Use throwError instead of fail when appropriate.

src/Text/Pandoc/Readers/Markdown.hs

@@ -258,10 +258,11 @@ yamlBsToMeta bstr = do
                                  err' pos
                     return . return $ mempty
 
-nodeToKey :: Monad m => YAML.Node YE.Pos -> m Text
+nodeToKey :: PandocMonad m => YAML.Node YE.Pos -> m Text
 nodeToKey (YAML.Scalar _ (YAML.SStr t))       = return t
 nodeToKey (YAML.Scalar _ (YAML.SUnknown _ t)) = return t
-nodeToKey _                                 = Prelude.fail "Non-string key in YAML mapping"
+nodeToKey _  = throwError $ PandocParseError
+                              "Non-string key in YAML mapping"
 
 toMetaValue :: PandocMonad m
             => Text -> MarkdownParser m (F MetaValue)

src/Text/Pandoc/Writers/Muse.hs

@@ -26,6 +26,7 @@ even though it is supported only in Emacs Muse.
 -}
 module Text.Pandoc.Writers.Muse (writeMuse) where
 import Prelude
+import Control.Monad.Except (throwError)
 import Control.Monad.Reader
 import Control.Monad.State.Strict
 import Data.Char (isAlphaNum, isAsciiLower, isAsciiUpper, isDigit, isSpace)
@@ -37,6 +38,7 @@ import Data.Text (Text)
 import System.FilePath (takeExtension)
 import Text.Pandoc.Class (PandocMonad)
 import Text.Pandoc.Definition
+import Text.Pandoc.Error
 import Text.Pandoc.ImageSize
 import Text.Pandoc.Options
 import Text.DocLayout
@@ -607,7 +609,8 @@ inlineToMuse (Subscript lst) = do
   modify $ \st -> st { stUseTags = False }
   return $ "<sub>" <> contents <> "</sub>"
 inlineToMuse SmallCaps {} =
-  Prelude.fail "SmallCaps should be expanded before normalization"
+  throwError $ PandocShouldNeverHappenError
+    "SmallCaps should be expanded before normalization"
 inlineToMuse (Quoted SingleQuote lst) = do
   contents <- inlineListToMuse lst
   modify $ \st -> st { stUseTags = False }

src/Text/Pandoc/Writers/OOXML.hs

@@ -25,6 +25,8 @@ module Text.Pandoc.Writers.OOXML ( mknode
 import Prelude
 import Codec.Archive.Zip
 import Control.Monad.Reader
+import Control.Monad.Except (throwError)
+import Text.Pandoc.Error
 import qualified Data.ByteString as B
 import qualified Data.ByteString.Lazy as BL
 import qualified Data.ByteString.Lazy.Char8 as BL8
@@ -50,13 +52,15 @@ renderXml :: Element -> BL.ByteString
 renderXml elt = BL8.pack "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n" <>
   UTF8.fromStringLazy (showElement elt)
 
-parseXml :: (PandocMonad m) => Archive -> Archive -> String -> m Element
+parseXml :: PandocMonad m => Archive -> Archive -> String -> m Element
 parseXml refArchive distArchive relpath =
   case findEntryByPath relpath refArchive `mplus`
          findEntryByPath relpath distArchive of
-            Nothing -> Prelude.fail $ relpath ++ " missing in reference file"
+            Nothing -> throwError $ PandocSomeError $
+                        relpath ++ " missing in reference file"
             Just e  -> case parseXMLDoc . UTF8.toStringLazy . fromEntry $ e of
-                       Nothing -> Prelude.fail $ relpath ++ " corrupt in reference file"
+                       Nothing -> throwError $ PandocSomeError $
+                                   relpath ++ " corrupt in reference file"
                        Just d  -> return d
 
 -- Copied from Util