4 files changed, 111 insertions, 107 deletions
diff --git a/src/Text/Pandoc/App/CommandLineOptions.hs b/src/Text/Pandoc/App/CommandLineOptions.hs
index c6f88af24..56b1f780a 100644
--- a/src/Text/Pandoc/App/CommandLineOptions.hs
+++ b/src/Text/Pandoc/App/CommandLineOptions.hs
@@ -2,6 +2,7 @@
 {-# LANGUAGE CPP                 #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TupleSections       #-}
+{-# LANGUAGE OverloadedStrings   #-}
 {- |
    Module      : Text.Pandoc.App.CommandLineOptions
    Copyright   : Copyright (C) 2006-2019 John MacFarlane
@@ -45,7 +46,7 @@ import Text.Pandoc.Builder (setMeta)
 import Text.Pandoc.App.Opt (Opt (..), LineEnding (..), IpynbOutput (..))
 import Text.Pandoc.Filter (Filter (..))
 import Text.Pandoc.Highlighting (highlightingStyles)
-import Text.Pandoc.Shared (ordNub, safeRead, defaultUserDataDirs)
+import Text.Pandoc.Shared (ordNub, elemText, safeStrRead, defaultUserDataDirs)
 import Text.Printf
 
 #ifdef EMBED_DATA_FILES
@@ -78,7 +79,7 @@ parseOptions options' defaults = do
        unrecognizedOpts
 
   unless (null errors && null unknownOptionErrors) $
-     E.throwIO $ PandocOptionError $
+     E.throwIO $ PandocOptionError $ T.pack $
         concat errors ++ unlines unknownOptionErrors ++
         ("Try " ++ prg ++ " --help for more information.")
 
@@ -92,7 +93,7 @@ latexEngines  = ["pdflatex", "lualatex", "xelatex", "latexmk", "tectonic"]
 htmlEngines :: [String]
 htmlEngines  = ["wkhtmltopdf", "weasyprint", "prince"]
 
-engines :: [(String, String)]
+engines :: [(Text, String)]
 engines = map ("html",) htmlEngines ++
           map ("html5",) htmlEngines ++
           map ("latex",) latexEngines ++
@@ -119,13 +120,13 @@ options =
     [ Option "fr" ["from","read"]
                  (ReqArg
                   (\arg opt -> return opt { optFrom =
-                                              Just (map toLower arg) })
+                                              Just (T.toLower $ T.pack arg) })
                   "FORMAT")
                  ""
 
     , Option "tw" ["to","write"]
                  (ReqArg
-                  (\arg opt -> return opt { optTo = Just arg })
+                  (\arg opt -> return opt { optTo = Just $ T.pack arg })
                   "FORMAT")
                  ""
 
@@ -218,7 +219,7 @@ options =
     , Option "" ["toc-depth"]
                  (ReqArg
                   (\arg opt ->
-                      case safeRead arg of
+                      case safeStrRead arg of
                            Just t | t >= 1 && t <= 6 ->
                                     return opt { optTOCDepth = t }
                            _ -> E.throwIO $ PandocOptionError
@@ -234,7 +235,7 @@ options =
     , Option "" ["number-offset"]
                  (ReqArg
                   (\arg opt ->
-                      case safeRead ('[':arg ++ "]") of
+                      case safeStrRead ("[" <> arg <> "]") of
                            Just ns -> return opt { optNumberOffset = ns,
                                                    optNumberSections = True }
                            _      -> E.throwIO $ PandocOptionError
@@ -255,7 +256,7 @@ options =
                         "default" -> return opt{ optTopLevelDivision =
                                         TopLevelDefault }
                         _ -> E.throwIO $ PandocOptionError $
-                                "Top-level division must be " ++
+                                "Top-level division must be " <>
                                 "section,  chapter, part, or default" )
                    "section|chapter|part")
                  "" -- "Use top-level division type in LaTeX, ConTeXt, DocBook"
@@ -307,7 +308,7 @@ options =
     , Option "" ["highlight-style"]
                 (ReqArg
                  (\arg opt ->
-                     return opt{ optHighlightStyle = Just arg })
+                     return opt{ optHighlightStyle = Just $ T.pack arg })
                  "STYLE|FILE")
                  "" -- "Style for highlighted code"
 
