Merge remote-tracking branch 'origin/ghc-8.10' into ghc-9.0

6 files changed, 281 insertions, 85 deletions

diff --git a/haddock-library/src/CompatPrelude.hs b/haddock-library/src/CompatPrelude.hs
new file mode 100644
index 00000000..60fa94d9
--- /dev/null
+++ b/haddock-library/src/CompatPrelude.hs
@@ -0,0 +1,52 @@
+{-# LANGUAGE CPP #-}
+
+#if !MIN_VERSION_base(4,5,0)
+# error This module doesn't provide compat-shims for versions prior to base-4.5
+#endif
+
+-- | Bridge impedance mismatch of different @base@ versions back till @base-4.5@ (GHC 7.4.2)
+module CompatPrelude
+    ( ($>)
+    , isSymbolChar
+    ) where
+
+#if MIN_VERSION_base(4,7,0)
+import           Data.Functor                ( ($>) )
+#else
+import           Data.Functor                ( (<$) )
+#endif
+
+#if MIN_VERSION_base(4,9,0)
+import           Text.Read.Lex                      (isSymbolChar)
+#else
+import           Data.Char (GeneralCategory(..), generalCategory)
+#endif
+
+
+#if !MIN_VERSION_base(4,7,0)
+infixl 4 $>
+
+-- | Flipped version of '<$'.
+--
+-- @since 4.7.0.0
+($>) :: Functor f => f a -> b -> f b
+($>) = flip (<$)
+#endif
+
+#if !MIN_VERSION_base(4,9,0)
+-- inlined from base-4.10.0.0
+isSymbolChar :: Char -> Bool
+isSymbolChar c = not (isPuncChar c) && case generalCategory c of
+    MathSymbol           -> True
+    CurrencySymbol       -> True
+    ModifierSymbol       -> True
+    OtherSymbol          -> True
+    DashPunctuation      -> True
+    OtherPunctuation     -> c `notElem` "'\""
+    ConnectorPunctuation -> c /= '_'
+    _                    -> False
+  where
+    -- | The @special@ character class as defined in the Haskell Report.
+    isPuncChar :: Char -> Bool
+    isPuncChar = (`elem` (",;()[]{}`" :: String))
+#endif
diff --git a/haddock-library/src/Documentation/Haddock/Parser.hs b/haddock-library/src/Documentation/Haddock/Parser.hs
index 82d65a0a..a3bba38a 100644
--- a/haddock-library/src/Documentation/Haddock/Parser.hs
+++ b/haddock-library/src/Documentation/Haddock/Parser.hs
@@ -1,4 +1,3 @@
-{-# LANGUAGE CPP               #-}
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE ViewPatterns      #-}
 -- |
@@ -27,7 +26,7 @@ module Documentation.Haddock.Parser (
 import           Control.Applicative
 import           Control.Arrow (first)
 import           Control.Monad
-import           Data.Char (chr, isUpper, isAlpha, isAlphaNum, isSpace)
+import           Data.Char (chr, isUpper, isAlpha, isSpace)
 import           Data.List (intercalate, unfoldr, elemIndex)
 import           Data.Maybe (fromMaybe, mapMaybe)
 import           Data.Monoid
@@ -36,6 +35,7 @@ import           Documentation.Haddock.Doc
 import           Documentation.Haddock.Markup ( markup, plainMarkup )
 import           Documentation.Haddock.Parser.Monad
 import           Documentation.Haddock.Parser.Util
+import           Documentation.Haddock.Parser.Identifier
 import           Documentation.Haddock.Types
 import           Prelude hiding (takeWhile)
 import qualified Prelude as P
@@ -46,53 +46,26 @@ import           Text.Parsec (try)
 import qualified Data.Text as T
 import           Data.Text (Text)
 
-#if MIN_VERSION_base(4,9,0)
-import           Text.Read.Lex                      (isSymbolChar)
-#else
-import           Data.Char                          (GeneralCategory (..),
-                                                     generalCategory)
-#endif
 
