diff --git a/example/math_expression/main.go b/example/math_expression/main.go
index 35f7c3b..bfece39 100644
--- a/example/math_expression/main.go
+++ b/example/math_expression/main.go
@@ -1,3 +1,5 @@
+// +build example
+
 package main
 
 import (
@@ -6,16 +8,6 @@ import (
 	"github.com/neonxp/unilex"
 )
 
-var output []unilex.Lexem = []unilex.Lexem{}
-var opPriority = map[string]int{
-	"^": 3,
-	"!": 3,
-	"*": 2,
-	"/": 2,
-	"+": 1,
-	"-": 1,
-}
-
 func main() {
 
 	l := unilex.New("10 * (20.0 + 30.0)")
diff --git a/example/math_expression/rpn.go b/example/math_expression/rpn.go
index b65983d..84de59c 100644
--- a/example/math_expression/rpn.go
+++ b/example/math_expression/rpn.go
@@ -1,3 +1,5 @@
+// +build example
+
 package main
 
 // Helper functions to convert infix notation to RPN and calculates expression result.
@@ -10,6 +12,15 @@ import (
 	"github.com/neonxp/unilex"
 )
 
+var opPriority = map[string]int{
+	"^": 3,
+	"!": 3,
+	"*": 2,
+	"/": 2,
+	"+": 1,
+	"-": 1,
+}
+
 func infixToRPNotation(l *unilex.Lexer) []unilex.Lexem {
 	output := []unilex.Lexem{}
 	stack := lexemStack{}
diff --git a/example/math_expression/stack.go b/example/math_expression/stack.go
index 2ca8acc..b6c37b9 100644
--- a/example/math_expression/stack.go
+++ b/example/math_expression/stack.go
@@ -1,3 +1,5 @@
+// +build example
+
 package main
 
 // Simple lexem stack implementation.