8 files changed, 38 insertions, 32 deletions
diff --git a/src/Text/Pandoc/Lua/Filter.hs b/src/Text/Pandoc/Lua/Filter.hs
index 9416bf41f..74c7058f3 100644
--- a/src/Text/Pandoc/Lua/Filter.hs
+++ b/src/Text/Pandoc/Lua/Filter.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE FlexibleContexts  #-}
 {-# LANGUAGE NoImplicitPrelude #-}
 {- |
 Module      : Text.Pandoc.Lua.Filter
@@ -180,7 +180,7 @@ constructorsFor :: DataType -> [String]
 constructorsFor x = map show (dataTypeConstrs x)
 
 inlineElementNames :: [String]
-inlineElementNames = "Inline" : constructorsFor (dataTypeOf (Str []))
+inlineElementNames = "Inline" : constructorsFor (dataTypeOf (Str mempty))
 
 blockElementNames :: [String]
 blockElementNames = "Block" : constructorsFor (dataTypeOf (Para []))
diff --git a/src/Text/Pandoc/Lua/Global.hs b/src/Text/Pandoc/Lua/Global.hs
index b9b6c9cd9..20963f831 100644
--- a/src/Text/Pandoc/Lua/Global.hs
+++ b/src/Text/Pandoc/Lua/Global.hs
@@ -27,11 +27,12 @@ import Text.Pandoc.Lua.Marshaling ()
 import Text.Pandoc.Lua.Util (addFunction)
 import Text.Pandoc.Options (ReaderOptions)
 
+import qualified Data.Text as Text
 import qualified Foreign.Lua as Lua
 
 -- | Permissible global Lua variables.
 data Global =
-    FORMAT String
+    FORMAT Text.Text
   | PANDOC_API_VERSION
   | PANDOC_DOCUMENT Pandoc
   | PANDOC_READER_OPTIONS ReaderOptions
diff --git a/src/Text/Pandoc/Lua/Init.hs b/src/Text/Pandoc/Lua/Init.hs
index f1cab7e82..cf6c71231 100644
--- a/src/Text/Pandoc/Lua/Init.hs
+++ b/src/Text/Pandoc/Lua/Init.hs
@@ -28,13 +28,14 @@ import Text.Pandoc.Lua.Packages (LuaPackageParams (..),
                                  installPandocPackageSearcher)
 import Text.Pandoc.Lua.Util (loadScriptFromDataDir)
 
+import qualified Data.Text as Text
 import qualified Foreign.Lua as Lua
 import qualified Foreign.Lua.Module.Text as Lua
 import qualified Text.Pandoc.Definition as Pandoc
 import qualified Text.Pandoc.Lua.Module.Pandoc as ModulePandoc
 
 -- | Lua error message
-newtype LuaException = LuaException String deriving (Show)
+newtype LuaException = LuaException Text.Text deriving (Show)
 
 -- | Run the lua interpreter, using pandoc's default way of environment
 -- initialization.
@@ -56,7 +57,7 @@ runLua luaOp = do
     return (opResult, st)
   liftIO $ setForeignEncoding enc
   case res of
-    Left (Lua.Exception msg) -> return $ Left (LuaException msg)
+    Left (Lua.Exception msg) -> return $ Left (LuaException $ Text.pack msg)
     Right (x, newState) -> do
       putCommonState newState
       return $ Right x
diff --git a/src/Text/Pandoc/Lua/Marshaling/CommonState.hs b/src/Text/Pandoc/Lua/Marshaling/CommonState.hs
index eed1500ec..b65396f68 100644
--- a/src/Text/Pandoc/Lua/Marshaling/CommonState.hs
+++ b/src/Text/Pandoc/Lua/Marshaling/CommonState.hs
@@ -1,6 +1,7 @@
 {-# OPTIONS_GHC -fno-warn-orphans #-}
 {-# LANGUAGE LambdaCase           #-}
 {-# LANGUAGE NoImplicitPrelude    #-}
+{-# LANGUAGE OverloadedStrings    #-}
 {- |
    Module      : Text.Pandoc.Lua.Marshaling.CommonState
    Copyright   : © 2012-2019 John MacFarlane
@@ -23,6 +24,7 @@ import Text.Pandoc.Logging (LogMessage, showLogMessage)
 import Text.Pandoc.Lua.Marshaling.AnyValue (AnyValue (..))
 
