp
index f7b2ae1..5db7479 100644
--- a/include/name_tree.hpp
+++ b/include/name_tree.hpp
@@ -19,6 +19,8 @@ public:
 
   bool insert(const std::string &path, nodes::Statement &&statement);
 
+  bool insert(const std::string &path, const nodes::Statement &statement);
+
   std::optional<nodes::Statement *> find(const std::string &path);
 
   std::optional<const nodes::Statement *> find(const std::string &path) const;
@@ -48,6 +50,14 @@ private:
       return true;
     }
 
+    bool set_statement(const nodes::Statement &statement) {
+      if (statement_.has_value()) {
+        return false;
+      }
+      statement_ = statement;
+      return true;
+    }
+
     std::optional<size_t> find(size_t name_id) const {
       auto name_iter = children_.find(name_id);
 
diff --git a/include/statement_builders.hpp b/include/statement_builders.hpp
index 852ecd0..6cd88a4 100644
--- a/include/statement_builders.hpp
+++ b/include/statement_builders.hpp
@@ -1,5 +1,6 @@
 #pragma once
 
+#include "name_tree.hpp"
 #include "statement_nodes.hpp"
 #include "tree_sitter_wrapper.hpp"
 
@@ -7,14 +8,18 @@
 
 namespace builders {
 
+// statements (copies of statements  are in name_tree) returned to print /
+// translate them in required order
 std::vector<nodes::Statement>
 build_source_file(parser::ParseTree::Node parser_node,
                   nodes::ExpressionStorage &expression_storage,
-                  nodes::TypeStorage &type_storage);
+                  nodes::TypeStorage &type_storage, names::NameTree &name_tree);
 
+// copy of statement inserted into name_tree
 nodes::Statement build_statement(parser::ParseTree::Node parser_node,
                                  nodes::ExpressionStorage &expression_storage,
-                                 nodes::TypeStorage &type_storage);
+                                 nodes::TypeStorage &type_storage,
+                                 names::NameTree &name_tree);
 
 nodes::Import build_import(parser::ParseTree::Node parser_node);
 
diff --git a/include/statement_nodes.hpp b/include/statement_nodes.hpp
index c5b1735..85c0d86 100644
--- a/include/statement_nodes.hpp
+++ b/include/statement_nodes.hpp
@@ -464,6 +464,10 @@ private:
 
 class Statement {
 public:
+  Statement(const Statement &) = default;
+  Statement(Statement &&) = default;
+  Statement &operator=(const Statement &) = default;
+
   template <typename T>
   Statement(T &&statement) : expression_(std::forward<T>(statement)) {}
 
diff --git a/include/statement_printers.hpp b/include/statement_printers.hpp
index fe1f488..e8c34cb 100644
--- a/include/statement_printers.hpp
+++ b/include/statement_printers.hpp
@@ -1,6 +1,7 @@
 #pragma once
 
 #include "basic_printers.hpp"
+#include "name_tree.hpp"
 #include "statement_nodes.hpp"
 
 #include <vector>
diff --git a/src/basic_builders.cpp b/src/basic_builders.cpp
index 8105320..d8d136c 100644
--- a/src/basic_builders.cpp
+++ b/src/basic_builders.cpp
@@ -43,9 +43,9 @@ nodes::Modifier build_modifier(parser::ParseTree::Node parser_node) {
   std::string modifier = parser_node.get_value();
 
   if (modifier == "?") {
-    return nodes::Modifier::OR_FALSE;
+    return nodes::Modifier::OPTIONAL;
   } else if (modifier == "!") {
-    return nodes::Modifier::OR_RETURN;
+    return nodes::Modifier::RESULT;
   } else if (modifier == "->" || modifier == "out") {
     return nodes::Modifier::OUT;
   } else if (modifier == "<-" || modifier == "in") {
diff --git a/src/basic_printers.cpp b/src/basic_printers.cpp
index bf2647c..7018b89 100644
--- a/src/basic_printers.cpp
+++ b/src/basic_printers.cpp
@@ -17,10 +17,10 @@ void print_modifier(const nodes::Modifier &modifier, Printer &printer) {
   case nodes::Modifier::REF:
     printer.print(printer.print_words_instead_of_symbols() ? "ref " : "<> ");
     break;
-  case nodes::Modifier::OR_FALSE:
+  case nodes::Modifier::OPTIONAL:
     printer.print("?");
     break;
-  case nodes::Modifier::OR_RETURN:
+  case nodes::Modifier::RESULT:
     printer.print("!");
     break;
   case nodes::Modifier::NONE:
diff --git a/src/expression_printers.cpp b/src/expression_printers.cpp
index 327ad02..05eade8 100644
--- a/src/expression_printers.cpp
+++ b/src/expression_printers.cpp
@@ -338,8 +338,8 @@ void print_modifier_expression(const nodes::ModifierExpression &expression,
 
   print_expression(*expression.get_expression(), printer);
 