@@ -328,7 +329,7 @@ options =
     , Option "" ["dpi"]
                  (ReqArg
                   (\arg opt ->
-                    case safeRead arg of
+                    case safeStrRead arg of
                          Just t | t > 0 -> return opt { optDpi = t }
                          _              -> E.throwIO $ PandocOptionError
                                         "dpi must be a number greater than 0")
@@ -351,7 +352,7 @@ options =
     , Option "" ["columns"]
                  (ReqArg
                   (\arg opt ->
-                      case safeRead arg of
+                      case safeStrRead arg of
                            Just t | t > 0 -> return opt { optColumns = t }
                            _              -> E.throwIO $ PandocOptionError
                                    "columns must be a number greater than 0")
@@ -366,7 +367,7 @@ options =
     , Option "" ["tab-stop"]
                  (ReqArg
                   (\arg opt ->
-                      case safeRead arg of
+                      case safeStrRead arg of
                            Just t | t > 0 -> return opt { optTabStop = t }
                            _              -> E.throwIO $ PandocOptionError
                                   "tab-stop must be a number greater than 0")
@@ -379,7 +380,7 @@ options =
                      let b = takeBaseName arg
                      if b `elem` pdfEngines
                         then return opt { optPdfEngine = Just arg }
-                        else E.throwIO $ PandocOptionError $ "pdf-engine must be one of "
+                        else E.throwIO $ PandocOptionError $ T.pack $ "pdf-engine must be one of "
                                ++ intercalate ", " pdfEngines)
                   "PROGRAM")
                  "" -- "Name of program to use in generating PDF"
@@ -410,7 +411,7 @@ options =
                   (\arg opt -> do
                      let (key, val) = splitField arg
                      return opt{ optRequestHeaders =
-                       (key, val) : optRequestHeaders opt })
+                       (T.pack key, T.pack val) : optRequestHeaders opt })
                   "NAME:VALUE")
                  ""
 
@@ -422,14 +423,15 @@ options =
 
     , Option "" ["indented-code-classes"]
                   (ReqArg
-                   (\arg opt -> return opt { optIndentedCodeClasses = words $
-                                             map (\c -> if c == ',' then ' ' else c) arg })
+                   (\arg opt -> return opt { optIndentedCodeClasses = T.words $
+                                             T.map (\c -> if c == ',' then ' ' else c) $
+                                             T.pack arg })
                    "STRING")
                   "" -- "Classes (whitespace- or comma-separated) to use for indented code-blocks"
 
     , Option "" ["default-image-extension"]
                  (ReqArg
-                  (\arg opt -> return opt { optDefaultImageExtension = arg })
+                  (\arg opt -> return opt { optDefaultImageExtension = T.pack arg })
                    "extension")
                   "" -- "Default extension for extensionless images"
 
@@ -450,7 +452,7 @@ options =
     , Option "" ["shift-heading-level-by"]
                  (ReqArg
                   (\arg opt ->
-                      case safeRead arg of
+                      case safeStrRead arg of
                            Just t ->
                                return opt{ optShiftHeadingLevelBy = t }
                            _              -> E.throwIO $ PandocOptionError
@@ -463,7 +465,7 @@ options =
                   (\arg opt -> do
                       deprecatedOption "--base-header-level"
                         "Use --shift-heading-level-by instead."
-                      case safeRead arg of
+                      case safeStrRead arg of
                            Just t | t > 0 && t < 6 ->
                                return opt{ optShiftHeadingLevelBy = t - 1 }
                            _              -> E.throwIO $ PandocOptionError
@@ -486,7 +488,7 @@ options =
                             "accept" -> return AcceptChanges
                             "reject" -> return RejectChanges
                             "all"    -> return AllChanges
-                            _        -> E.throwIO $ PandocOptionError
+                            _        -> E.throwIO $ PandocOptionError $ T.pack
                                ("Unknown option for track-changes: " ++ arg)
                      return opt { optTrackChanges = action })
                   "accept|reject|all")
@@ -509,7 +511,7 @@ options =
                             "block"    -> return EndOfBlock
                             "section"  -> return EndOfSection
                             "document" -> return EndOfDocument
-                            _        -> E.throwIO $ PandocOptionError
+                            _        -> E.throwIO $ PandocOptionError $ T.pack
                                ("Unknown option for reference-location: " ++ arg)
                      return opt { optReferenceLocation = action })
                   "block|section|document")
@@ -533,7 +535,7 @@ options =
     , Option "" ["slide-level"]
                  (ReqArg
                   (\arg opt ->
-                      case safeRead arg of
+                      case safeStrRead arg of
                            Just t | t >= 1 && t <= 6 ->
                                     return opt { optSlideLevel = Just t }
                            _      -> E.throwIO $ PandocOptionError
@@ -559,7 +561,7 @@ options =
                             "references" -> return ReferenceObfuscation
                             "javascript" -> return JavascriptObfuscation
                             "none"       -> return NoObfuscation
-                            _            -> E.throwIO $ PandocOptionError
+                            _            -> E.throwIO $ PandocOptionError $ T.pack
                                ("Unknown obfuscation method: " ++ arg)
                      return opt { optEmailObfuscation = method })
                   "none|javascript|references")
@@ -567,7 +569,7 @@ options =
 