 import qualified Data.Map as Map
+import qualified Data.Text as Text
 import qualified Foreign.Lua as Lua
 import qualified Text.Pandoc.Lua.Util as LuaUtil
 
@@ -46,7 +48,7 @@ indexCommonState st (AnyValue idx) = Lua.ltype idx >>= \case
   Lua.TypeString -> 1 <$ (Lua.peek idx >>= pushField)
   _ -> 1 <$ Lua.pushnil
  where
-  pushField :: String -> Lua ()
+  pushField :: Text.Text -> Lua ()
   pushField name = case lookup name commonStateFields of
     Just pushValue -> pushValue st
     Nothing -> Lua.pushnil
@@ -71,7 +73,7 @@ pairsCommonState st = do
           (nextKey, pushValue):_ -> 2 <$ (Lua.push nextKey *> pushValue st)
       _ -> 2 <$ (Lua.pushnil *> Lua.pushnil)
 
-commonStateFields :: [(String, CommonState -> Lua ())]
+commonStateFields :: [(Text.Text, CommonState -> Lua ())]
 commonStateFields =
   [ ("input_files", Lua.push . stInputFiles)
   , ("output_file", Lua.push . Lua.Optional . stOutputFile)
@@ -98,5 +100,5 @@ instance Pushable LogMessage where
     pushLogMessageMetatable = ensureUserdataMetatable logMessageTypeName $
       LuaUtil.addFunction "__tostring" tostringLogMessage
 
-tostringLogMessage :: LogMessage -> Lua String
+tostringLogMessage :: LogMessage -> Lua Text.Text
 tostringLogMessage = return . showLogMessage
diff --git a/src/Text/Pandoc/Lua/Marshaling/ReaderOptions.hs b/src/Text/Pandoc/Lua/Marshaling/ReaderOptions.hs
index 5395f6fc8..226fe2e71 100644
--- a/src/Text/Pandoc/Lua/Marshaling/ReaderOptions.hs
+++ b/src/Text/Pandoc/Lua/Marshaling/ReaderOptions.hs
@@ -25,6 +25,7 @@ import Text.Pandoc.Lua.Marshaling.CommonState ()
 import Text.Pandoc.Options (ReaderOptions (..), TrackChanges)
 
 import qualified Data.Set as Set
+import qualified Data.Text as Text
 import qualified Foreign.Lua as Lua
 import qualified Text.Pandoc.Lua.Util as LuaUtil
 
@@ -44,9 +45,9 @@ instance Pushable ReaderOptions where
           (standalone            :: Bool)
           (columns               :: Int)
           (tabStop               :: Int)
-          (indentedCodeClasses   :: [String])
-          (abbreviations         :: Set.Set String)
-          (defaultImageExtension :: String)
+          (indentedCodeClasses   :: [Text.Text])
+          (abbreviations         :: Set.Set Text.Text)
+          (defaultImageExtension :: Text.Text)
           (trackChanges          :: TrackChanges)
           (stripComments         :: Bool)
           = ro
diff --git a/src/Text/Pandoc/Lua/Module/MediaBag.hs b/src/Text/Pandoc/Lua/Module/MediaBag.hs
index 261785665..951571ddd 100644
--- a/src/Text/Pandoc/Lua/Module/MediaBag.hs
+++ b/src/Text/Pandoc/Lua/Module/MediaBag.hs
@@ -15,7 +15,6 @@ module Text.Pandoc.Lua.Module.MediaBag
 
 import Prelude
 import Control.Monad (zipWithM_)
-import Data.Maybe (fromMaybe)
 import Foreign.Lua (Lua, NumResults, Optional, liftIO)
 import Text.Pandoc.Class (CommonState (..), fetchItem, putCommonState,
                           runIOorExplode, setMediaBag)
@@ -25,6 +24,7 @@ import Text.Pandoc.Lua.Util (addFunction)
 import Text.Pandoc.MIME (MimeType)
 
 import qualified Data.ByteString.Lazy as BL
+import qualified Data.Text as T
 import qualified Foreign.Lua as Lua
 import qualified Text.Pandoc.MediaBag as MB
 
