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, 148 insertions, 68 deletions

diff --git a/src/Text/Pandoc.hs b/src/Text/Pandoc.hs
index 703d0a002..5bb015fc2 100644
--- a/src/Text/Pandoc.hs
+++ b/src/Text/Pandoc.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE ScopedTypeVariables, FlexibleInstances #-}
+{-# LANGUAGE ScopedTypeVariables, FlexibleInstances, GADTs #-}
 {-
 Copyright (C) 2006-2016 John MacFarlane <jgm@berkeley.edu>
 
@@ -63,7 +63,8 @@ module Text.Pandoc
                , module Text.Pandoc.Error
                -- * Lists of readers and writers
                , readers
-               , writers
+               -- , writers
+               , writers'
                -- * Readers: converting /to/ Pandoc format
                , Reader (..)
                , mkStringReader
@@ -87,7 +88,8 @@ module Text.Pandoc
                , readTxt2TagsNoMacros
                , readEPUB
                -- * Writers: converting /from/ Pandoc format
-              , Writer (..)
+              -- , Writer (..)
+               , Writer'(..)
                , writeNative
                , writeJSON
                , writeMarkdown
@@ -122,7 +124,8 @@ module Text.Pandoc
                , module Text.Pandoc.Templates
                -- * Miscellaneous
                , getReader
-               , getWriter
+               -- , getWriter
+               , getWriter'
                , getDefaultExtensions
                , ToJsonFilter(..)
                , pandocVersion
@@ -180,7 +183,7 @@ import Text.Pandoc.Options
 import Text.Pandoc.Shared (safeRead, warn, mapLeft, pandocVersion)
 import Text.Pandoc.MediaBag (MediaBag)
 import Text.Pandoc.Error
-import Text.Pandoc.Class (runIOorExplode)
+import Text.Pandoc.Class (PandocMonad)
 import Data.Aeson
 import qualified Data.ByteString.Lazy as BL
 import Data.List (intercalate)
@@ -262,74 +265,137 @@ readers = [ ("native"       , StringReader $ \_ s -> return $ readNative s)
            ,("epub"         , mkBSReader readEPUB)
            ]
 
-data Writer = PureStringWriter   (WriterOptions -> Pandoc -> String)
-            | IOStringWriter     (WriterOptions -> Pandoc -> IO String)
-            | IOByteStringWriter (WriterOptions -> Pandoc -> IO BL.ByteString)
+-- data Writer = PureStringWriter   (WriterOptions -> Pandoc -> String)
+--             | IOStringWriter     (WriterOptions -> Pandoc -> IO String)
+--             | IOByteStringWriter (WriterOptions -> Pandoc -> IO BL.ByteString)
+
+-- -- | Association list of formats and writers.
+-- writers :: [ ( String, Writer ) ]
+-- writers = [
+--    ("native"       , PureStringWriter writeNative)
+--   ,("json"         , PureStringWriter writeJSON)
+--   ,("docx"         , IOByteStringWriter $ \o doc ->
+--                       runIOorExplode $ writeDocx o doc)
+--   ,("odt"          , IOByteStringWriter $ \o doc ->
+--                       runIOorExplode $ writeODT o doc)
+--   ,("epub"         , IOByteStringWriter $ \o doc ->
+--                       runIOorExplode $
+--                       writeEPUB o{ writerEpubVersion = Just EPUB2 } doc)
