diff --git a/src/main/fr/celticinfo/lox/AstPrinter.kt b/src/main/fr/celticinfo/lox/AstPrinter.kt
index 203f173..99464f4 100644
--- a/src/main/fr/celticinfo/lox/AstPrinter.kt
+++ b/src/main/fr/celticinfo/lox/AstPrinter.kt
@@ -5,6 +5,10 @@ class AstPrinter : ExprVisitor<String> {
         return expr.accept(this)
     }
 
+    override fun visitCall(expr: Call): String {
+        return parenthesize("call", expr.callee, *expr.arguments.toTypedArray())
+    }
+
     override fun visitAssign(expr: Assign): String {
         return parenthesize("=", expr)
     }
diff --git a/src/main/fr/celticinfo/lox/Interpreter.kt b/src/main/fr/celticinfo/lox/Interpreter.kt
index c85efc7..0c81f1f 100644
--- a/src/main/fr/celticinfo/lox/Interpreter.kt
+++ b/src/main/fr/celticinfo/lox/Interpreter.kt
@@ -3,7 +3,24 @@ package fr.celticinfo.lox
 import fr.celticinfo.lox.TokenType.*
 
 class Interpreter: ExprVisitor<Any?>, StmtVisitor<Unit>{
-    private var environment = Environment()
+    private var globals = Environment()
+    private var environment = globals
+
+    constructor() {
+        globals.define("clock", object : LoxCallable {
+            override fun arity(): Int {
+                return 0
+            }
+
+            override fun call(interpreter: Interpreter, arguments: List<Any?>): Any? {
+                return System.currentTimeMillis().toDouble() / 1000.0
+            }
+
+            override fun toString(): String {
+                return "<native fn>"
+            }
+        })
+    }
 
     fun interpret(statements: List<Stmt?>) {
         try {
diff --git a/src/main/fr/celticinfo/loxext/RpnPrinter.kt b/src/main/fr/celticinfo/loxext/RpnPrinter.kt
index 76040c6..533b523 100644
--- a/src/main/fr/celticinfo/loxext/RpnPrinter.kt
+++ b/src/main/fr/celticinfo/loxext/RpnPrinter.kt
@@ -7,6 +7,10 @@ class RpnPrinter : ExprVisitor<String> {
         return expr.accept(this)
     }
 
+    override fun visitCall(expr: Call): String {
+        return stack("call", expr.callee, *expr.arguments.toTypedArray())
+    }
+
     override fun visitAssign(expr: Assign): String {
         return stack("=", expr)
     }
diff --git a/src/test/fr/celticinfo/lox/InterpreterTest.kt b/src/test/fr/celticinfo/lox/InterpreterTest.kt
index 2924e83..d945373 100644
--- a/src/test/fr/celticinfo/lox/InterpreterTest.kt
+++ b/src/test/fr/celticinfo/lox/InterpreterTest.kt
@@ -1,6 +1,7 @@
 package fr.celticinfo.lox
 
 import fr.celticinfo.loxext.RpnPrinter
+import org.junit.jupiter.api.Assertions
 import org.junit.jupiter.api.assertDoesNotThrow
 import java.io.ByteArrayOutputStream
 import java.io.PrintStream
@@ -358,4 +359,32 @@ for (var b = 1; a < 10000; b = temp + b) {
             System.setOut(standardOut)
         }
     }
+
+    @Test
+    fun `Clock native function should return a valid timestamp`() {
+        val standardOut = System.out
+        val outputStreamCaptor = ByteArrayOutputStream()
+
+        System.setOut(PrintStream(outputStreamCaptor))
+
+        try {
+            val code = """
+print clock();
+            """.trimIndent()
+            val scanner = Scanner(code)
+            val tokens = scanner.scanTokens()
+            val parser = Parser(tokens)
+            val statements = parser.parse()
+            Assertions.assertEquals(1, statements.size)
+
+            Interpreter().interpret(statements)
+            val output = outputStreamCaptor.toString().trim()
+            val timestamp = output.toDoubleOrNull()
+            Assertions.assertNotNull(timestamp)
+            Assertions.assertTrue(timestamp!! >= 0)
+        } finally {
+            System.setOut(standardOut)
+        }
+    }
+
 }
\ No newline at end of file