      , Option "" ["id-prefix"]
                   (ReqArg
-                   (\arg opt -> return opt { optIdentifierPrefix = arg })
+                   (\arg opt -> return opt { optIdentifierPrefix = T.pack arg })
                    "STRING")
                   "" -- "Prefix to add to automatically generated HTML identifiers"
 
@@ -620,7 +622,7 @@ options =
     , Option "" ["epub-chapter-level"]
                  (ReqArg
                   (\arg opt ->
-                      case safeRead arg of
+                      case safeStrRead arg of
                            Just t | t >= 1 && t <= 6 ->
                                     return opt { optEpubChapterLevel = t }
                            _      -> E.throwIO $ PandocOptionError
@@ -685,15 +687,15 @@ options =
                  (OptArg
                   (\arg opt -> do
                       let url' = fromMaybe "https://latex.codecogs.com/png.latex?" arg
-                      return opt { optHTMLMathMethod = WebTeX url' })
+                      return opt { optHTMLMathMethod = WebTeX $ T.pack url' })
                   "URL")
                  "" -- "Use web service for HTML math"
 
     , Option "" ["mathjax"]
                  (OptArg
                   (\arg opt -> do
-                      let url' = fromMaybe (defaultMathJaxURL ++
-                                  "tex-mml-chtml.js") arg
+                      let url' = maybe (defaultMathJaxURL <>
+                                  "tex-mml-chtml.js") T.pack arg
                       return opt { optHTMLMathMethod = MathJax url'})
                   "URL")
                  "" -- "Use MathJax for HTML math"
@@ -703,7 +705,7 @@ options =
                   (\arg opt ->
                       return opt
                         { optHTMLMathMethod = KaTeX $
-                           fromMaybe defaultKaTeXURL arg })
+                           maybe defaultKaTeXURL T.pack arg })
                   "URL")
                   "" -- Use KaTeX for HTML Math
 
@@ -763,7 +765,7 @@ options =
                      UTF8.hPutStrLn stdout $ printf tpl allopts
                          (unwords readersNames)
                          (unwords writersNames)
-                         (unwords $ map fst highlightingStyles)
+                         (unwords $ map (T.unpack . fst) highlightingStyles)
                          (unwords datafiles)
                      exitSuccess ))
                  "" -- "Print bash completion script"
@@ -790,12 +792,12 @@ options =
                      let allExts =
                            case arg of
                              Nothing  -> extensionsFromList extList
-                             Just fmt -> getAllExtensions fmt
+                             Just fmt -> getAllExtensions $ T.pack fmt
                      let defExts =
                            case arg of
                              Nothing   -> getDefaultExtensions
                                            "markdown"
-                             Just fmt  -> getDefaultExtensions fmt
+                             Just fmt  -> getDefaultExtensions $ T.pack fmt
                      let showExt x =
                            (if extensionEnabled x defExts
                                then '+'
@@ -823,7 +825,7 @@ options =
     , Option "" ["list-highlight-styles"]
                  (NoArg
                   (\_ -> do
-                     mapM_ (UTF8.hPutStrLn stdout . fst) highlightingStyles
+                     mapM_ (UTF8.hPutStrLn stdout . T.unpack . fst) highlightingStyles
                      exitSuccess ))
                  ""
 
@@ -835,11 +837,11 @@ options =
                                         Nothing -> UTF8.hPutStr stdout
                      templ <- runIO $ do
                                 setUserDataDir Nothing
-                                getDefaultTemplate arg
+                                getDefaultTemplate (T.pack arg)
                      case templ of
                           Right t
                             | T.null t -> -- e.g. for docx, odt, json:
-                                E.throwIO $ PandocCouldNotFindDataFileError
+                                E.throwIO $ PandocCouldNotFindDataFileError $ T.pack
                                   ("templates/default." ++ arg)
                             | otherwise -> write . T.unpack $ t
                           Left e  -> E.throwIO e
@@ -890,7 +892,7 @@ options =
                   (\_ -> do
                      prg <- getProgName
                      defaultDatadirs <- defaultUserDataDirs
-                     UTF8.hPutStrLn stdout (prg ++ " " ++ pandocVersion ++
+                     UTF8.hPutStrLn stdout (prg ++ " " ++ T.unpack pandocVersion ++
                        compileInfo ++ "\nDefault user data directory: " ++
                        intercalate " or " defaultDatadirs ++
                        ('\n':copyrightMessage))
@@ -963,14 +965,14 @@ handleUnrecognizedOption x =
   (("Unknown option " ++ x ++ ".") :)
 
 readersNames :: [String]
-readersNames = sort (map fst (readers :: [(String, Reader PandocIO)]))
+readersNames = sort (map (T.unpack . fst) (readers :: [(Text, Reader PandocIO)]))
 
 writersNames :: [String]
-writersNames = sort (map fst (writers :: [(String, Writer PandocIO)]))
+writersNames = sort (map (T.unpack . fst) (writers :: [(Text, Writer PandocIO)]))
 
 splitField :: String -> (String, String)
 splitField s =
-  case break (`elem` ":=") s of
+  case break (`elemText` ":=") s of
        (k,_:v) -> (k,v)
        (k,[])  -> (k,"true")
 