 -- $setup
 -- >>> :set -XOverloadedStrings
 
-#if !MIN_VERSION_base(4,9,0)
--- inlined from base-4.10.0.0
-isSymbolChar :: Char -> Bool
-isSymbolChar c = not (isPuncChar c) && case generalCategory c of
-    MathSymbol           -> True
-    CurrencySymbol       -> True
-    ModifierSymbol       -> True
-    OtherSymbol          -> True
-    DashPunctuation      -> True
-    OtherPunctuation     -> c `notElem` ("'\"" :: String)
-    ConnectorPunctuation -> c /= '_'
-    _                    -> False
-  where
-    -- | The @special@ character class as defined in the Haskell Report.
-    isPuncChar :: Char -> Bool
-    isPuncChar = (`elem` (",;()[]{}`" :: String))
-#endif
-
--- | Identifier string surrounded with opening and closing quotes/backticks.
-type Identifier = (Char, String, Char)
-
 -- | Drops the quotes/backticks around all identifiers, as if they
 -- were valid but still 'String's.
 toRegular :: DocH mod Identifier -> DocH mod String
-toRegular = fmap (\(_, x, _) -> x)
+toRegular = fmap (\(Identifier _ _ x _) -> x)
 
 -- | Maps over 'DocIdentifier's over 'String' with potentially failing
 -- conversion using user-supplied function. If the conversion fails,
 -- the identifier is deemed to not be valid and is treated as a
 -- regular string.
-overIdentifier :: (String -> Maybe a)
+overIdentifier :: (Namespace -> String -> Maybe a)
                -> DocH mod Identifier
                -> DocH mod a
 overIdentifier f d = g d
   where
-    g (DocIdentifier (o, x, e)) = case f x of
-      Nothing -> DocString $ o : x ++ [e]
+    g (DocIdentifier (Identifier ns o x e)) = case f ns x of
+      Nothing -> DocString $ renderNs ns ++ [o] ++ x ++ [e]
       Just x' -> DocIdentifier x'
     g DocEmpty = DocEmpty
     g (DocAppend x x') = DocAppend (g x) (g x')
@@ -254,7 +227,7 @@ takeWhile1_ = mfilter (not . T.null) . takeWhile_
 -- DocAName "Hello world"
 anchor :: Parser (DocH mod a)
 anchor = DocAName . T.unpack <$>
-         disallowNewline ("#" *> takeWhile1_ (/= '#') <* "#")
+         ("#" *> takeWhile1_ (\x -> x /= '#' && not (isSpace x)) <* "#")
 
 -- | Monospaced strings.
 --
@@ -269,12 +242,18 @@ monospace = DocMonospaced . parseParagraph
 -- Note that we allow '#' and '\' to support anchors (old style anchors are of
 -- the form "SomeModule\#anchor").
 moduleName :: Parser (DocH mod a)
-moduleName = DocModule <$> ("\"" *> modid <* "\"")
+moduleName = DocModule <$> ("\"" *> (modid `maybeFollowedBy` anchor_) <* "\"")
   where
     modid = intercalate "." <$> conid `Parsec.sepBy1` "."
+    anchor_ = (++)
+      <$> (Parsec.string "#" <|> Parsec.string "\\#")
+      <*> many (Parsec.satisfy (\c -> c /= '"' && not (isSpace c)))
+
+    maybeFollowedBy pre suf = (\x -> maybe x (x ++)) <$> pre <*> optional suf
+
     conid = (:)
       <$> Parsec.satisfy (\c -> isAlpha c && isUpper c)
-      <*> many (conChar <|> Parsec.oneOf "\\#")
+      <*> many conChar
 
     conChar = Parsec.alphaNum <|> Parsec.char '_'
 
@@ -294,7 +273,7 @@ picture = DocPic . makeLabeled Picture
 -- >>> parseString "\\(\\int_{-\\infty}^{\\infty} e^{-x^2/2} = \\sqrt{2\\pi}\\)"
 -- DocMathInline "\\int_{-\\infty}^{\\infty} e^{-x^2/2} = \\sqrt{2\\pi}"
 mathInline :: Parser (DocH mod a)
-mathInline = DocMathInline . T.unpack 
+mathInline = DocMathInline . T.unpack
              <$> disallowNewline  ("\\(" *> takeUntil "\\)")
 
