T.P.Shared: remove backslashEscapes, escapeStringUsing.

[API change]

These are inefficient association list lookups.
Replace with more efficient functions in the writers that
used them (with 10-25% performance improvements in
haddock, org, rtf, texinfo writers).

src/Text/Pandoc/Shared.hs

@@ -26,8 +26,6 @@ module Text.Pandoc.Shared (
                      findM,
                      -- * Text processing
                      tshow,
-                     backslashEscapes,
-                     escapeStringUsing,
                      elemText,
                      notElemText,
                      stripTrailingNewlines,
@@ -184,17 +182,6 @@ findM p = foldr go (pure Nothing)
 tshow :: Show a => a -> T.Text
 tshow = T.pack . show
 
--- | Returns an association list of backslash escapes for the
--- designated characters.
-backslashEscapes :: [Char]    -- ^ list of special characters to escape
-                 -> [(Char, T.Text)]
-backslashEscapes = map (\ch -> (ch, T.pack ['\\',ch]))
-
--- | Escape a string of characters, using an association list of
--- characters and strings.
-escapeStringUsing :: [(Char, T.Text)] -> T.Text -> T.Text
-escapeStringUsing tbl = T.concatMap $ \c -> fromMaybe (T.singleton c) $ lookup c tbl
-
 -- | @True@ exactly when the @Char@ appears in the @Text@.
 elemText :: Char -> T.Text -> Bool
 elemText c = T.any (== c)

src/Text/Pandoc/Writers/AsciiDoc.hs

@@ -105,8 +105,11 @@ pandocToAsciiDoc opts (Pandoc meta blocks) = do
 
 -- | Escape special characters for AsciiDoc.
 escapeString :: Text -> Text
-escapeString = escapeStringUsing escs
-  where escs = backslashEscapes "{"
+escapeString t
+  | T.any (== '{') t = T.concatMap escChar t
+  | otherwise        = t
+  where escChar '{' = "\\{"
+        escChar c   = T.singleton c
 
 -- | Ordered list start parser for use in Para below.
 olMarker :: Parser Text ParserState Char
@@ -496,7 +499,9 @@ inlineToAsciiDoc opts (Quoted qt lst) = do
         | otherwise     -> [Str "``"] ++ lst ++ [Str "''"]
 inlineToAsciiDoc _ (Code _ str) = do
   isAsciidoctor <- gets asciidoctorVariant
-  let contents = literal (escapeStringUsing (backslashEscapes "`") str)
+  let escChar '`' = "\\'"
+      escChar c   = T.singleton c
+  let contents = literal (T.concatMap escChar str)
   return $
     if isAsciidoctor
        then text "`+" <> contents <> "+`"

src/Text/Pandoc/Writers/ConTeXt.hs

@@ -434,9 +434,13 @@ inlineToConTeXt (Link _ txt (src, _)) = do
   put $ st {stNextRef = next + 1}
   let ref = "url" <> tshow next
   contents <-  inlineListToConTeXt txt
+  let escChar '#' = "\\#"
+      escChar '%' = "\\%"
+      escChar c   = T.singleton c
+  let escContextURL = T.concatMap escChar
   return $ "\\useURL"
            <> brackets (literal ref)
-           <> brackets (literal $ escapeStringUsing [('#',"\\#"),('%',"\\%")] src)
+           <> brackets (literal $ escContextURL src)
            <> (if isAutolink
                   then empty
                   else brackets empty <> brackets contents)

src/Text/Pandoc/Writers/Haddock.hs

@@ -15,6 +15,7 @@ Haddock:  <http://www.haskell.org/haddock/doc/html/>
 -}
 module Text.Pandoc.Writers.Haddock (writeHaddock) where
 import Control.Monad.State.Strict
+import Data.Char (isAlphaNum)
 import Data.Default
 import Data.Text (Text)
 import qualified Data.Text as T
@@ -71,8 +72,18 @@ notesToHaddock opts notes =
 
 -- | Escape special characters for Haddock.
 escapeString :: Text -> Text
-escapeString = escapeStringUsing haddockEscapes
-  where haddockEscapes = backslashEscapes "\\/'`\"@<"
+escapeString t
+  | T.all isAlphaNum t = t
+  | otherwise = T.concatMap escChar t
+ where
+  escChar '\\' = "\\\\"
+  escChar '/'  = "\\/"
+  escChar '\'' = "\\'"
+  escChar '`'  = "\\`"
+  escChar '"'  = "\\\""
+  escChar '@'  = "\\@"
+  escChar '<'  = "\\<"
+  escChar c    = T.singleton c
 