@@ -991,7 +993,7 @@ applyDefaults opt file = runIOorExplode $ do
   case Y.decode1 inp of
       Right (f :: Opt -> Opt) -> return $ f opt
       Left (errpos, errmsg)  -> throwError $
-         PandocParseError $
+         PandocParseError $ T.pack $
          "Error parsing " ++ fp' ++ " line " ++
           show (Y.posLine errpos) ++ " column " ++
           show (Y.posColumn errpos) ++ ":\n" ++ errmsg
@@ -1001,18 +1003,18 @@ lookupHighlightStyle s
   | takeExtension s == ".theme" = -- attempt to load KDE theme
     do contents <- readFileLazy s
        case parseTheme contents of
-            Left _    -> throwError $ PandocOptionError $
+            Left _    -> throwError $ PandocOptionError $ T.pack $
                            "Could not read highlighting theme " ++ s
             Right sty -> return sty
   | otherwise =
-  case lookup (map toLower s) highlightingStyles of
+  case lookup (T.toLower $ T.pack s) highlightingStyles of
        Just sty -> return sty
-       Nothing  -> throwError $ PandocOptionError $
+       Nothing  -> throwError $ PandocOptionError $ T.pack $
                       "Unknown highlight-style " ++ s
 
 deprecatedOption :: String -> String -> IO ()
 deprecatedOption o msg =
-  runIO (report $ Deprecated o msg) >>=
+  runIO (report $ Deprecated (T.pack o) (T.pack msg)) >>=
     \r -> case r of
        Right () -> return ()
        Left e   -> E.throwIO e
@@ -1024,13 +1026,14 @@ setVariable key val (Context ctx) =
 
 addMeta :: String -> String -> Meta -> Meta
 addMeta k v meta =
-  case lookupMeta k meta of
-       Nothing -> setMeta k v' meta
+  case lookupMeta k' meta of
+       Nothing -> setMeta k' v' meta
        Just (MetaList xs) ->
-                  setMeta k (MetaList (xs ++ [v'])) meta
-       Just x  -> setMeta k (MetaList [x, v']) meta
+                  setMeta k' (MetaList (xs ++ [v'])) meta
+       Just x  -> setMeta k' (MetaList [x, v']) meta
  where
   v' = readMetaValue v
+  k' = T.pack k
 
 readMetaValue :: String -> MetaValue
 readMetaValue s
@@ -1040,7 +1043,7 @@ readMetaValue s
   | s == "false" = MetaBool False
   | s == "False" = MetaBool False
   | s == "FALSE" = MetaBool False
-  | otherwise    = MetaString s
+  | otherwise    = MetaString $ T.pack s
 
 -- On Windows with ghc 8.6+, we need to rewrite paths
 -- beginning with \\ to \\?\UNC\. -- See #5127.
diff --git a/src/Text/Pandoc/App/FormatHeuristics.hs b/src/Text/Pandoc/App/FormatHeuristics.hs
index a02d8d15e..25e0a303e 100644
--- a/src/Text/Pandoc/App/FormatHeuristics.hs
+++ b/src/Text/Pandoc/App/FormatHeuristics.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE NoImplicitPrelude #-}
+{-# LANGUAGE OverloadedStrings #-}
 {- |
    Module      : Text.Pandoc.App.FormatHeuristics
    Copyright   : Copyright (C) 2006-2019 John MacFarlane
@@ -16,10 +17,11 @@ module Text.Pandoc.App.FormatHeuristics
 
 import Prelude
 import Data.Char (toLower)
+import Data.Text (Text)
 import System.FilePath (takeExtension)
 
 -- Determine default format based on file extensions.
-formatFromFilePaths :: [FilePath] -> Maybe String
+formatFromFilePaths :: [FilePath] -> Maybe Text
 formatFromFilePaths [] = Nothing
 formatFromFilePaths (x:xs) =
   case formatFromFilePath x of
@@ -27,7 +29,7 @@ formatFromFilePaths (x:xs) =
     Nothing    -> formatFromFilePaths xs
 