-  if (expression.get_modifier() == nodes::Modifier::OR_FALSE ||
-      expression.get_modifier() == nodes::Modifier::OR_RETURN) {
+  if (expression.get_modifier() == nodes::Modifier::OPTIONAL ||
+      expression.get_modifier() == nodes::Modifier::RESULT) {
     print_modifier(expression.get_modifier(), printer);
   }
 }
diff --git a/src/main.cpp b/src/main.cpp
index 9cfe38c..2b35ad1 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -5,6 +5,7 @@
 #include "basic_printers.hpp"
 #include "error_handling.hpp"
 #include "expression_nodes.hpp"
+#include "name_tree.hpp"
 #include "statement_builders.hpp"
 #include "statement_printers.hpp"
 #include "type_nodes.hpp"
@@ -38,9 +39,10 @@ int main(int argc, char **argv) {
 
   nodes::ExpressionStorage expression_storage;
   nodes::TypeStorage type_storage;
+  names::NameTree name_tree;
 
   auto statements = builders::build_source_file(
-      parse_tree.get_root(), expression_storage, type_storage);
+      parse_tree.get_root(), expression_storage, type_storage, name_tree);
 
   printers::Printer printer(std::cout, 2, 80, false);
   printers::print_source_file(statements, printer);
diff --git a/src/name_tree.cpp b/src/name_tree.cpp
index 439fc2e..a0a9a3d 100644
--- a/src/name_tree.cpp
+++ b/src/name_tree.cpp
@@ -17,6 +17,20 @@ bool NameTree::insert(const std::string &path, nodes::Statement &&statement) {
   return true;
 }
 
+bool NameTree::insert(const std::string &path,
+                      const nodes::Statement &statement) {
+  auto name_ids = slice_path_to_name_ids(path);
+
+  size_t node_id = add_node(get_root(), name_ids);
+
+  if (nodes_[node_id].get_statement().has_value()) {
+    return false;
+  }
+
+  nodes_[node_id].set_statement(statement);
+  return true;
+}
+
 std::optional<nodes::Statement *> NameTree::find(const std::string &path) {
   auto name_ids = slice_path_to_existing_name_ids(path);
 
diff --git a/src/statement_builders.cpp b/src/statement_builders.cpp
index fb1a5b3..0a0b1af 100644
--- a/src/statement_builders.cpp
+++ b/src/statement_builders.cpp
@@ -11,6 +11,7 @@
 #include "tree_sitter_wrapper.hpp"
 #include "type_builders.hpp"
 #include "type_nodes.hpp"
+#include "utils.hpp"
 
 #include <optional>
 #include <type_traits>
@@ -22,13 +23,14 @@ namespace builders {
 std::vector<nodes::Statement>
 build_source_file(parser::ParseTree::Node parser_node,
                   nodes::ExpressionStorage &expression_storage,
-                  nodes::TypeStorage &type_storage) {
+                  nodes::TypeStorage &type_storage,
+                  names::NameTree &name_tree) {
   std::vector<nodes::Statement> statements;
 
   auto current_node = parser_node.nth_named_child(0);
   while (!current_node.is_null()) {
-    statements.push_back(
-        build_statement(current_node, expression_storage, type_storage));
+    statements.push_back(build_statement(current_node, expression_storage,
+                                         type_storage, name_tree));
     current_node = current_node.next_named_sibling();
   }
 
@@ -38,29 +40,70 @@ build_source_file(parser::ParseTree::Node parser_node,
 // import | type_definition | function_definition | typeclass_definition
 nodes::Statement build_statement(parser::ParseTree::Node parser_node,
                                  nodes::ExpressionStorage &expression_storage,
-                                 nodes::TypeStorage &type_storage) {
+                                 nodes::TypeStorage &type_storage,
+                                 names::NameTree &name_tree) {
   tokens::Type type = tokens::string_to_type(parser_node.get_type());
 
+  std::optional<std::string> statement_name;
+  std::optional<nodes::Statement> statement;
+
   switch (type) {
   case tokens::Type::IMPORT:
-    return nodes::Statement(build_import(parser_node));
+    statement = nodes::Statement(build_import(parser_node));
+    statement_name = *statement.value()
+                          .get<nodes::Import>()
+                          .value()
+                          ->get_module_name()
+                          ->get();
+    break;
   case tokens::Type::TYPE_DEFINITION:
-    return nodes::Statement(
+    statement = nodes::Statement(
         build_type_definition(parser_node, expression_storage, type_storage));
+    statement_name = *statement.value()
+                          .get<nodes::TypeDefinition>()
+                          .value()
+                          ->get_name()
+                          ->get();
+    break;
   case tokens::Type::FUNCTION_DEFINITION:
-    return nodes::Statement(build_function_definition(
+    statement = nodes::Statement(build_function_definition(
         parser_node, expression_storage, type_storage));
+    statement_name = *statement.value()
+                          .get<nodes::FunctionDefinition>()
+                          .value()
+                          ->get_name()
+                          ->get();
+    break;
   case tokens::Type::TYPECLASS_DEFINITION:
-    return nodes::Statement(build_typeclass_definition(
+    statement = nodes::Statement(build_typeclass_definition(
         parser_node, expression_storage, type_storage));
+    statement_name = *statement.value()
+                          .get<nodes::TypeclassDefinition>()
+                          .value()
+                          ->get_name()
+                          ->get();
+    break;
   case tokens::Type::EMPTY_LINES:
-    return nodes::Statement(build_empty_lines(parser_node));
+    statement = build_empty_lines(parser_node);
+    break;
   default:
     error_handling::handle_parsing_error("Unexprected statement node type",
                                          parser_node);
   }
-  error_handling::handle_general_error("Unreachable");
-  exit(1); // unreachable
+
+  if (!statement.has_value()) {
+    error_handling::handle_general_error("Unreachable");
+  }
+
+  if (statement_name.has_value()) {
+    // TODO: combine statements with same name
+    if (!name_tree.insert(statement_name.value(), statement.value())) {
+      error_handling::handle_parsing_error(
+          "Two or more statements in file have the same name", parser_node);
+    }
+  }
+
+  return std::move(statement.value());
 }
 