@@ -113,7 +113,7 @@ mediaDirectoryFn = do
     Lua.push "length" *> Lua.push contentLength *> Lua.rawset (-3)
     Lua.rawseti (-2) idx
 
-fetch :: String
+fetch :: T.Text
       -> Lua NumResults
 fetch src = do
   commonState <- getCommonState
@@ -122,6 +122,6 @@ fetch src = do
     putCommonState commonState
     setMediaBag mediaBag
     fetchItem src
-  Lua.push $ fromMaybe "" mimeType
+  Lua.push $ maybe "" T.unpack mimeType
   Lua.push bs
   return 2 -- returns 2 values: contents, mimetype
diff --git a/src/Text/Pandoc/Lua/Module/Pandoc.hs b/src/Text/Pandoc/Lua/Module/Pandoc.hs
index 182008da7..36d6f4009 100644
--- a/src/Text/Pandoc/Lua/Module/Pandoc.hs
+++ b/src/Text/Pandoc/Lua/Module/Pandoc.hs
@@ -1,5 +1,6 @@
-{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE FlexibleContexts  #-}
 {-# LANGUAGE NoImplicitPrelude #-}
+{-# LANGUAGE OverloadedStrings #-}
 {- |
    Module      : Text.Pandoc.Lua.Module.Pandoc
    Copyright   : Copyright © 2017-2019 Albert Krewinkel
@@ -19,7 +20,6 @@ import Control.Monad (when)
 import Control.Monad.Except (throwError)
 import Data.Default (Default (..))
 import Data.Maybe (fromMaybe)
-import Data.Text (pack)
 import Foreign.Lua (Lua, NumResults, Optional, Peekable, Pushable)
 import System.Exit (ExitCode (..))
 import Text.Pandoc.Class (runIO)
@@ -33,6 +33,7 @@ import Text.Pandoc.Readers (Reader (..), getReader)
 
 import qualified Data.ByteString.Lazy as BL
 import qualified Data.ByteString.Lazy.Char8 as BSL
+import qualified Data.Text as T
 import qualified Foreign.Lua as Lua
 import qualified Text.Pandoc.Lua.Util as LuaUtil
 import Text.Pandoc.Error
@@ -59,22 +60,22 @@ walkInline = walkElement
 walkBlock :: Block -> LuaFilter -> Lua Block
 walkBlock = walkElement
 
-readDoc :: String -> Optional String -> Lua NumResults
+readDoc :: T.Text -> Optional T.Text -> Lua NumResults
 readDoc content formatSpecOrNil = do
   let formatSpec = fromMaybe "markdown" (Lua.fromOptional formatSpecOrNil)
   res <- Lua.liftIO . runIO $
            getReader formatSpec >>= \(rdr,es) ->
              case rdr of
                TextReader r ->
-                 r def{ readerExtensions = es } (pack content)
+                 r def{ readerExtensions = es } content
                _ -> throwError $ PandocSomeError $
                       "Only textual formats are supported"
   case res of
     Right pd -> (1 :: NumResults) <$ Lua.push pd -- success, push Pandoc
     Left  (PandocUnknownReaderError f) -> Lua.raiseError $
-       "Unknown reader: " ++ f
+       "Unknown reader: " <> f
     Left  (PandocUnsupportedExtensionError e f) -> Lua.raiseError $
-       "Extension " ++ e ++ " not supported for " ++ f
+       "Extension " <> e <> " not supported for " <> f
     Left  e      -> Lua.raiseError $ show e
 