 -- Determine format based on file extension
-formatFromFilePath :: FilePath -> Maybe String
+formatFromFilePath :: FilePath -> Maybe Text
 formatFromFilePath x =
   case takeExtension (map toLower x) of
     ".adoc"     -> Just "asciidoc"
diff --git a/src/Text/Pandoc/App/Opt.hs b/src/Text/Pandoc/App/Opt.hs
index 6db397147..c0d06e0f4 100644
--- a/src/Text/Pandoc/App/Opt.hs
+++ b/src/Text/Pandoc/App/Opt.hs
@@ -33,7 +33,7 @@ import Text.Pandoc.Options (TopLevelDivision (TopLevelDefault),
                             ReferenceLocation (EndOfDocument),
                             ObfuscationMethod (NoObfuscation),
                             CiteMethod (Citeproc))
-import Text.Pandoc.Shared (camelCaseToHyphenated)
+import Text.Pandoc.Shared (camelCaseStrToHyphenated)
 import Text.DocLayout (render)
 import Text.DocTemplates (Context(..), Val(..))
 import Data.Text (Text, unpack)
@@ -76,8 +76,8 @@ data Opt = Opt
     { optTabStop               :: Int     -- ^ Number of spaces per tab
     , optPreserveTabs          :: Bool    -- ^ Preserve tabs instead of converting to spaces
     , optStandalone            :: Bool    -- ^ Include header, footer
-    , optFrom                  :: Maybe String  -- ^ Reader format
-    , optTo                    :: Maybe String  -- ^ Writer format
+    , optFrom                  :: Maybe Text  -- ^ Reader format
+    , optTo                    :: Maybe Text  -- ^ Writer format
     , optTableOfContents       :: Bool    -- ^ Include table of contents
     , optShiftHeadingLevelBy   :: Int     -- ^ Shift heading level by
     , optTemplate              :: Maybe FilePath  -- ^ Custom template
@@ -92,7 +92,7 @@ data Opt = Opt
     , optIncremental           :: Bool    -- ^ Use incremental lists in Slidy/Slideous/S5
     , optSelfContained         :: Bool    -- ^ Make HTML accessible offline
     , optHtmlQTags             :: Bool    -- ^ Use <q> tags in HTML
-    , optHighlightStyle        :: Maybe String -- ^ Style to use for highlighted code
+    , optHighlightStyle        :: Maybe Text -- ^ Style to use for highlighted code
     , optSyntaxDefinitions     :: [FilePath]  -- ^ xml syntax defs to load
     , optTopLevelDivision      :: TopLevelDivision -- ^ Type of the top-level divisions
     , optHTMLMathMethod        :: HTMLMathMethod -- ^ Method to print HTML math
@@ -117,9 +117,9 @@ data Opt = Opt
     , optColumns               :: Int     -- ^ Line length in characters
     , optFilters               :: [Filter] -- ^ Filters to apply
     , optEmailObfuscation      :: ObfuscationMethod
-    , optIdentifierPrefix      :: String
+    , optIdentifierPrefix      :: Text
     , optStripEmptyParagraphs  :: Bool -- ^ Strip empty paragraphs
-    , optIndentedCodeClasses   :: [String] -- ^ Default classes for indented code blocks
+    , optIndentedCodeClasses   :: [Text] -- ^ Default classes for indented code blocks
     , optDataDir               :: Maybe FilePath
     , optCiteMethod            :: CiteMethod -- ^ Method to output cites
     , optListings              :: Bool       -- ^ Use listings package for code blocks
@@ -128,18 +128,18 @@ data Opt = Opt
     , optSlideLevel            :: Maybe Int  -- ^ Header level that creates slides
     , optSetextHeaders         :: Bool       -- ^ Use atx headers for markdown level 1-2
     , optAscii                 :: Bool       -- ^ Prefer ascii output
-    , optDefaultImageExtension :: String -- ^ Default image extension
+    , optDefaultImageExtension :: Text       -- ^ Default image extension
     , optExtractMedia          :: Maybe FilePath -- ^ Path to extract embedded media
     , optTrackChanges          :: TrackChanges -- ^ Accept or reject MS Word track-changes.
     , optFileScope             :: Bool         -- ^ Parse input files before combining
-    , optTitlePrefix           :: Maybe String     -- ^ Prefix for title
+    , optTitlePrefix           :: Maybe Text     -- ^ Prefix for title
     , optCss                   :: [FilePath]       -- ^ CSS files to link to