 // ('::' | 'import') simple_name ('=' simple_name)? (':' identifier*)?
@@ -272,8 +315,8 @@ build_function_definition(parser::ParseTree::Node parser_node,
         last_after_modifier = build_modifier(maybe_reference_node);
 
         // only optional, result allowed
-        if (last_after_modifier != nodes::Modifier::OR_FALSE &&
-            last_after_modifier != nodes::Modifier::OR_RETURN) {
+        if (last_after_modifier != nodes::Modifier::OPTIONAL &&
+            last_after_modifier != nodes::Modifier::RESULT) {
           last_after_modifier = nodes::Modifier::NONE;
         }
       }
diff --git a/src/statement_printers.cpp b/src/statement_printers.cpp
index 2f83478..922f942 100644
--- a/src/statement_printers.cpp
+++ b/src/statement_printers.cpp
@@ -4,6 +4,7 @@
 #include "doc_printers.hpp"
 #include "expression_nodes.hpp"
 #include "expression_printers.hpp"
+#include "statement_nodes.hpp"
 #include "type_printers.hpp"
 
 namespace printers {
diff --git a/src/type_builders.cpp b/src/type_builders.cpp
index 7982ff3..b9ddbe4 100644
--- a/src/type_builders.cpp
+++ b/src/type_builders.cpp
@@ -24,8 +24,8 @@ nodes::TypeProxy build_type(parser::ParseTree::Node parse_node,
     modifier = build_modifier(current_node);
 
     // only optional, result allowed
-    if (modifier != nodes::Modifier::OR_FALSE &&
-        modifier != nodes::Modifier::OR_RETURN) {
+    if (modifier != nodes::Modifier::OPTIONAL &&
+        modifier != nodes::Modifier::RESULT) {
       modifier = nodes::Modifier::NONE;
     }
   }
diff --git a/tests/test.langexp b/tests/test.langexp
index da5b29a..96c9b14 100644
--- a/tests/test.langexp
+++ b/tests/test.langexp
@@ -2,10 +2,10 @@
 
 :: module; // import module to current namespace
 
-:: _ = module; // import module to current namespace and use functions inside without namespace
+:: _ = module_2; // import module to current namespace and use functions inside without namespace
 
-:: module : func1 func2 func3;
-:: module_namespace = module;
+:: module_3 : func1 func2 func3;
+:: module_namespace = module_4;
 
 func = {
 
@@ -40,7 +40,7 @@ sum 'a? 'b? =
 : example that shows that default annotations are argument names (without ')
 @a is integer
 @b also integer
-sum 'a 'b = 'a + 'b;
+sum_2 'a 'b = 'a + 'b;
 
 : this function can be used to calculate Fibonacci sequence elements
 : it is important is some algorithmic tasks
@@ -137,7 +137,7 @@ bubble_sort 'arr : <> Array['A] = {
 }
 
 : bubble_sort with names instead of symbols
-bubble_sort 'arr : ref Array['A] = {
+bubble_sort_2 'arr : ref Array['A] = {
   var swap_occured := true;
   for swap_occured do {
     swap_occured = false;
@@ -151,9 +151,7 @@ bubble_sort 'arr : ref Array['A] = {
   & @key Key
   & @value Value
   & @left ^TreeNode['Key 'Value]
-  & @right ^TreeNode['Key 'Value];
-
-TreeNode {
+  & @right ^TreeNode['Key 'Value] {
   new = do_something; // static methods
 
   $insert 'key = do_something; // const methods
@@ -186,7 +184,7 @@ print_two 'a 'b = print 'a, print 'b;
 swap 'a 'b : <> 'A <> 'A = %c := <- 'a, 'a := <- 'b, 'b := <- c;
 
 : previous example with automatic type deduction
-swap <> 'a <> 'b = %c := <- 'a, 'a := <- 'b, 'b := <- c;
+swap_2 <> 'a <> 'b = %c := <- 'a, 'a := <- 'b, 'b := <- c;
 
 : several outputs example
 scan_three : -> String -> String -> String = scan & scan & scan;