 -- | Display math parser, surrounded by \\[ and \\].
@@ -314,7 +293,8 @@ markdownImage :: Parser (DocH mod Identifier)
 markdownImage = DocPic . fromHyperlink <$> ("!" *> linkParser)
   where
     fromHyperlink (Hyperlink u l) = Picture u (fmap (markup stringMarkup) l)
-    stringMarkup = plainMarkup (const "") (\(l,c,r) -> [l] <> c <> [r])
+    stringMarkup = plainMarkup (const "") renderIdent
+    renderIdent (Identifier ns l c r) = renderNs ns <> [l] <> c <> [r]
 
 -- | Paragraph parser, called by 'parseParas'.
 paragraph :: Parser (DocH mod Identifier)
@@ -518,7 +498,7 @@ tableStepFour rs hdrIndex cells =  case hdrIndex of
     -- extract cell contents given boundaries
     extract :: Int -> Int -> Int -> Int -> Text
     extract x y x2 y2 = T.intercalate "\n"
-        [ T.take (x2 - x + 1) $ T.drop x $ rs !! y'
+        [ T.stripEnd $ T.stripStart $ T.take (x2 - x + 1) $ T.drop x $ rs !! y'
         | y' <- [y .. y2]
         ]
 
@@ -538,11 +518,11 @@ since = ("@since " *> version <* skipHorizontalSpace <* endOfLine) >>= setSince
 header :: Parser (DocH mod Identifier)
 header = do
   let psers = map (string . flip T.replicate "=") [6, 5 .. 1]
-      pser = choice' psers
-  delim <- T.unpack <$> pser
-  line <- skipHorizontalSpace *> nonEmptyLine >>= return . parseText
+      pser = Parsec.choice psers
+  depth <- T.length <$> pser
+  line <- parseText <$> (skipHorizontalSpace *> nonEmptyLine)
   rest <- try paragraph <|> return DocEmpty
-  return $ DocHeader (Header (length delim) line) `docAppend` rest
+  return $ DocHeader (Header depth line) `docAppend` rest
 
 textParagraph :: Parser (DocH mod Identifier)
 textParagraph = parseText . T.intercalate "\n" <$> some nonEmptyLine
@@ -605,7 +585,7 @@ definitionList indent = DocDefList <$> p
         Right i -> (label, contents) : i
 
 -- | Drops all trailing newlines.
-dropNLs :: Text -> Text 
+dropNLs :: Text -> Text
 dropNLs = T.dropWhileEnd (== '\n')
 
 -- | Main worker for 'innerList' and 'definitionList'.
@@ -679,7 +659,7 @@ takeNonEmptyLine = do
 --
 -- More precisely: skips all whitespace-only lines and returns indentation
 -- (horizontal space, might be empty) of that non-empty line.
-takeIndent :: Parser Text 
+takeIndent :: Parser Text
 takeIndent = do
   indent <- takeHorizontalSpace
   choice' [ "\n" *> takeIndent
@@ -737,14 +717,14 @@ examples = DocExamples <$> (many (try (skipHorizontalSpace *> "\n")) *> go)
         substituteBlankLine "<BLANKLINE>" = ""
         substituteBlankLine xs = xs
 
-nonEmptyLine :: Parser Text 
+nonEmptyLine :: Parser Text
 nonEmptyLine = try (mfilter (T.any (not . isSpace)) takeLine)
 
 takeLine :: Parser Text
 takeLine = try (takeWhile (/= '\n') <* endOfLine)
 
 endOfLine :: Parser ()
-endOfLine = void "\n" <|> Parsec.eof 
+endOfLine = void "\n" <|> Parsec.eof
 
