diff --git a/comdel/domain/comdelgenerator.cpp b/comdel/domain/comdelgenerator.cpp
index 8c94cc6..8c57d06 100644
--- a/comdel/domain/comdelgenerator.cpp
+++ b/comdel/domain/comdelgenerator.cpp
@@ -58,6 +58,8 @@ Value toType(ValueNode node) {
         return Value::fromInt(node.asInt());
     } else if(node.getType() == ValueNode::STRING) {
         return Value::fromString(node.asString());
+    } else if(node.getType() == ValueNode::NIL) {
+        return Value::fromNull();
     }
     return Value::fromReference(node.asIdentifier(), Value::UNDEFINED);
 }
@@ -228,12 +230,12 @@ std::optional<Connection> ComdelGenerator::loadConnection(ConnectionNode node)
 
     auto componentInstance = getComponentPin(component, pin);
     if(!componentInstance) {
-        errors.push_back(SourceError(node.span, "pin does not exist"));
+        errors.emplace_back(node.span, "pin does not exist");
     }
 
     auto busInstance = getBus(bus);
     if(!busInstance) {
-        errors.push_back(SourceError(node.span, "bus does not exist"));
+        errors.emplace_back(node.span, "bus does not exist");
     }
 
     std::set<std::string> wireNames;
@@ -258,12 +260,20 @@ std::optional<Connection> ComdelGenerator::loadConnection(ConnectionNode node)
 
     std::vector<Value> wires;
     for(uint i=0; i<node.wires.size(); i++) {
-        if(attributeNames.count(node.wires[i].value)) {
-            wires.push_back(Value::fromReference(node.wires[i].value, Value::ATTRIBUTE_REFERENCE));
-        } else if(wireNames.count(node.wires[i].value)) {
-            wires.push_back(Value::fromReference(node.wires[i].value, Value::WIRE_REFERENCE));
+        if(node.wires[i].is(ValueNode::NIL)) {
+            wires.push_back(Value::fromNull());
+        } else if(node.wires[i].is(ValueNode::INT)) {
+             wires.push_back(Value::fromInt(node.wires[i].asInt()));
+        } else if(node.wires[i].is(ValueNode::IDENTIFIER)) {
+            if(attributeNames.count(node.wires[i].asIdentifier())) {
+                wires.push_back(Value::fromReference(node.wires[i].asIdentifier(), Value::ATTRIBUTE_REFERENCE));
+            } else if(wireNames.count(node.wires[i].asIdentifier())) {
+                wires.push_back(Value::fromReference(node.wires[i].asIdentifier(), Value::WIRE_REFERENCE));
+            } else {
+                errors.emplace_back(node.wires[i].span, "unknown identifier");
+            }
         } else {
-            errors.push_back(SourceError(node.wires[i].span, "unknown identifier"));
+            errors.emplace_back(node.wires[i].span, "unknown value type");
         }
     }
 
@@ -520,26 +530,34 @@ std::optional<Popup> ComdelGenerator::loadPopup(PopupNode node, std::string name
     std::vector<Enumeration> enumeration;
     if(node.enumerated) {
         for(uint i=0; i<node.enumeration.size(); i++) {
-            if(toType(node.enumeration[i].value.getType()) != type) {
+            if(type == Value::INT || type == Value::STRING || type == Value::BOOL) {
+                auto value = toType(node.enumeration[i].value);
+                if(value.getType() == type) {
+                    enumeration.push_back(Enumeration(node.enumeration[i].key.asString(), value));
+                } else {
+                    errors.push_back(SourceError{node.enumeration[i].span, "wrong type"});
+                }
+            } else if(type == Value::WIRE_REFERENCE) {
+                auto value = toType(node.enumeration[i].value);
+                if(value.isType(Value::UNDEFINED)) {
+                    if(current().doesWireExists(value.asReference())) {
+                        value = Value::fromReference(value.asReference(), Value::WIRE_REFERENCE);
+                    } else {
+                        errors.push_back(SourceError{node.enumeration[i].span, "unknown wire"});
+                    }
+                }
 
+                if(value.isType(Value::WIRE_REFERENCE) || value.isType(Value::INT) || value.isType(Value::NIL)) {
+                    enumeration.push_back(Enumeration(node.enumeration[i].key.asString(), value));
+                } else {
+                    errors.push_back(SourceError{node.enumeration[i].span, "wrong type"});
+                }
             }
-            auto value = toType(node.enumeration[i].value);
-
-            if(value.isType(Value::UNDEFINED) && current().doesWireExists(value.asReference())) {
-                value = Value::fromReference(value.asReference(), Value::WIRE_REFERENCE);
-            } else {
-                errors.push_back(SourceError{node.enumeration[i].span, "unknown wire"});
-            }
-            if(value.getType() != type) {
-                errors.push_back(SourceError{node.enumeration[i].span, "wrong type"});
-            }
-            enumeration.push_back(Enumeration(node.enumeration[i].key.asString(), value));
         }
     } else {
         if(type == Value::WIRE_REFERENCE && !current().inConnection) {
             errors.push_back(SourceError{node.span, "@enumeration is required for attributes of type wire"});
         }
-
     }
 
     pop();
diff --git a/comdel/domain/value.cpp b/comdel/domain/value.cpp
index 80ab71d..be56f6a 100644
--- a/comdel/domain/value.cpp
+++ b/comdel/domain/value.cpp
@@ -105,4 +105,10 @@ Value Value::ofType(Value::ValueType type) {
 