+--   ,("epub3"        , IOByteStringWriter $ \o doc ->
+--                       runIOorExplode $ 
+--                       writeEPUB o{ writerEpubVersion = Just EPUB3 } doc)
+--   ,("fb2"          , IOStringWriter $ \o doc ->
+--                       runIOorExplode $ writeFB2 o doc)
+--   ,("html"         , PureStringWriter writeHtmlString)
+--   ,("html5"        , PureStringWriter $ \o ->
+--      writeHtmlString o{ writerHtml5 = True })
+--   ,("icml"         , IOStringWriter $ \o doc ->
+--                       runIOorExplode $ writeICML o doc)
+--   ,("s5"           , PureStringWriter $ \o ->
+--      writeHtmlString o{ writerSlideVariant = S5Slides
+--                       , writerTableOfContents = False })
+--   ,("slidy"        , PureStringWriter $ \o ->
+--      writeHtmlString o{ writerSlideVariant = SlidySlides })
+--   ,("slideous"     , PureStringWriter $ \o ->
+--      writeHtmlString o{ writerSlideVariant = SlideousSlides })
+--   ,("dzslides"     , PureStringWriter $ \o ->
+--      writeHtmlString o{ writerSlideVariant = DZSlides
+--                       , writerHtml5 = True })
+--   ,("revealjs"      , PureStringWriter $ \o ->
+--      writeHtmlString o{ writerSlideVariant = RevealJsSlides
+--                       , writerHtml5 = True })
+--   ,("docbook"      , PureStringWriter writeDocbook)
+--   ,("docbook5"     , PureStringWriter $ \o ->
+--      writeDocbook o{ writerDocbook5 = True })
+--   ,("opml"         , PureStringWriter writeOPML)
+--   ,("opendocument" , PureStringWriter writeOpenDocument)
+--   ,("latex"        , PureStringWriter writeLaTeX)
+--   ,("beamer"       , PureStringWriter $ \o ->
+--      writeLaTeX o{ writerBeamer = True })
+--   ,("context"      , PureStringWriter writeConTeXt)
+--   ,("texinfo"      , PureStringWriter writeTexinfo)
+--   ,("man"          , PureStringWriter writeMan)
+--   ,("markdown"     , PureStringWriter writeMarkdown)
+--   ,("markdown_strict" , PureStringWriter writeMarkdown)
+--   ,("markdown_phpextra" , PureStringWriter writeMarkdown)
+--   ,("markdown_github" , PureStringWriter writeMarkdown)
+--   ,("markdown_mmd" , PureStringWriter writeMarkdown)
+--   ,("plain"        , PureStringWriter writePlain)
+--   ,("rst"          , PureStringWriter writeRST)
+--   ,("mediawiki"    , PureStringWriter writeMediaWiki)
+--   ,("dokuwiki"     , PureStringWriter writeDokuWiki)
+--   ,("zimwiki"      , PureStringWriter writeZimWiki)
+--   ,("textile"      , PureStringWriter writeTextile)
+--   ,("rtf"          , IOStringWriter $ \o doc ->
+--                       runIOorExplode $ writeRTFWithEmbeddedImages o doc)
+--   ,("org"          , PureStringWriter writeOrg)
+--   ,("asciidoc"     , PureStringWriter writeAsciiDoc)
+--   ,("haddock"      , PureStringWriter writeHaddock)
+--   ,("commonmark"   , PureStringWriter writeCommonMark)
+--   ,("tei"          , PureStringWriter writeTEI)
+--   ]
+
+data Writer' m = StringWriter' (WriterOptions -> Pandoc -> m String)
+               | ByteStringWriter' (WriterOptions -> Pandoc -> m BL.ByteString)
 
 -- | Association list of formats and writers.
