From d1e19d31717cea5c2c2f891176596f9dbeb4549a Mon Sep 17 00:00:00 2001
From: Paul Beckingham <paul@beckingham.net>
Date: Tue, 22 Dec 2015 09:43:04 -0500
Subject: [PATCH] Grammar: Validates the presence of a start rule

---
 src/Grammar.cpp | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/Grammar.cpp b/src/Grammar.cpp
index bd577ee6..f6a0d192 100644
--- a/src/Grammar.cpp
+++ b/src/Grammar.cpp
@@ -172,6 +172,9 @@ std::string Grammar::dump () const
 ////////////////////////////////////////////////////////////////////////////////
 void Grammar::validate () const
 {
+  if (_start == "")
+    throw std::string ("There are no rules defined.");
+
   std::vector <std::string> allRules;
   std::vector <std::string> allTokens;
   std::vector <std::string> allLeftRecursive;