 }
 
+Value Value::fromNull() {
+    Value val;
+    val.type = Value::NIL;
+    return val;
+}
+
 } // namespace domain
diff --git a/comdel/domain/value.h b/comdel/domain/value.h
index eb3cedc..0241f64 100644
--- a/comdel/domain/value.h
+++ b/comdel/domain/value.h
@@ -19,6 +19,7 @@ public:
         ADDRESS_SPACE,
         ATTRIBUTE_REFERENCE,
         WIRE_REFERENCE,
+        NIL,
         UNDEFINED,
     };
 
@@ -54,6 +55,7 @@ public:
     static Value fromInt(long long value);
     static Value fromString(std::string value);
     static Value fromBool(bool value);
+    static Value fromNull();
     static Value fromAddressSpace(AddressSpace addressSpace);
     static Value fromReference(std::string value, ValueType type);
     static Value ofType(ValueType type);
diff --git a/comdel/parser/astnode.h b/comdel/parser/astnode.h
index 5f3df65..48950bf 100644
--- a/comdel/parser/astnode.h
+++ b/comdel/parser/astnode.h
@@ -74,7 +74,8 @@ public:
         STRING,
         BOOL,
         WIRE,
-        IDENTIFIER
+        IDENTIFIER,
+        NIL,
     };
 
 
@@ -148,6 +149,12 @@ public:
         return value;
     }
 
+    static ValueNode ofNull() {
+        ValueNode value;
+        value.type = NIL;
+        return value;
+    }
+
     static ValueNode ofWire(std::string _value) {
         ValueNode value;
         value.type = WIRE;
@@ -293,7 +300,7 @@ struct ConnectionNode: AstNode
     IdentifierNode pin;
     IdentifierNode bus;
     std::vector<AttributeNode> attributes;
-    std::vector<IdentifierNode> wires;
+    std::vector<ValueNode> wires;
 };
 
 
diff --git a/comdel/parser/comdellexer.cpp b/comdel/parser/comdellexer.cpp
index 6dd5311..e4c2032 100644
--- a/comdel/parser/comdellexer.cpp
+++ b/comdel/parser/comdellexer.cpp
@@ -21,7 +21,7 @@ inline bool identifierContinue(char ch) {
 }
 
 inline bool numberStart(char ch) {
-    return isdigit(ch);
+    return isdigit(ch) || ch == '-';
 }
 
 inline bool isWhitespace(char ch) {
@@ -64,10 +64,10 @@ LexerResult ComdelLexer::tokenize() {
 
         tokenType = from_token(text, tokenType.value());
 
-        tokens.push_back(Token(*tokenType, Span(tokenBegin, position), text));
+        tokens.emplace_back(*tokenType, Span(tokenBegin, position), text);
     }
 
-    tokens.push_back(Token( TokenType::END_OF_FILE, Span(position), ""));
+    tokens.emplace_back( TokenType::END_OF_FILE, Span(position), "");
 
     return LexerResult { tokens, errors };
 }
@@ -251,6 +251,9 @@ PResult<TokenType> ComdelLexer::nextTokenType() {
     }
     else if (numberStart(ch))
     {
+        if(ch == '-') {
+            bump();
+        }
         unsigned takenDigits;
         Radix radix = takeRadix();
         takenDigits = takeNumberInRadix(radix);
@@ -393,15 +396,6 @@ PResult<TokenType> ComdelLexer::nextTokenType() {
         bump();
         return TokenType::EQUALS;
     }
-    else if (ch == '<')
-    {
-        bump();
-        return TokenType::LT;
-    }
-    else if (ch == '>')
-    {
-        return TokenType::GT;
-    }
     else
     {
         std::stringstream message;
diff --git a/comdel/parser/comdelparser.cpp b/comdel/parser/comdelparser.cpp
index 1741e04..23129b9 100644
--- a/comdel/parser/comdelparser.cpp
+++ b/comdel/parser/comdelparser.cpp
@@ -711,8 +711,10 @@ PResult<AttributeNode> ComdelParser::parseAttribute() {
 