 -- | Property parser.
 --
@@ -826,7 +806,7 @@ autoUrl :: Parser (DocH mod a)
 autoUrl = mkLink <$> url
   where
     url = mappend <$> choice' [ "http://", "https://", "ftp://"] <*> takeWhile1 (not . isSpace)
-    
+
     mkLink :: Text -> DocH mod a
     mkLink s = case T.unsnoc s of
       Just (xs,x) | x `elem` (",.!?" :: String) -> DocHyperlink (mkHyperlink xs) `docAppend` DocString [x]
@@ -836,30 +816,6 @@ autoUrl = mkLink <$> url
     mkHyperlink lnk = Hyperlink (T.unpack lnk) Nothing
 
 
-
--- | Parses strings between identifier delimiters. Consumes all input that it
--- deems to be valid in an identifier. Note that it simply blindly consumes
--- characters and does no actual validation itself.
-parseValid :: Parser String
-parseValid = p some
-  where
-    idChar = Parsec.satisfy (\c -> isAlphaNum c || isSymbolChar c || c == '_')
-
-    p p' = do
-      vs <- p' idChar
-      c <- peekChar'
-      case c of
-        '`' -> return vs
-        '\'' -> choice' [ (\x -> vs ++ "'" ++ x) <$> ("'" *> p many), return vs ]
-        _ -> fail "outofvalid"
-
--- | Parses identifiers with help of 'parseValid'. Asks GHC for
--- 'String' from the string it deems valid.
+-- | Parses identifiers with help of 'parseValid'.
 identifier :: Parser (DocH mod Identifier)
-identifier = do
-  o <- idDelim
-  vid <- parseValid
-  e <- idDelim
-  return $ DocIdentifier (o, vid, e)
-  where
-    idDelim = Parsec.satisfy (\c -> c == '\'' || c == '`')
+identifier = DocIdentifier <$> parseValid
diff --git a/haddock-library/src/Documentation/Haddock/Parser/Identifier.hs b/haddock-library/src/Documentation/Haddock/Parser/Identifier.hs
new file mode 100644
index 00000000..b8afb951
--- /dev/null
+++ b/haddock-library/src/Documentation/Haddock/Parser/Identifier.hs
@@ -0,0 +1,160 @@
+{-# LANGUAGE BangPatterns #-}
+{-# LANGUAGE ViewPatterns #-}
+-- |
+-- Module      :  Documentation.Haddock.Parser.Identifier
+-- Copyright   :  (c) Alec Theriault 2019,
+-- License     :  BSD-like
+--
+-- Maintainer  :  haddock@projects.haskell.org
+-- Stability   :  experimental
+-- Portability :  portable
+--
+-- Functionality for parsing identifiers and operators
+
+module Documentation.Haddock.Parser.Identifier (
+  Identifier(..),
+  parseValid,
+) where
+
+import Documentation.Haddock.Types           ( Namespace(..) )
+import Documentation.Haddock.Parser.Monad
+import qualified Text.Parsec as Parsec
+import           Text.Parsec.Pos             ( updatePosChar )
+import           Text.Parsec                 ( State(..)
+                                             , getParserState, setParserState )
+
+import Data.Text (Text)
+import qualified Data.Text as T
+
+import           Data.Char (isAlpha, isAlphaNum)
+import Control.Monad (guard)
+import Data.Maybe
+import CompatPrelude
+
+-- | Identifier string surrounded with namespace, opening, and closing quotes/backticks.
+data Identifier = Identifier !Namespace !Char String !Char
+  deriving (Show, Eq)
+
+parseValid :: Parser Identifier
+parseValid = do
+  s@State{ stateInput = inp, statePos = pos } <- getParserState
+
+  case takeIdentifier inp of
+    Nothing -> Parsec.parserFail "parseValid: Failed to match a valid identifier"
+    Just (ns, op, ident, cl, inp') ->
+      let posOp = updatePosChar pos op
+          posIdent = T.foldl updatePosChar posOp ident
+          posCl = updatePosChar posIdent cl
+          s' = s{ stateInput = inp', statePos = posCl }
+      in setParserState s' $> Identifier ns op (T.unpack ident) cl
+
+
+-- | Try to parse a delimited identifier off the front of the given input.
+--
+-- This tries to match as many valid Haskell identifiers/operators as possible,
+-- to the point of sometimes accepting invalid things (ex: keywords). Some
+-- considerations:
+--
+--   - operators and identifiers can have module qualifications
+--   - operators can be wrapped in parens (for prefix)
+--   - identifiers can be wrapped in backticks (for infix)
+--   - delimiters are backticks or regular ticks
+--   - since regular ticks are also valid in identifiers, we opt for the
+--     longest successful parse
+--
+-- This function should make /O(1)/ allocations
+takeIdentifier :: Text -> Maybe (Namespace, Char, Text, Char, Text)
+takeIdentifier input = listToMaybe $ do
+
+    -- Optional namespace
