the EOF error changed to more informative lexer error msg

src/GF/Source/LexGF.hs

@@ -121,7 +121,7 @@ tokens str = go (alexStartPos, '\n', str)
       go inp@(pos, _, str) =
     	  case alexScan inp 0 of
     	    AlexEOF                -> []
-    	    AlexError (pos, _, _)  -> fail $ show pos ++ ": lexical error"
+    	    AlexError (pos, _, _)  -> [Err pos]
     	    AlexSkip  inp' len     -> go inp'
     	    AlexToken inp' len act -> act pos (take len str) : (go inp')
 

src/GF/Source/ParGF.hs

@@ -3133,7 +3133,11 @@ thenM = (>>=)
 
 happyError :: [Token] -> Err a
 happyError ts =
-  Bad $ "syntax error at " ++ tokenPos ts ++ if null ts then [] else (" before " ++ unwords (map prToken (take 4 ts)))
+  Bad $ "syntax error at " ++ tokenPos ts ++ 
+  case ts of
+    [] -> []
+    [Err _] -> " due to lexer error" 
+    _ -> (" before " ++ unwords (map prToken (take 4 ts)))
 
 myLexer = tokens
 {-# LINE 1 "GenericTemplate.hs" #-}