diff --git a/src/NXP/Classes/Calculator.php b/src/NXP/Classes/Calculator.php
index 62dbc17..980a52b 100644
--- a/src/NXP/Classes/Calculator.php
+++ b/src/NXP/Classes/Calculator.php
@@ -36,21 +36,17 @@ class Calculator
     {
         $stack = [];
         foreach ($tokens as $token) {
-            if ($token instanceof TokenNumber) {
-                array_push($stack, $token);
-            } else if ($token instanceof TokenStringDoubleQuoted) {
-                array_push($stack, $token);
-            } else if ($token instanceof TokenStringSingleQuoted) {
-                array_push($stack, $token);
+            if ($token instanceof TokenNumber || $token instanceof TokenStringDoubleQuoted || $token instanceof TokenStringSingleQuoted) {
+                $stack[] = $token;
             } else if ($token instanceof TokenVariable) {
                 $variable = $token->getValue();
                 if (!array_key_exists($variable, $variables)) {
                     throw new UnknownVariableException($variable);
                 }
                 $value = $variables[$variable];
-                array_push($stack, new TokenNumber($value));
+                $stack[] = new TokenNumber($value);
             } else if ($token instanceof InterfaceOperator || $token instanceof TokenFunction) {
-                array_push($stack, $token->execute($stack));
+                $stack[] = $token->execute($stack);
             }
         }
         $result = array_pop($stack);
diff --git a/src/NXP/Classes/Lexer.php b/src/NXP/Classes/Lexer.php
index a511c9b..898d8c1 100644
--- a/src/NXP/Classes/Lexer.php
+++ b/src/NXP/Classes/Lexer.php
@@ -77,7 +77,7 @@ class Lexer
             } elseif ($token instanceof TokenVariable) {
                 $output[] = $token;
             } elseif ($token instanceof TokenFunction) {
-                array_push($stack, $token);
+                $stack[] = $token;
             } elseif ($token instanceof AbstractOperator) {
                 // While we have something on the stack
                 while (($count = count($stack)) > 0
@@ -104,9 +104,12 @@ class Lexer
                     $output[] = array_pop($stack);
                 }
 
-                array_push($stack, $token);
+                // Comma operators do nothing really, don't put them on the stack
+                if (! ($token instanceof TokenComma)) {
+                  $stack[] = $token;
+                }
             } elseif ($token instanceof TokenLeftBracket) {
-                array_push($stack, $token);
+                $stack[] = $token;
             } elseif ($token instanceof TokenRightBracket) {
                 while (($current = array_pop($stack)) && (!($current instanceof TokenLeftBracket))) {
                     $output[] = $current;
diff --git a/src/NXP/Classes/Token/TokenComma.php b/src/NXP/Classes/Token/TokenComma.php
index 6a45595..9d997e1 100644
--- a/src/NXP/Classes/Token/TokenComma.php
+++ b/src/NXP/Classes/Token/TokenComma.php
@@ -13,7 +13,7 @@ namespace NXP\Classes\Token;
 /**
  * @author Alexander Kiryukhin <a.kiryukhin@mail.ru>
  */
-class TokenComma implements InterfaceToken
+class TokenComma extends AbstractOperator
 {
     /**
      * @return string
@@ -22,4 +22,32 @@ class TokenComma implements InterfaceToken
     {
         return '\,';
     }
+
+    /**
+     * Comma operator is lowest priority
+     *
+     * @return int
+     */
+    public function getPriority()
+    {
+        return 0;
+    }
+
+    /**
+     * @return string
+     */
+    public function getAssociation()
+    {
+        return self::RIGHT_RIGHT;
+    }
+
+    /**
+     * @param  array       $stack
+     * @return TokenNumber
+     */
+    public function execute(&$stack)
+    {
+        // Comma operators don't do anything, stack has already executed
+    }
+
 }
diff --git a/src/NXP/Classes/Token/TokenFunction.php b/src/NXP/Classes/Token/TokenFunction.php
index 04eae30..432f107 100644
--- a/src/NXP/Classes/Token/TokenFunction.php
+++ b/src/NXP/Classes/Token/TokenFunction.php
@@ -32,9 +32,10 @@ class TokenFunction extends AbstractContainerToken implements InterfaceFunction
         $args = [];
         list($places, $function) = $this->value;
         for ($i = 0; $i < $places; $i++) {
-            $args[] = array_pop($stack)->getValue();
+            array_unshift($args, array_pop($stack)->getValue());
         }
-        $result = call_user_func_array($function, array_reverse($args));
+
+        $result = call_user_func_array($function, $args);
 
         return new TokenNumber($result);
     }
diff --git a/tests/MathTest.php b/tests/MathTest.php
index 81f0230..5bb2ec0 100644
--- a/tests/MathTest.php
+++ b/tests/MathTest.php
@@ -135,17 +135,17 @@ class MathTest extends \PHPUnit_Framework_TestCase
     }
 
     public function testFunctionParameterOrder()
-		{
-				$calculator = new MathExecutor();
+    {
+        $calculator = new MathExecutor();
 
-				$calculator->addFunction('concat', function ($arg1, $arg2)
-						{
-						return $arg1.$arg2;
-						}
-				);
-				$this->assertEquals('testing', $calculator->execute('concat("test","ing")'));
-				$this->assertEquals('testing', $calculator->execute("concat('test','ing')"));
-		}
+        $calculator->addFunction('concat', function ($arg1, $arg2)
+            {
+            return $arg1.$arg2;
+            }
+        );
+        $this->assertEquals('testing', $calculator->execute('concat("test","ing")'));
+        $this->assertEquals('testing', $calculator->execute("concat('test','ing')"));
+    }
 
     public function testFunction()
     {
@@ -154,17 +154,33 @@ class MathTest extends \PHPUnit_Framework_TestCase
         $this->assertEquals(round(100/30), $calculator->execute('round(100/30)'));
     }
 
+    public function testEvaluateFunctionParameters()
+    {
+        $calculator = new MathExecutor();
+        $calculator->addFunction('round', function ($value, $decimals)
+          {
+            return round($value, $decimals);
+          }
+        );
+        $expression = 'round(100 * 1.111111, 2)';
+        eval('$phpResult = ' . $expression . ';');
+        $this->assertEquals($phpResult, $calculator->execute($expression));
+        $expression = 'round((100*0.04)+(((100*1.02)+0.5)*1.28),2)';
+        eval('$phpResult = ' . $expression . ';');
+        $this->assertEquals($phpResult, $calculator->execute($expression));
+    }
+
     public function testQuotes()
     {
         $calculator = new MathExecutor();
         $testString = "some, long. arg; with: different-separators!";
         $calculator->addFunction('test', function ($arg) use ($testString)
-						{
-						$this->assertEquals($testString, $arg);
+            {
+            $this->assertEquals($testString, $arg);
             return 0;
-						}
-				);
+            }
+        );
         $calculator->execute('test("' . $testString . '")'); // single quotes
         $calculator->execute("test('" . $testString . "')"); // double quotes
     }
-}
\ No newline at end of file
+}