+    let (ns, input') = case T.uncons input of
+                         Just ('v', i) -> (Value, i)
+                         Just ('t', i) -> (Type, i)
+                         _             -> (None, input)
+
+    -- Opening tick
+    (op, input'') <- maybeToList (T.uncons input')
+    guard (op == '\'' || op == '`')
+
+    -- Identifier/operator
+    (ident, input''') <- wrapped input''
+
+    -- Closing tick
+    (cl, input'''') <- maybeToList (T.uncons input''')
+    guard (cl == '\'' || cl == '`')
+
+    return (ns, op, ident, cl, input'''')
+
+  where
+
+    -- | Parse out a wrapped, possibly qualified, operator or identifier
+    wrapped t = do
+      (c, t'  ) <- maybeToList (T.uncons t)
+      -- Tuples
+      case c of
+        '(' | Just (c', _) <- T.uncons t'
+            , c' == ',' || c' == ')'
+            -> do let (commas, t'') = T.span (== ',') t'
+                  (')', t''') <- maybeToList (T.uncons t'')
+                  return (T.take (T.length commas + 2) t, t''')
+
+        -- Parenthesized
+        '(' -> do (n,   t'' ) <- general False 0 [] t'
+                  (')', t''') <- maybeToList (T.uncons t'')
+                  return (T.take (n + 2) t, t''')
+
+        -- Backticked
+        '`' -> do (n,   t'' ) <- general False 0 [] t'
+                  ('`', t''') <- maybeToList (T.uncons t'')
+                  return (T.take (n + 2) t, t''')
+
+        -- Unadorned
+        _   -> do (n,   t'' ) <- general False 0 [] t
+                  return (T.take n t, t'')
+
+    -- | Parse out a possibly qualified operator or identifier
+    general :: Bool           -- ^ refuse inputs starting with operators
+            -> Int            -- ^ total characters \"consumed\" so far
+            -> [(Int, Text)]  -- ^ accumulated results
+            -> Text           -- ^ current input
+            -> [(Int, Text)]  -- ^ total characters parsed & what remains
+    general !identOnly !i acc t
+      -- Starts with an identifier (either just an identifier, or a module qual)
+      | Just (n, rest) <- identLike t
+      = if T.null rest
+          then acc
+          else case T.head rest of
+                 '`' -> (n + i, rest) : acc
+                 ')' -> (n + i, rest) : acc
+                 '.' -> general False (n + i + 1) acc (T.tail rest)
+                 '\'' -> let (m, rest') = quotes rest
+                         in general True (n + m + 1 + i) ((n + m + i, rest') : acc) (T.tail rest')
+                 _ -> acc
+
+      -- An operator
+      | Just (n, rest) <- optr t
+      , not identOnly
+      = (n + i, rest) : acc
+
+      -- Anything else
+      | otherwise
+      = acc
+
+    -- | Parse an identifier off the front of the input
+    identLike t
+      | T.null t = Nothing
+      | isAlpha (T.head t) || '_' == T.head t
+      = let !(idt, rest) = T.span (\c -> isAlphaNum c || c == '_') t
+            !(octos, rest') = T.span (== '#') rest
+      in Just (T.length idt + T.length octos, rest')
+      | otherwise = Nothing
+
+    -- | Parse all but the last quote off the front of the input
+    -- PRECONDITION: T.head t == '\''
+    quotes :: Text -> (Int, Text)
+    quotes t = let !n = T.length (T.takeWhile (== '\'') t) - 1
+               in (n, T.drop n t)
+
+    -- | Parse an operator off the front of the input
+    optr t = let !(op, rest) = T.span isSymbolChar t
+             in if T.null op then Nothing else Just (T.length op, rest)
diff --git a/haddock-library/src/Documentation/Haddock/Parser/Monad.hs b/haddock-library/src/Documentation/Haddock/Parser/Monad.hs
index 8f5bd217..7c73a168 100644
--- a/haddock-library/src/Documentation/Haddock/Parser/Monad.hs
+++ b/haddock-library/src/Documentation/Haddock/Parser/Monad.hs
@@ -4,6 +4,18 @@
 {-# LANGUAGE TypeFamilies #-}
 {-# LANGUAGE BangPatterns #-}
 {-# LANGUAGE TypeSynonymInstances #-}
+-- |
+-- Module      :  Documentation.Haddock.Parser.Monad
+-- Copyright   :  (c) Alec Theriault 2018-2019,
+-- License     :  BSD-like
+--
+-- Maintainer  :  haddock@projects.haskell.org
+-- Stability   :  experimental
+-- Portability :  portable
+--
+-- Defines the Parsec monad over which all parsing is done and also provides
+-- more efficient versions of the usual parsec combinator functions (but
+-- specialized to 'Text').
 
