From e816b86a3e30ae02757e1e55078bdfc0724bd6d0 Mon Sep 17 00:00:00 2001
From: Danila Fedorin <danila.fedorin@gmail.com>
Date: Wed, 26 Jul 2017 13:24:46 -0700
Subject: [PATCH] Correctly handle un-matched tokens and end-of-string
 situations.

---
 src/org/nwapw/abacus/lexing/Lexer.java | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/org/nwapw/abacus/lexing/Lexer.java b/src/org/nwapw/abacus/lexing/Lexer.java
index 2813061..1a3cab8 100644
--- a/src/org/nwapw/abacus/lexing/Lexer.java
+++ b/src/org/nwapw/abacus/lexing/Lexer.java
@@ -87,11 +87,12 @@ public class Lexer<T> {
         int index = startAt;
         ArrayList<Match<T>> matches = new ArrayList<>();
         Match<T> lastMatch = null;
-        while((lastMatch = lexOne(from, index, compare)) != null && index < from.length()){
+        while(index < from.length() && (lastMatch = lexOne(from, index, compare)) != null){
             if(lastMatch.getTo() == lastMatch.getFrom()) return null;
             matches.add(lastMatch);
             index += lastMatch.getTo() - lastMatch.getFrom();
         }
+        if(lastMatch == null) return null;
         return matches;
     }