Haddock reader: improved error reporting.

3 files changed, 9 insertions, 6 deletions

diff --git a/src/Text/Pandoc/Readers/Haddock.hs b/src/Text/Pandoc/Readers/Haddock.hs
index 49154b0ca..081ec7b5e 100644
--- a/src/Text/Pandoc/Readers/Haddock.hs
+++ b/src/Text/Pandoc/Readers/Haddock.hs
@@ -24,8 +24,10 @@ readHaddock :: ReaderOptions -- ^ Reader options
 readHaddock _ s = Pandoc (Meta [] [] []) blocks
   where
     blocks = case parseParas (tokenise s (0,0)) of
-        Nothing -> []
-        Just x -> mergeLists (toList x)
+        Left [] -> error "parse failure"
+        Left (tok:_) -> error $ "parse failure " ++ pos (tokenPos tok)
+          where pos (l, c) = "(line " ++ show l ++ ", column " ++ show c ++ ")"
+        Right x -> mergeLists (toList x)
 
 -- similar to 'docAppend' in Haddock.Doc
 mergeLists :: [Block] -> [Block]
diff --git a/src/Text/Pandoc/Readers/Haddock/Lex.x b/src/Text/Pandoc/Readers/Haddock/Lex.x
index 902ac84c0..9d686c885 100644
--- a/src/Text/Pandoc/Readers/Haddock/Lex.x
+++ b/src/Text/Pandoc/Readers/Haddock/Lex.x
@@ -19,7 +19,8 @@
 module Text.Pandoc.Readers.Haddock.Lex (
     Token(..),
     LToken,
-    tokenise
+    tokenise,
+    tokenPos
  ) where
 
 import Data.Char
diff --git a/src/Text/Pandoc/Readers/Haddock/Parse.y b/src/Text/Pandoc/Readers/Haddock/Parse.y
index 26d7c287d..c45e09113 100644
--- a/src/Text/Pandoc/Readers/Haddock/Parse.y
+++ b/src/Text/Pandoc/Readers/Haddock/Parse.y
@@ -46,7 +46,7 @@ import Data.Sequence (viewr, ViewR(..))
     PARA    { (TokPara,_) }
     STRING  { (TokString $$,_) }
 
-%monad { Maybe }
+%monad { Either [LToken] }
 
 %name parseParas doc
 %name parseString seq
@@ -126,8 +126,8 @@ strings :: { String }
     | STRING strings    { $1 ++ $2 }
 
 {
-happyError :: [LToken] -> Maybe a
-happyError toks = Nothing
+happyError :: [LToken] -> Either [LToken] a
+happyError toks = Left toks
 
 para' :: Inlines -> Blocks
 para' (Many ils) =