     , optIpynbOutput           :: IpynbOutput      -- ^ How to treat ipynb output blocks
     , optIncludeBeforeBody     :: [FilePath]       -- ^ Files to include before
     , optIncludeAfterBody      :: [FilePath]       -- ^ Files to include after body
     , optIncludeInHeader       :: [FilePath]       -- ^ Files to include in header
     , optResourcePath          :: [FilePath] -- ^ Path to search for images etc
-    , optRequestHeaders        :: [(String, String)] -- ^ Headers for HTTP requests
+    , optRequestHeaders        :: [(Text, Text)] -- ^ Headers for HTTP requests
     , optEol                   :: LineEnding -- ^ Style of line-endings to use
     , optStripComments         :: Bool       -- ^ Skip HTML comments
     } deriving (Generic, Show)
@@ -167,13 +167,13 @@ doOpt (k',v) = do
     "toc" ->
       parseYAML v >>= \x -> return (\o -> o{ optTableOfContents = x })
     "from" ->
-      parseYAML v >>= \x -> return (\o -> o{ optFrom = unpack <$> x })
+      parseYAML v >>= \x -> return (\o -> o{ optFrom = x })
     "reader" ->
-      parseYAML v >>= \x -> return (\o -> o{ optFrom = unpack <$> x })
+      parseYAML v >>= \x -> return (\o -> o{ optFrom = x })
     "to" ->
-      parseYAML v >>= \x -> return (\o -> o{ optTo = unpack <$> x })
+      parseYAML v >>= \x -> return (\o -> o{ optTo = x })
     "writer" ->
-      parseYAML v >>= \x -> return (\o -> o{ optTo = unpack <$> x })
+      parseYAML v >>= \x -> return (\o -> o{ optTo = x })
     "shift-heading-level-by" ->
       parseYAML v >>= \x -> return (\o -> o{ optShiftHeadingLevelBy = x })
     "template" ->
@@ -211,7 +211,7 @@ doOpt (k',v) = do
     "html-q-tags" ->
       parseYAML v >>= \x -> return (\o -> o{ optHtmlQTags = x })
     "highlight-style" ->
-      parseYAML v >>= \x -> return (\o -> o{ optHighlightStyle = unpack <$> x })
+      parseYAML v >>= \x -> return (\o -> o{ optHighlightStyle = x })
     "syntax-definition" ->
       (parseYAML v >>= \x ->
                 return (\o -> o{ optSyntaxDefinitions = map unpack x }))
@@ -274,12 +274,12 @@ doOpt (k',v) = do
       parseYAML v >>= \x -> return (\o -> o{ optEmailObfuscation = x })
     "identifier-prefix" ->
       parseYAML v >>= \x ->
-             return (\o -> o{ optIdentifierPrefix = unpack x })
+             return (\o -> o{ optIdentifierPrefix = x })
     "strip-empty-paragraphs" ->
       parseYAML v >>= \x -> return (\o -> o{ optStripEmptyParagraphs = x })
     "indented-code-classes" ->
       parseYAML v >>= \x ->
-             return (\o -> o{ optIndentedCodeClasses = map unpack x })
+             return (\o -> o{ optIndentedCodeClasses = x })
     "data-dir" ->
       parseYAML v >>= \x -> return (\o -> o{ optDataDir = unpack <$> x })
     "cite-method" ->
@@ -305,7 +305,7 @@ doOpt (k',v) = do
       parseYAML v >>= \x -> return (\o -> o{ optAscii = x })
     "default-image-extension" ->
       parseYAML v >>= \x ->
-             return (\o -> o{ optDefaultImageExtension = unpack x })
+             return (\o -> o{ optDefaultImageExtension = x })
     "extract-media" ->
       parseYAML v >>= \x ->
              return (\o -> o{ optExtractMedia = unpack <$> x })
@@ -314,7 +314,7 @@ doOpt (k',v) = do
     "file-scope" ->
       parseYAML v >>= \x -> return (\o -> o{ optFileScope = x })
     "title-prefix" ->
-      parseYAML v >>= \x -> return (\o -> o{ optTitlePrefix = unpack <$> x })
+      parseYAML v >>= \x -> return (\o -> o{ optTitlePrefix = x })
     "css" ->
       (parseYAML v >>= \x -> return (\o -> o{ optCss = map unpack x }))
       <|>
@@ -344,9 +344,7 @@ doOpt (k',v) = do
              return (\o -> o{ optResourcePath = map unpack x })
     "request-headers" ->
       parseYAML v >>= \x ->
-             return (\o -> o{ optRequestHeaders =
-                              map (\(key,val) ->
-                                     (unpack key, unpack val)) x })
+             return (\o -> o{ optRequestHeaders = x })
     "eol" ->
       parseYAML v >>= \x -> return (\o -> o{ optEol = x })
     "strip-comments" ->
@@ -429,13 +427,13 @@ defaultOpts = Opt
 
