Also look at variables referenced in expressions when determining dependencies between variables

app/Engine/Cfnpp/Compiler.php

@@ -235,12 +235,18 @@ class Compiler implements \App\Engine\ICompile
 				$stack = array_merge($stack, $node->getChildren());
 			}
 
-			// We're really only handling one case here right now
 			if ($node instanceof NodeFunctionValue &&
 				$node->getName() == 'var')
 			{
 				$variables[] = $node->getValue();
 			}
+			elseif ($node instanceof NodeFunctionValue &&
+				$node->getName() == 'expr')
+			{
+				$parser = new \App\Engine\Cfnpp\Expression\Parser();
+				$expression = $parser->parse($node->getValue());
+				$variables = array_merge($variables, $expression->getReferencedVariables());
+			}
 		}
 
 		return $variables;