     if(attribute.type == ValueNode::BOOL) {
         if(check(TokenType::TRUE)) {
+            bump();
             attribute.defaultValue = ValueNode::ofBool(true);
         } else if(check(TokenType::FALSE)) {
+            bump();
             attribute.defaultValue = ValueNode::ofBool(false);
         } else {
             return unexpected();
@@ -742,7 +744,10 @@ PResult<AttributeNode> ComdelParser::parseAttribute() {
         if(check(TokenType::IDENTIFIER)) {
             auto identifier = parseIdentifier();
             attribute.defaultValue = ValueNode::ofWire(identifier->value);
-        }  else {
+        } else if(check(TokenType::NIL)) {
+            bump();
+            attribute.defaultValue = ValueNode::ofNull();
+        } else {
             return unexpected();
         }
     }
@@ -868,8 +873,8 @@ PResult<ConnectionNode> ComdelParser::parseConnection() {
             APPEND_OR_RETURN_IF_ERR(connection.attributes, parseAttribute());
         } else if(check(TokenType::KW_WIRES)) {
             bump();
-            auto wires = parseList<IdentifierNode>(std::optional<TokenType>(TokenType::LBRACE), TokenType::RBRACE, std::optional<TokenType>(TokenType::COMMA), false,
-                      [this] { return parseIdentifier(); });
+            auto wires = parseList<ValueNode>(std::optional<TokenType>(TokenType::LBRACE), TokenType::RBRACE, std::optional<TokenType>(TokenType::COMMA), false,
+                      [this] { return parseConnectionWire(); });
             RETURN_IF_ERR(wires);
             connection.wires = *wires;
         } else {
@@ -973,9 +978,14 @@ PResult<ValueNode> ComdelParser::parseValue() {
     } else if(check(TokenType::NUMBER)) {
         value = ValueNode::ofInt(parseNumber()->value);
     } else if(check(TokenType::TRUE)) {
+        bump();
         value = ValueNode::ofBool(true);
     } else if(check(TokenType::FALSE)) {
+        bump();
         value = ValueNode::ofBool(false);
+    } else if(check(TokenType::NIL)) {
+        bump();
+        value = ValueNode::ofNull();
     } else {
         return unexpected();
     }
@@ -1167,3 +1177,16 @@ PResult<ConnectionInstanceNode> ComdelParser::parseConnectionInstance() {
     return spanner(connection);
 }
 
+PResult<ValueNode> ComdelParser::parseConnectionWire() {
+    if(check(TokenType::NUMBER)) {
+        return ValueNode::ofInt(parseNumber()->value);
+    } else if(check(TokenType::NIL)) {
+        bump();
+        return ValueNode::ofNull();
+    } else if(check(TokenType::IDENTIFIER)) {
+        return ValueNode::ofIdentifier(parseIdentifier()->value);
+    } else {
+        return unexpected();
+    }
+}
+
diff --git a/comdel/parser/comdelparser.h b/comdel/parser/comdelparser.h
index 898219f..25f4d3f 100644
--- a/comdel/parser/comdelparser.h
+++ b/comdel/parser/comdelparser.h
@@ -69,6 +69,7 @@ private:
     PResult<PropertyNode> parseProperty(std::optional<TokenType> valueType);
     PResult<EnumerationNode> parseEnumeration();
 
+    PResult<ValueNode> parseConnectionWire();
     PResult<ComponentNode> parseComponent();
     PResult<AddressSpaceNode> parseAddress();
     PResult<PinNode> parsePin();
@@ -84,6 +85,7 @@ private:
     PResult<IfStatementNode> parseIfStatement();
     PResult<ValueNode> parseValue();
 
+
     PResult<WireInstanceNode> parseWireInstance();
     PResult<CountNode> parsePosition();
     PResult<InstanceNode> parseInstance();
diff --git a/comdel/parser/token.h b/comdel/parser/token.h
index 9b8f952..03023e7 100644
--- a/comdel/parser/token.h
+++ b/comdel/parser/token.h
@@ -65,6 +65,9 @@ enum class TokenType {
     TRUE,
     FALSE,
 
+    // NULL
+    NIL,
+
     // KEYWORDS
     KW_NAME,
     KW_INFO,
diff --git a/comdel/parser/tokenstype.cpp b/comdel/parser/tokenstype.cpp
index 524b512..458b4eb 100644
--- a/comdel/parser/tokenstype.cpp
+++ b/comdel/parser/tokenstype.cpp
@@ -76,6 +76,7 @@ TokenTables::TokenTables() {
     add( TokenType::ELSE, "else", TOKENIZABLE),
 
     add( TokenType::DEFAULT, "default", TOKENIZABLE),
+    add( TokenType::NIL, "null", TOKENIZABLE),
 
     // all keywords
     add( TokenType::KW_NAME, "@name", TOKENIZABLE),
diff --git a/mainwindow.cpp b/mainwindow.cpp
index c556403..1c75f7f 100644
--- a/mainwindow.cpp
+++ b/mainwindow.cpp
@@ -63,14 +63,14 @@ void MainWindow::onTestModal() {
             library = generator.loadLibrary(*schemaNode->library);
 
             for (auto& error : generator.getErrors()) {
-                parseContext.formatError(error, std::cout, "ERROR: ");
+                parseContext.formatError(error, std::cout, "GENERATOR ERROR: ");
             }
 
             if(library) {
                 schema = generator.loadSchema(*schemaNode, *library);
 
                 for (auto& error : generator.getErrors()) {
-                    parseContext.formatError(error, std::cout, "ERROR: ");
+                    parseContext.formatError(error, std::cout, "LIBRARY ERROR: ");
                 }
             }