 contextToMeta :: Context Text -> Meta
 contextToMeta (Context m) =
-  Meta . M.mapKeys unpack . M.map valToMetaVal $ m
+  Meta . M.map valToMetaVal $ m
 
 valToMetaVal :: Val Text -> MetaValue
 valToMetaVal (MapVal (Context m)) =
-  MetaMap . M.mapKeys unpack . M.map valToMetaVal $ m
+  MetaMap . M.map valToMetaVal $ m
 valToMetaVal (ListVal xs) = MetaList $ map valToMetaVal xs
-valToMetaVal (SimpleVal d) = MetaString (unpack $ render Nothing d)
+valToMetaVal (SimpleVal d) = MetaString $ render Nothing d
 valToMetaVal NullVal = MetaString ""
 
 -- see https://github.com/jgm/pandoc/pull/4083
@@ -446,5 +444,5 @@ $(deriveJSON
    defaultOptions{ fieldLabelModifier = map toLower } ''LineEnding)
 $(deriveJSON
    defaultOptions{ fieldLabelModifier =
-                      camelCaseToHyphenated . dropWhile isLower
+                      camelCaseStrToHyphenated . dropWhile isLower
                  } ''Opt)
diff --git a/src/Text/Pandoc/App/OutputSettings.hs b/src/Text/Pandoc/App/OutputSettings.hs
index b29860c03..d328a9b6a 100644
--- a/src/Text/Pandoc/App/OutputSettings.hs
+++ b/src/Text/Pandoc/App/OutputSettings.hs
@@ -1,6 +1,7 @@
 {-# LANGUAGE CPP                 #-}
 {-# LANGUAGE FlexibleContexts    #-}
 {-# LANGUAGE NoImplicitPrelude   #-}
+{-# LANGUAGE OverloadedStrings   #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TupleSections       #-}
 {- |
@@ -27,7 +28,7 @@ import Control.Monad
 import Control.Monad.Except (catchError, throwError)
 import Control.Monad.Trans
 import Data.Char (toLower)
-import Data.List (find, isPrefixOf, isSuffixOf)
+import Data.List (find, isPrefixOf)
 import Data.Maybe (fromMaybe)
 import Skylighting (defaultSyntaxMap)
 import Skylighting.Parser (addSyntaxDefinition, parseSyntaxDefinition)
@@ -42,18 +43,18 @@ import Text.Pandoc.App.CommandLineOptions (engines, lookupHighlightStyle,
                                           setVariable)
 import qualified Text.Pandoc.UTF8 as UTF8
 
+readUtf8File :: PandocMonad m => FilePath -> m T.Text
+readUtf8File = fmap UTF8.toText . readFileStrict
+
 -- | Settings specifying how document output should be produced.
 data OutputSettings = OutputSettings
-  { outputFormat :: String
+  { outputFormat :: T.Text
   , outputWriter :: Writer PandocIO
-  , outputWriterName :: String
+  , outputWriterName :: T.Text
   , outputWriterOptions :: WriterOptions
   , outputPdfProgram :: Maybe String
   }
 
-readUtf8File :: PandocMonad m => FilePath -> m String
-readUtf8File = fmap UTF8.toString . readFileStrict
-
 -- | Get output settings from command line options.
 optToOutputSettings :: Opt -> PandocIO OutputSettings
 optToOutputSettings opts = do
@@ -85,33 +86,33 @@ optToOutputSettings opts = do
                      case formatFromFilePaths [outputFile] of
                            Nothing -> do
                              report $ CouldNotDeduceFormat
-                                [takeExtension outputFile] "html"
+                                [T.pack $ takeExtension outputFile] "html"
                              return ("html", Nothing)
                            Just f  -> return (f, Nothing)
 
-  let format = if ".lua" `isSuffixOf` writerName
+  let format = if ".lua" `T.isSuffixOf` writerName
                   then writerName
-                  else map toLower $ baseWriterName writerName
+                  else T.toLower $ baseWriterName writerName
 
   (writer :: Writer PandocIO, writerExts) <-
-            if ".lua" `isSuffixOf` format
+            if ".lua" `T.isSuffixOf` format
                then return (TextWriter
-                       (\o d -> writeCustom writerName o d)
+                       (\o d -> writeCustom (T.unpack writerName) o d)
                                :: Writer PandocIO, mempty)
-               else getWriter (map toLower writerName)
+               else getWriter (T.toLower writerName)
 
   let standalone = optStandalone opts || not (isTextFormat format) || pdfOutput
 
   let addSyntaxMap existingmap f = do
         res <- liftIO (parseSyntaxDefinition f)
         case res of
-              Left errstr -> throwError $ PandocSyntaxMapError errstr
+              Left errstr -> throwError $ PandocSyntaxMapError $ T.pack errstr
               Right syn   -> return $ addSyntaxDefinition syn existingmap
 
   syntaxMap <- foldM addSyntaxMap defaultSyntaxMap
                      (optSyntaxDefinitions opts)
 
