Variable fixes (#67)

* Reproduce if throws UnknownOperatorException

* Fix variable detection

* Adding IncorrectNumberOfFunctionParametersException

* Removing tabs

* Better exception message text

1 files changed, 1 insertions, 1 deletions

diff --git a/src/NXP/Classes/Calculator.php b/src/NXP/Classes/Calculator.php
index 94c6933..bcb4b4e 100644
--- a/src/NXP/Classes/Calculator.php
+++ b/src/NXP/Classes/Calculator.php
@@ -77,7 +77,7 @@ class Calculator
         }
         $result = array_pop($stack);
         if ($result === null || !empty($stack)) {
-            throw new IncorrectExpressionException();
+            throw new IncorrectExpressionException('Stack must be empty');
         }
         return $result->value;
     }