diff --git a/internal/parser/ast.go b/internal/parser/ast.go
index 78ffb07..afe6bc6 100644
--- a/internal/parser/ast.go
+++ b/internal/parser/ast.go
@@ -153,3 +153,12 @@ type BinaryExpression struct {
 
 func (b *BinaryExpression) Pos() Position { return b.Position }
 func (b *BinaryExpression) isValue()      {}
+
+type UnaryExpression struct {
+	Position Position
+	Operator Token
+	Right    Value
+}
+
+func (u *UnaryExpression) Pos() Position { return u.Position }
+func (u *UnaryExpression) isValue()      {}
diff --git a/internal/parser/lexer.go b/internal/parser/lexer.go
index 2bbead7..cbfcfa7 100644
--- a/internal/parser/lexer.go
+++ b/internal/parser/lexer.go
@@ -147,18 +147,12 @@ func (l *Lexer) NextToken() Token {
 		case ']':
 			return l.emit(TokenRBracket)
 		case '+':
-			if unicode.IsSpace(l.peek()) {
+			if unicode.IsSpace(l.peek()) || unicode.IsDigit(l.peek()) {
 				return l.emit(TokenPlus)
 			}
 			return l.lexObjectIdentifier()
 		case '-':
-			if unicode.IsDigit(l.peek()) {
-				return l.lexNumber()
-			}
-			if unicode.IsSpace(l.peek()) {
-				return l.emit(TokenMinus)
-			}
-			return l.lexIdentifier()
+			return l.emit(TokenMinus)
 		case '*':
 			return l.emit(TokenStar)
 		case '/':
@@ -242,13 +236,28 @@ func (l *Lexer) lexString() Token {
 }
 
 func (l *Lexer) lexNumber() Token {
-	for {
-		r := l.next()
-		if unicode.IsDigit(r) || unicode.IsLetter(r) || r == '.' || r == '-' || r == '+' {
-			continue
+	// Consume initial digits (already started)
+	l.lexDigits()
+
+	if l.peek() == '.' {
+		l.next()
+		l.lexDigits()
+	}
+
+	if r := l.peek(); r == 'e' || r == 'E' {
+		l.next()
+		if p := l.peek(); p == '+' || p == '-' {
+			l.next()
 		}
-		l.backup()
-		return l.emit(TokenNumber)
+		l.lexDigits()
+	}
+
+	return l.emit(TokenNumber)
+}
+
+func (l *Lexer) lexDigits() {
+	for unicode.IsDigit(l.peek()) {
+		l.next()
 	}
 }
 