-  hlStyle <- maybe (return Nothing) (fmap Just . lookupHighlightStyle)
+  hlStyle <- maybe (return Nothing) (fmap Just . lookupHighlightStyle . T.unpack)
                 (optHighlightStyle opts)
 
   let setVariableM k v = return . setVariable k v
@@ -135,15 +136,15 @@ optToOutputSettings opts = do
     >>=
     setVariableM "outputfile" outputFile
     >>=
-    setFilesVariableM "include-before" (optIncludeBeforeBody opts)
+    setFilesVariableM "include-before" (T.pack <$> optIncludeBeforeBody opts)
     >>=
-    setFilesVariableM "include-after" (optIncludeAfterBody opts)
+    setFilesVariableM "include-after" (T.pack <$> optIncludeAfterBody opts)
     >>=
-    setFilesVariableM "header-includes" (optIncludeInHeader opts)
+    setFilesVariableM "header-includes" (T.pack <$> optIncludeInHeader opts)
     >>=
     setListVariableM "css" (optCss opts)
     >>=
-    maybe return (setVariableM "title-prefix")
+    maybe return (setVariableM "title-prefix" . T.unpack)
                  (optTitlePrefix opts)
     >>=
     maybe return (setVariableM "epub-cover-image")
@@ -168,7 +169,7 @@ optToOutputSettings opts = do
                   Just tp -> do
                     -- strip off extensions
                     let tp' = case takeExtension tp of
-                                   "" -> tp <.> format
+                                   "" -> tp <.> T.unpack format
                                    _  -> tp
                     Just . UTF8.toText <$>
                           ((do surl <- stSourceURL <$> getCommonState
@@ -176,7 +177,7 @@ optToOutputSettings opts = do
                                -- unless the full URL is specified:
                                modifyCommonState $ \st -> st{
                                   stSourceURL = Nothing }
-                               (bs, _) <- fetchItem tp'
+                               (bs, _) <- fetchItem $ T.pack tp'
                                modifyCommonState $ \st -> st{
                                   stSourceURL = surl }
                                return bs)
@@ -194,7 +195,7 @@ optToOutputSettings opts = do
              Just ts -> do
                res <- compileTemplate templatePath ts
                case res of
-                 Left  e -> throwError $ PandocTemplateError e
+                 Left  e -> throwError $ PandocTemplateError $ T.pack e
                  Right t -> return $ Just t
 
   let writerOpts = def {
@@ -222,7 +223,7 @@ optToOutputSettings opts = do
         , writerSlideLevel       = optSlideLevel opts
         , writerHighlightStyle   = hlStyle
         , writerSetextHeaders    = optSetextHeaders opts
-        , writerEpubSubdirectory = optEpubSubdirectory opts
+        , writerEpubSubdirectory = T.pack $ optEpubSubdirectory opts
         , writerEpubMetadata     = epubMetadata
         , writerEpubFonts        = optEpubFonts opts
         , writerEpubChapterLevel = optEpubChapterLevel opts
@@ -239,12 +240,12 @@ optToOutputSettings opts = do
     , outputPdfProgram = maybePdfProg
     }
 
-baseWriterName :: String -> String
-baseWriterName = takeWhile (\c -> c /= '+' && c /= '-')
+baseWriterName :: T.Text -> T.Text
+baseWriterName = T.takeWhile (\c -> c /= '+' && c /= '-')
 
-pdfWriterAndProg :: Maybe String              -- ^ user-specified writer name
+pdfWriterAndProg :: Maybe T.Text              -- ^ user-specified writer name
                  -> Maybe String              -- ^ user-specified pdf-engine
-                 -> IO (String, Maybe String) -- ^ IO (writerName, maybePdfEngineProg)
+                 -> IO (T.Text, Maybe String) -- ^ IO (writerName, maybePdfEngineProg)
 pdfWriterAndProg mWriter mEngine =
   case go mWriter mEngine of
       Right (writ, prog) -> return (writ, Just prog)
@@ -256,20 +257,20 @@ pdfWriterAndProg mWriter mEngine =
       go (Just writer) (Just engine) =
            case find (== (baseWriterName writer, takeBaseName engine)) engines of
                 Just _  -> Right (writer, engine)
-                Nothing -> Left $ "pdf-engine " ++ engine ++
-                           " is not compatible with output format " ++ writer
+                Nothing -> Left $ "pdf-engine " <> T.pack engine <>
+                           " is not compatible with output format " <> writer
 
       writerForEngine eng = case [f | (f,e) <- engines, e == eng] of
                                  fmt : _ -> Right fmt
                                  []      -> Left $
-                                   "pdf-engine " ++ eng ++ " not known"
+                                   "pdf-engine " <> T.pack eng <> " not known"
 
       engineForWriter "pdf" = Left "pdf writer"
       engineForWriter w = case [e |  (f,e) <- engines, f == baseWriterName w] of
                                 eng : _ -> Right eng
                                 []      -> Left $
-                                   "cannot produce pdf output from " ++ w
+                                   "cannot produce pdf output from " <> w
 
-isTextFormat :: String -> Bool
+isTextFormat :: T.Text -> Bool
 isTextFormat s =
   s `notElem` ["odt","docx","epub2","epub3","epub","pptx","pdf"]