-writers :: [ ( String, Writer ) ]
-writers = [
-   ("native"       , PureStringWriter writeNative)
-  ,("json"         , PureStringWriter writeJSON)
-  ,("docx"         , IOByteStringWriter $ \o doc ->
-                      runIOorExplode $ writeDocx o doc)
-  ,("odt"          , IOByteStringWriter $ \o doc ->
-                      runIOorExplode $ writeODT o doc)
-  ,("epub"         , IOByteStringWriter $ \o doc ->
-                      runIOorExplode $
-                      writeEPUB o{ writerEpubVersion = Just EPUB2 } doc)
-  ,("epub3"        , IOByteStringWriter $ \o doc ->
-                      runIOorExplode $ 
-                      writeEPUB o{ writerEpubVersion = Just EPUB3 } doc)
-  ,("fb2"          , IOStringWriter $ \o doc ->
-                      runIOorExplode $ writeFB2 o doc)
-  ,("html"         , PureStringWriter writeHtmlString)
-  ,("html5"        , PureStringWriter $ \o ->
+writers' :: PandocMonad m => [ ( String, Writer' m) ]
+writers' = [
+   ("native"       , StringWriter' writeNative)
+  ,("json"         , StringWriter' $ \o d -> return $ writeJSON o d)
+  ,("docx"         , ByteStringWriter' writeDocx)
+  ,("odt"          , ByteStringWriter' writeODT)
+  ,("epub"         , ByteStringWriter' $ \o ->
+                      writeEPUB o{ writerEpubVersion = Just EPUB2 })
+  ,("epub3"        , ByteStringWriter' $ \o ->
+                      writeEPUB o{ writerEpubVersion = Just EPUB3 })
+  ,("fb2"          , StringWriter' writeFB2)
+  ,("html"         , StringWriter' writeHtmlString)
+  ,("html5"        , StringWriter' $ \o ->
      writeHtmlString o{ writerHtml5 = True })
-  ,("icml"         , IOStringWriter $ \o doc ->
-                      runIOorExplode $ writeICML o doc)
-  ,("s5"           , PureStringWriter $ \o ->
+  ,("icml"         , StringWriter' writeICML)
+  ,("s5"           , StringWriter' $ \o ->
      writeHtmlString o{ writerSlideVariant = S5Slides
                       , writerTableOfContents = False })
-  ,("slidy"        , PureStringWriter $ \o ->
+  ,("slidy"        , StringWriter' $ \o ->
      writeHtmlString o{ writerSlideVariant = SlidySlides })
-  ,("slideous"     , PureStringWriter $ \o ->
+  ,("slideous"     , StringWriter' $ \o ->
      writeHtmlString o{ writerSlideVariant = SlideousSlides })
-  ,("dzslides"     , PureStringWriter $ \o ->
+  ,("dzslides"     , StringWriter' $ \o ->
      writeHtmlString o{ writerSlideVariant = DZSlides
                       , writerHtml5 = True })
-  ,("revealjs"      , PureStringWriter $ \o ->
+  ,("revealjs"      , StringWriter' $ \o ->
      writeHtmlString o{ writerSlideVariant = RevealJsSlides
                       , writerHtml5 = True })
-  ,("docbook"      , PureStringWriter writeDocbook)
-  ,("docbook5"     , PureStringWriter $ \o ->
+  ,("docbook"      , StringWriter' writeDocbook)
+  ,("docbook5"     , StringWriter' $ \o ->
      writeDocbook o{ writerDocbook5 = True })
-  ,("opml"         , PureStringWriter writeOPML)
-  ,("opendocument" , PureStringWriter writeOpenDocument)
-  ,("latex"        , PureStringWriter writeLaTeX)
-  ,("beamer"       , PureStringWriter $ \o ->
+  ,("opml"         , StringWriter' writeOPML)
+  ,("opendocument" , StringWriter' writeOpenDocument)
+  ,("latex"        , StringWriter' writeLaTeX)
+  ,("beamer"       , StringWriter' $ \o ->
      writeLaTeX o{ writerBeamer = True })
-  ,("context"      , PureStringWriter writeConTeXt)
-  ,("texinfo"      , PureStringWriter writeTexinfo)
-  ,("man"          , PureStringWriter writeMan)
-  ,("markdown"     , PureStringWriter writeMarkdown)
-  ,("markdown_strict" , PureStringWriter writeMarkdown)
-  ,("markdown_phpextra" , PureStringWriter writeMarkdown)
-  ,("markdown_github" , PureStringWriter writeMarkdown)
-  ,("markdown_mmd" , PureStringWriter writeMarkdown)
-  ,("plain"        , PureStringWriter writePlain)
-  ,("rst"          , PureStringWriter writeRST)
-  ,("mediawiki"    , PureStringWriter writeMediaWiki)
-  ,("dokuwiki"     , PureStringWriter writeDokuWiki)
-  ,("zimwiki"      , PureStringWriter writeZimWiki)