@@ -318,7 +327,7 @@ func (l *Lexer) lexHashIdentifier() Token {
 func (l *Lexer) lexVariableReference() Token {
 	for {
 		r := l.next()
-		if unicode.IsLetter(r) || unicode.IsDigit(r) || r == '_' || r == '-' {
+		if unicode.IsLetter(r) || unicode.IsDigit(r) || r == '_' {
 			continue
 		}
 		l.backup()
diff --git a/internal/parser/parser.go b/internal/parser/parser.go
index 6d1f73b..6bcee1f 100644
--- a/internal/parser/parser.go
+++ b/internal/parser/parser.go
@@ -299,8 +299,27 @@ func (p *Parser) parseAtom() (Value, bool) {
 		return &ReferenceValue{Position: tok.Position, Value: tok.Value}, true
 	case TokenVariableReference:
 		return &VariableReferenceValue{Position: tok.Position, Name: tok.Value}, true
+	case TokenMinus:
+		val, ok := p.parseAtom()
+		if !ok {
+			return nil, false
+		}
+		return &UnaryExpression{Position: tok.Position, Operator: tok, Right: val}, true
 	case TokenObjectIdentifier:
 		return &VariableReferenceValue{Position: tok.Position, Name: tok.Value}, true
+	case TokenSymbol:
+		if tok.Value == "(" {
+			val, ok := p.parseExpression(0)
+			if !ok {
+				return nil, false
+			}
+			if next := p.next(); next.Type != TokenSymbol || next.Value != ")" {
+				p.addError(next.Position, "expected )")
+				return nil, false
+			}
+			return val, true
+		}
+		fallthrough
 	case TokenLBrace:
 		arr := &ArrayValue{Position: tok.Position}
 		for {
diff --git a/internal/validator/validator.go b/internal/validator/validator.go
index 4e3f74e..7be86ff 100644
--- a/internal/validator/validator.go
+++ b/internal/validator/validator.go
@@ -236,6 +236,108 @@ func (v *Validator) valueToInterface(val parser.Value, ctx *index.ProjectNode) i
 			arr = append(arr, v.valueToInterface(e, ctx))
 		}
 		return arr
+	case *parser.BinaryExpression:
+		left := v.valueToInterface(t.Left, ctx)
+		right := v.valueToInterface(t.Right, ctx)
+		return v.evaluateBinary(left, t.Operator.Type, right)
+	case *parser.UnaryExpression:
+		val := v.valueToInterface(t.Right, ctx)
+		return v.evaluateUnary(t.Operator.Type, val)
+	}
+	return nil
+}
+
+func (v *Validator) evaluateBinary(left interface{}, op parser.TokenType, right interface{}) interface{} {
+	if left == nil || right == nil {
+		return nil
+	}
+
+	if op == parser.TokenConcat {
+		return fmt.Sprintf("%v%v", left, right)
+	}
+
+	toInt := func(val interface{}) (int64, bool) {
+		switch v := val.(type) {
+		case int64:
+			return v, true
+		case int:
+			return int64(v), true
+		}
+		return 0, false
+	}
+
+	toFloat := func(val interface{}) (float64, bool) {
+		switch v := val.(type) {
+		case float64:
+			return v, true
+		case int64:
+			return float64(v), true
+		case int:
+			return float64(v), true
+		}
+		return 0, false
+	}
+
+	if l, ok := toInt(left); ok {
+		if r, ok := toInt(right); ok {
+			switch op {
+			case parser.TokenPlus:
+				return l + r
+			case parser.TokenMinus:
+				return l - r
+			case parser.TokenStar:
+				return l * r
+			case parser.TokenSlash:
+				if r != 0 {
+					return l / r
+				}
+			case parser.TokenPercent:
+				if r != 0 {
+					return l % r
+				}
+			}
+		}
+	}
+
+	if l, ok := toFloat(left); ok {
+		if r, ok := toFloat(right); ok {
+			switch op {
+			case parser.TokenPlus:
+				return l + r
+			case parser.TokenMinus:
+				return l - r
+			case parser.TokenStar:
+				return l * r
+			case parser.TokenSlash:
+				if r != 0 {
+					return l / r
+				}
+			}
+		}
+	}
+
+	return nil
+}
+
+func (v *Validator) evaluateUnary(op parser.TokenType, val interface{}) interface{} {
+	if val == nil {
+		return nil
+	}
+
+	switch op {
+	case parser.TokenMinus:
+		switch v := val.(type) {
+		case int64:
+			return -v
+		case float64:
+			return -v
+		}
+	case parser.TokenSymbol: // ! is Symbol?
+		// Parser uses TokenSymbol for ! ?
+		// Lexer: '!' -> Symbol.
+		if b, ok := val.(bool); ok {
+			return !b
+		}
 	}
 	return nil
 }
diff --git a/test/expression_parsing_test.go b/test/expression_parsing_test.go
new file mode 100644
index 0000000..1643141
--- /dev/null
+++ b/test/expression_parsing_test.go
@@ -0,0 +1,60 @@
+package integration
+
+import (
+	"os"
+	"strings"
+	"testing"
+
+	"github.com/marte-community/marte-dev-tools/internal/builder"
+)
+
+func TestExpressionParsing(t *testing.T) {
+	content := `
+#var A: int = 10
+#var B: int = 2
+
++Obj = {
+    // 1. Multiple variables
+    Expr1 = @A + @B + @A
+    
+    // 2. Brackets
+    Expr2 = (@A + 2) * @B
+    
+    // 3. No space operator (variable name strictness)
+    Expr3 = @A-2
+}
+`
+	f, _ := os.CreateTemp("", "expr_test.marte")
+	f.WriteString(content)
+	f.Close()
+	defer os.Remove(f.Name())
+
+	b := builder.NewBuilder([]string{f.Name()}, nil)
+
+	outF, _ := os.CreateTemp("", "out.marte")
+	defer os.Remove(outF.Name())
+	
+	err := b.Build(outF)
+	if err != nil {
+		t.Fatalf("Build failed: %v", err)
+	}
+	outF.Close()
+
+	outContent, _ := os.ReadFile(outF.Name())
+	outStr := string(outContent)
+
+	// Expr1: 10 + 2 + 10 = 22
+	if !strings.Contains(outStr, "Expr1 = 22") {
+		t.Errorf("Expr1 failed. Got:\n%s", outStr)
+	}
+	
+	// Expr2: (10 + 2) * 2 = 24
+	if !strings.Contains(outStr, "Expr2 = 24") {
+		t.Errorf("Expr2 failed. Got:\n%s", outStr)
+	}
+	
+	// Expr3: 10 - 2 = 8
+	if !strings.Contains(outStr, "Expr3 = 8") {
+		t.Errorf("Expr3 failed. Got:\n%s", outStr)
+	}
+}
diff --git a/test/expression_whitespace_test.go b/test/expression_whitespace_test.go
new file mode 100644
index 0000000..a338264
--- /dev/null
+++ b/test/expression_whitespace_test.go
@@ -0,0 +1,39 @@
+package integration
+
+import (
+	"os"
+	"strings"
+	"testing"
+
+	"github.com/marte-community/marte-dev-tools/internal/builder"
+)
+
+func TestExpressionWhitespace(t *testing.T) {
+	content := `
++Obj = {
+    NoSpace = 2+2
+    WithSpace = 2 + 2
+}
+`
+	f, _ := os.CreateTemp("", "expr_ws.marte")
+	f.WriteString(content)
+	f.Close()
+	defer os.Remove(f.Name())
+
+	b := builder.NewBuilder([]string{f.Name()}, nil)
+
+	outF, _ := os.CreateTemp("", "out.marte")
+	defer os.Remove(outF.Name())
+	b.Build(outF)
+	outF.Close()
+
+	outContent, _ := os.ReadFile(outF.Name())
+	outStr := string(outContent)
+
+	if !strings.Contains(outStr, "NoSpace = 4") {
+		t.Errorf("NoSpace failed. Got:\n%s", outStr)
+	}
+	if !strings.Contains(outStr, "WithSpace = 4") {
+		t.Errorf("WithSpace failed. Got:\n%s", outStr)
+	}
+}