improvements to lexical error reporting

[ghc-hetmet.git] / compiler / parser / Lexer.x

diff --git a/compiler/parser/Lexer.x b/compiler/parser/Lexer.x
index 1ede5f6..f6863c6 100644 (file)
--- a/compiler/parser/Lexer.x
+++ b/compiler/parser/Lexer.x
@@ -1210,6 +1210,7 @@ alexGetChar :: AlexInput -> Maybe (Char,AlexInput)
 alexGetChar (AI loc ofs s) 
   | atEnd s   = Nothing
   | otherwise = adj_c `seq` loc' `seq` ofs' `seq` s' `seq` 
+               --trace (show (ord c)) $
                Just (adj_c, (AI loc' ofs' s'))
   where (c,s') = nextChar s
         loc'   = advanceSrcLoc loc c
@@ -1259,6 +1260,7 @@ alexGetChar' :: AlexInput -> Maybe (Char,AlexInput)
 alexGetChar' (AI loc ofs s) 
   | atEnd s   = Nothing
   | otherwise = c `seq` loc' `seq` ofs' `seq` s' `seq` 
+               --trace (show (ord c)) $
                Just (c, (AI loc' ofs' s'))
   where (c,s') = nextChar s
         loc'   = advanceSrcLoc loc c
@@ -1443,15 +1445,13 @@ lexToken = do
        span `seq` setLastToken span bytes
        t span buf bytes
 
--- ToDo: Alex reports the buffer at the start of the erroneous lexeme,
--- but it would be more informative to report the location where the
--- error was actually discovered, especially if this is a decoding
--- error.
-reportLexError loc1 loc2 buf str = 
+reportLexError loc1 loc2 buf str
+  | atEnd buf = failLocMsgP loc1 loc2 (str ++ " at end of input")
+  | otherwise =
   let 
        c = fst (nextChar buf)
   in
   if c == '\0' -- decoding errors are mapped to '\0', see utf8DecodeChar#
-    then failLocMsgP loc2 loc2 "UTF-8 decoding error"
+    then failLocMsgP loc2 loc2 (str ++ " (UTF-8 decoding error)")
     else failLocMsgP loc1 loc2 (str ++ " at character " ++ show c)
 }