-  ,("textile"      , PureStringWriter writeTextile)
-  ,("rtf"          , IOStringWriter $ \o doc ->
-                      runIOorExplode $ writeRTFWithEmbeddedImages o doc)
-  ,("org"          , PureStringWriter writeOrg)
-  ,("asciidoc"     , PureStringWriter writeAsciiDoc)
-  ,("haddock"      , PureStringWriter writeHaddock)
-  ,("commonmark"   , PureStringWriter writeCommonMark)
-  ,("tei"          , PureStringWriter writeTEI)
+  ,("context"      , StringWriter' writeConTeXt)
+  ,("texinfo"      , StringWriter' writeTexinfo)
+  ,("man"          , StringWriter' writeMan)
+  ,("markdown"     , StringWriter' writeMarkdown)
+  ,("markdown_strict" , StringWriter' writeMarkdown)
+  ,("markdown_phpextra" , StringWriter' writeMarkdown)
+  ,("markdown_github" , StringWriter' writeMarkdown)
+  ,("markdown_mmd" , StringWriter' writeMarkdown)
+  ,("plain"        , StringWriter' writePlain)
+  ,("rst"          , StringWriter' writeRST)
+  ,("mediawiki"    , StringWriter' writeMediaWiki)
+  ,("dokuwiki"     , StringWriter' writeDokuWiki)
+  ,("zimwiki"      , StringWriter' writeZimWiki)
+  ,("textile"      , StringWriter' writeTextile)
+  ,("rtf"          , StringWriter' $ \o ->
+     writeRTFWithEmbeddedImages o)
+  ,("org"          , StringWriter' writeOrg)
+  ,("asciidoc"     , StringWriter' writeAsciiDoc)
+  ,("haddock"      , StringWriter' writeHaddock)
+  ,("commonmark"   , StringWriter' writeCommonMark)
+  ,("tei"          , StringWriter' writeTEI)
   ]
 
 getDefaultExtensions :: String -> Set Extension
@@ -368,20 +434,34 @@ getReader s =
                                             getDefaultExtensions readerName }
 
 -- | Retrieve writer based on formatSpec (format+extensions).
-getWriter :: String -> Either String Writer
-getWriter s
+-- getWriter :: String -> Either String Writer
+-- getWriter s
+--   = case parseFormatSpec s of
+--          Left e  -> Left $ intercalate "\n" [m | Message m <- errorMessages e]
+--          Right (writerName, setExts) ->
+--              case lookup writerName writers of
+--                      Nothing -> Left $ "Unknown writer: " ++ writerName
+--                      Just (PureStringWriter r) -> Right $ PureStringWriter $
+--                              \o -> r o{ writerExtensions = setExts $
+--                                               getDefaultExtensions writerName }
+--                      Just (IOStringWriter r) -> Right $ IOStringWriter $
+--                              \o -> r o{ writerExtensions = setExts $
+--                                               getDefaultExtensions writerName }
+--                      Just (IOByteStringWriter r) -> Right $ IOByteStringWriter $
+--                              \o -> r o{ writerExtensions = setExts $
+--                                               getDefaultExtensions writerName }
+
+getWriter' :: PandocMonad m => String -> Either String (Writer' m)
+getWriter' s
   = case parseFormatSpec s of
          Left e  -> Left $ intercalate "\n" [m | Message m <- errorMessages e]
          Right (writerName, setExts) ->
-             case lookup writerName writers of
+             case lookup writerName writers' of
                      Nothing -> Left $ "Unknown writer: " ++ writerName
-                     Just (PureStringWriter r) -> Right $ PureStringWriter $
-                             \o -> r o{ writerExtensions = setExts $
-                                              getDefaultExtensions writerName }
-                     Just (IOStringWriter r) -> Right $ IOStringWriter $
+                     Just (StringWriter' r) -> Right $ StringWriter' $
                              \o -> r o{ writerExtensions = setExts $
                                               getDefaultExtensions writerName }
-                     Just (IOByteStringWriter r) -> Right $ IOByteStringWriter $
+                     Just (ByteStringWriter' r) -> Right $ ByteStringWriter' $
                              \o -> r o{ writerExtensions = setExts $
                                               getDefaultExtensions writerName }