Convert all writers to use PandocMonad.

Since PandocMonad is an instance of MonadError, this will allow us, in a
future commit, to change all invocations of `error` to `throwError`,
which will be preferable for the pure versions. At the moment, we're
disabling the lua custom writers (this is temporary).

This requires changing the type of the Writer in Text.Pandoc. Right now,
we run `runIOorExplode` in pandoc.hs, to make the conversion easier. We
can switch it to the safer `runIO` in the future.

Note that this required a change to Text.Pandoc.PDF as well. Since
running an external program is necessarily IO, we can be clearer about
using PandocIO.

1 files changed, 26 insertions, 24 deletions

diff --git a/src/Text/Pandoc/Writers/OPML.hs b/src/Text/Pandoc/Writers/OPML.hs
index 20c2c5cbc..ce415264d 100644
--- a/src/Text/Pandoc/Writers/OPML.hs
+++ b/src/Text/Pandoc/Writers/OPML.hs
@@ -40,29 +40,30 @@ import Text.Pandoc.Writers.Markdown (writeMarkdown)
 import Text.Pandoc.Pretty
 import Text.Pandoc.Compat.Time
 import qualified Text.Pandoc.Builder as B
+import Text.Pandoc.Class (PandocMonad)
 
 -- | Convert Pandoc document to string in OPML format.
-writeOPML :: WriterOptions -> Pandoc -> String
-writeOPML opts (Pandoc meta blocks) =
+writeOPML :: PandocMonad m => WriterOptions -> Pandoc -> m String
+writeOPML opts (Pandoc meta blocks) = do
   let elements = hierarchicalize blocks
       colwidth = if writerWrapText opts == WrapAuto
                     then Just $ writerColumns opts
                     else Nothing
       meta' = B.setMeta "date" (B.str $ convertDate $ docDate meta) meta
-      Just metadata = metaToJSON opts
-                      (Just . writeMarkdown def . Pandoc nullMeta)
-                      (Just . trimr . writeMarkdown def . Pandoc nullMeta .
-                         (\ils -> [Plain ils]))
-                      meta'
-      main     = render colwidth $ vcat (map (elementToOPML opts) elements)
-      context = defField "body" main metadata
-  in  case writerTemplate opts of
-           Nothing  -> main
-           Just tpl -> renderTemplate' tpl context
+  metadata <- metaToJSON opts
+              (writeMarkdown def . Pandoc nullMeta)
+              (\ils -> trimr <$> (writeMarkdown def $ Pandoc nullMeta [Plain ils]))
+              meta'
+  main <- (render colwidth . vcat) <$> (mapM (elementToOPML opts) elements)
+  let context = defField "body" main metadata
+  return $ case writerTemplate opts of
+             Nothing  -> main
+             Just tpl -> renderTemplate' tpl context
 
-writeHtmlInlines :: [Inline] -> String
-writeHtmlInlines ils = trim $ writeHtmlString def
-                            $ Pandoc nullMeta [Plain ils]
+
+writeHtmlInlines :: PandocMonad m => [Inline] -> m String
+writeHtmlInlines ils =
+  trim <$> (writeHtmlString def $ Pandoc nullMeta [Plain ils])
 
 -- date format: RFC 822: Thu, 14 Jul 2005 23:41:05 GMT
 showDateTimeRFC822 :: UTCTime -> String
@@ -78,17 +79,18 @@ convertDate ils = maybe "" showDateTimeRFC822 $
   defaultTimeLocale "%F" =<< (normalizeDate $ stringify ils)
 
 -- | Convert an Element to OPML.
-elementToOPML :: WriterOptions -> Element -> Doc
-elementToOPML _ (Blk _) = empty
-elementToOPML opts (Sec _ _num _ title elements) =
+elementToOPML :: PandocMonad m => WriterOptions -> Element -> m Doc
+elementToOPML _ (Blk _) = return empty
+elementToOPML opts (Sec _ _num _ title elements) = do
   let isBlk (Blk _) = True
       isBlk _     = False
       fromBlk (Blk x) = x
       fromBlk _ = error "fromBlk called on non-block"
       (blocks, rest) = span isBlk elements
-      attrs = [("text", writeHtmlInlines title)] ++
-              [("_note", writeMarkdown def (Pandoc nullMeta
-                              (map fromBlk blocks)))
-                | not (null blocks)]
-  in  inTags True "outline" attrs $
-      vcat (map (elementToOPML opts) rest)
+  htmlIls <- writeHtmlInlines title
+  md <- if null blocks
+        then return []
+        else writeMarkdown def $ Pandoc nullMeta $ map fromBlk blocks
+  let attrs = [("text", htmlIls)] ++ [("_note", md)]
+  o <- mapM (elementToOPML opts) rest
+  return $ inTags True "outline" attrs $ vcat o