 -- | Convert Pandoc block element to haddock.
 blockToHaddock :: PandocMonad m

src/Text/Pandoc/Writers/LaTeX.hs

@@ -825,7 +825,19 @@ inlineToLaTeX (Code (_,classes,kvs) str) = do
         let chr = case "!\"'()*,-./:;?@" \\ T.unpack str of
                        (c:_) -> c
                        []    -> '!'
-        let str' = escapeStringUsing (backslashEscapes "\\{}%~_&#^") str
+        let isEscapable '\\' = True
+            isEscapable '{'  = True
+            isEscapable '}'  = True
+            isEscapable '%'  = True
+            isEscapable '~'  = True
+            isEscapable '_'  = True
+            isEscapable '&'  = True
+            isEscapable '#'  = True
+            isEscapable '^'  = True
+            isEscapable _    = False
+        let escChar c | isEscapable c = T.pack ['\\',c]
+                      | otherwise     = T.singleton c
+        let str' = T.concatMap escChar str
         -- we always put lstinline in a dummy 'passthrough' command
         -- (defined in the default template) so that we don't have
         -- to change the way we escape characters depending on whether

src/Text/Pandoc/Writers/Org.hs

@@ -84,12 +84,15 @@ noteToOrg num note = do
 
 -- | Escape special characters for Org.
 escapeString :: Text -> Text
-escapeString = escapeStringUsing
-               [ ('\x2014',"---")
-               , ('\x2013',"--")
-               , ('\x2019',"'")
-               , ('\x2026',"...")
-               ]
+escapeString t
+  | T.all (\c -> c < '\x2013' || c > '\x2026') t = t
+  | otherwise = T.concatMap escChar t
+  where
+   escChar '\x2013' = "--"
+   escChar '\x2014' = "---"
+   escChar '\x2019' = "'"
+   escChar '\x2026' = "..."
+   escChar c        = T.singleton c
 
 isRawFormat :: Format -> Bool
 isRawFormat f =

src/Text/Pandoc/Writers/RTF.hs

@@ -16,7 +16,7 @@ module Text.Pandoc.Writers.RTF ( writeRTF
 import Control.Monad.Except (catchError, throwError)
 import Control.Monad
 import qualified Data.ByteString as B
-import Data.Char (chr, isDigit, ord)
+import Data.Char (chr, isDigit, ord, isAlphaNum)
 import qualified Data.Map as M
 import Data.Text (Text)
 import qualified Data.Text as T
@@ -137,15 +137,21 @@ handleUnicode = T.concatMap $ \c ->
 
 -- | Escape special characters.
 escapeSpecial :: Text -> Text
-escapeSpecial = escapeStringUsing $
-  [ ('\t',"\\tab ")
-  , ('\8216',"\\u8216'")
-  , ('\8217',"\\u8217'")
-  , ('\8220',"\\u8220\"")
-  , ('\8221',"\\u8221\"")
-  , ('\8211',"\\u8211-")
-  , ('\8212',"\\u8212-")
-  ] <> backslashEscapes "{\\}"
+escapeSpecial t
+  | T.all isAlphaNum t = t
+  | otherwise          = T.concatMap escChar t
+ where
+  escChar '\t' = "\\tab "
+  escChar '\8216' = "\\u8216'"
+  escChar '\8217' = "\\u8217'"
+  escChar '\8220' = "\\u8220\""
+  escChar '\8221' = "\\u8221\""
+  escChar '\8211' = "\\u8211-"
+  escChar '\8212' = "\\u8212-"
+  escChar '{'     = "\\{"
+  escChar '}'     = "\\}"
+  escChar '\\'    = "\\\\"
+  escChar c       = T.singleton c
 
 -- | Escape strings as needed for rich text format.
 stringToRTF :: Text -> Text

src/Text/Pandoc/Writers/Texinfo.hs

@@ -14,7 +14,7 @@ Conversion of 'Pandoc' format into Texinfo.
 module Text.Pandoc.Writers.Texinfo ( writeTexinfo ) where
 import Control.Monad.Except (throwError)
 import Control.Monad.State.Strict
-import Data.Char (chr, ord)
+import Data.Char (chr, ord, isAlphaNum)
 import Data.List (maximumBy, transpose, foldl')
 import Data.List.NonEmpty (nonEmpty)
 import Data.Ord (comparing)
@@ -85,16 +85,18 @@ pandocToTexinfo options (Pandoc meta blocks) = do
 
 -- | Escape things as needed for Texinfo.
 stringToTexinfo :: Text -> Text
-stringToTexinfo = escapeStringUsing texinfoEscapes
-  where texinfoEscapes = [ ('{', "@{")
-                         , ('}', "@}")
-                         , ('@', "@@")
-                         , ('\160', "@ ")
-                         , ('\x2014', "---")
-                         , ('\x2013', "--")
-                         , ('\x2026', "@dots{}")
-                         , ('\x2019', "'")
-                         ]
+stringToTexinfo t
+  | T.all isAlphaNum t = t
+  | otherwise = T.concatMap escChar t
+  where escChar '{'      = "@{"
+        escChar '}'      = "@}"
+        escChar '@'      = "@@"
+        escChar '\160'   = "@ "
+        escChar '\x2014' = "---"
+        escChar '\x2013' = "--"
+        escChar '\x2026' = "@dots{}"
+        escChar '\x2019' = "'"
+        escChar c        = T.singleton c
 
 escapeCommas :: PandocMonad m => TI m (Doc Text) -> TI m (Doc Text)
 escapeCommas parser = do