 -- | Pipes input through a command.
@@ -86,10 +87,10 @@ pipeFn command args input = do
   (ec, output) <- Lua.liftIO $ pipeProcess Nothing command args input
   case ec of
     ExitSuccess -> 1 <$ Lua.push output
-    ExitFailure n -> Lua.raiseError (PipeError command n output)
+    ExitFailure n -> Lua.raiseError (PipeError (T.pack command) n output)
 
 data PipeError = PipeError
-  { pipeErrorCommand :: String
+  { pipeErrorCommand :: T.Text
   , pipeErrorCode :: Int
   , pipeErrorOutput :: BL.ByteString
   }
@@ -118,7 +119,7 @@ instance Pushable PipeError where
         pipeErrorMessage :: PipeError -> Lua BL.ByteString
         pipeErrorMessage (PipeError cmd errorCode output) = return $ mconcat
           [ BSL.pack "Error running "
-          , BSL.pack cmd
+          , BSL.pack $ T.unpack cmd
           , BSL.pack " (error code "
           , BSL.pack $ show errorCode
           , BSL.pack "): "
diff --git a/src/Text/Pandoc/Lua/Module/Utils.hs b/src/Text/Pandoc/Lua/Module/Utils.hs
index 057e6580b..7d6dd0fab 100644
--- a/src/Text/Pandoc/Lua/Module/Utils.hs
+++ b/src/Text/Pandoc/Lua/Module/Utils.hs
@@ -15,7 +15,6 @@ module Text.Pandoc.Lua.Module.Utils
 
 import Prelude
 import Control.Applicative ((<|>))
-import Data.Char (toLower)
 import Data.Default (def)
 import Data.Version (Version)
 import Foreign.Lua (Peekable, Lua, NumResults)
@@ -27,6 +26,7 @@ import Text.Pandoc.Lua.Util (addFunction)
 
 import qualified Data.Digest.Pure.SHA as SHA
 import qualified Data.ByteString.Lazy as BSL
+import qualified Data.Text as T
 import qualified Foreign.Lua as Lua
 import qualified Text.Pandoc.Builder as B
 import qualified Text.Pandoc.Filter.JSON as JSONFilter
@@ -64,7 +64,7 @@ makeSections number baselevel =
 -- limit years to the range 1601-9999 (ISO 8601 accepts greater than
 -- or equal to 1583, but MS Word only accepts dates starting 1601).
 -- Returns nil instead of a string if the conversion failed.
-normalizeDate :: String -> Lua (Lua.Optional String)
+normalizeDate :: T.Text -> Lua (Lua.Optional T.Text)
 normalizeDate = return . Lua.Optional . Shared.normalizeDate
 
 -- | Run a JSON filter on the given document.
@@ -88,13 +88,13 @@ runJSONFilter mbDatadir doc filterFile optArgs = do
 
 -- | Calculate the hash of the given contents.
 sha1 :: BSL.ByteString
-     -> Lua String
-sha1 = return . SHA.showDigest . SHA.sha1
+     -> Lua T.Text
+sha1 = return . T.pack . SHA.showDigest . SHA.sha1
 
 -- | Convert pandoc structure to a string with formatting removed.
 -- Footnotes are skipped (since we don't want their contents in link
 -- labels).
-stringify :: AstElement -> Lua String
+stringify :: AstElement -> Lua T.Text
 stringify el = return $ case el of
   PandocElement pd -> Shared.stringify pd
   InlineElement i  -> Shared.stringify i
@@ -102,11 +102,11 @@ stringify el = return $ case el of
   MetaElement m    -> Shared.stringify m
   CitationElement c  -> Shared.stringify c
   MetaValueElement m -> stringifyMetaValue m
-  _                  -> ""
+  _                  -> mempty
 
-stringifyMetaValue :: MetaValue -> String
+stringifyMetaValue :: MetaValue -> T.Text
 stringifyMetaValue mv = case mv of
-  MetaBool b   -> map toLower (show b)
+  MetaBool b   -> T.toLower $ T.pack (show b)
   MetaString s -> s
   _            -> Shared.stringify mv
 
@@ -139,5 +139,5 @@ instance Peekable AstElement where
         "Expected an AST element, but could not parse value as such."
 
 -- | Convert a number < 4000 to uppercase roman numeral.
-toRomanNumeral :: Lua.Integer -> Lua String
+toRomanNumeral :: Lua.Integer -> Lua T.Text
 toRomanNumeral = return . Shared.toRomanNumeral . fromIntegral