 module Documentation.Haddock.Parser.Monad where
 
@@ -17,7 +29,6 @@ import qualified Data.Text as T
 import           Data.Text                   ( Text )
 
 import           Control.Monad               ( mfilter )
-import           Data.Functor                ( ($>) )
 import           Data.String                 ( IsString(..) )
 import           Data.Bits                   ( Bits(..) )
 import           Data.Char                   ( ord )
@@ -25,7 +36,9 @@ import           Data.List                   ( foldl' )
 import           Control.Applicative as App
 
 import           Documentation.Haddock.Types ( Version )
+
 import           Prelude hiding (takeWhile)
+import           CompatPrelude
 
 -- | The only bit of information we really care about truding along with us
 -- through parsing is the version attached to a @\@since@ annotation - if
@@ -96,7 +109,6 @@ takeWhile f = do
       s' = s{ stateInput = inp', statePos = pos' }
   setParserState s' $> t
 
-
 -- | Like 'takeWhile', but fails if no characters matched.
 --
 -- Equivalent to @fmap T.pack . Parsec.many1@, but more efficient.
diff --git a/haddock-library/src/Documentation/Haddock/Parser/Util.hs b/haddock-library/src/Documentation/Haddock/Parser/Util.hs
index 98570c22..eef744d8 100644
--- a/haddock-library/src/Documentation/Haddock/Parser/Util.hs
+++ b/haddock-library/src/Documentation/Haddock/Parser/Util.hs
@@ -31,16 +31,16 @@ import           Prelude hiding (takeWhile)
 import           Data.Char (isSpace)
 
 -- | Characters that count as horizontal space
-horizontalSpace :: [Char]
-horizontalSpace = " \t\f\v\r"
+horizontalSpace :: Char -> Bool
+horizontalSpace c = isSpace c && c /= '\n'
 
 -- | Skip and ignore leading horizontal space
 skipHorizontalSpace :: Parser ()
-skipHorizontalSpace = Parsec.skipMany (Parsec.oneOf horizontalSpace)
+skipHorizontalSpace = Parsec.skipMany (Parsec.satisfy horizontalSpace)
 
 -- | Take leading horizontal space
-takeHorizontalSpace :: Parser Text 
-takeHorizontalSpace = takeWhile (`elem` horizontalSpace)
+takeHorizontalSpace :: Parser Text
+takeHorizontalSpace = takeWhile horizontalSpace
 
 makeLabeled :: (String -> Maybe String -> a) -> Text -> a
 makeLabeled f input = case T.break isSpace $ removeEscapes $ T.strip input of
@@ -60,10 +60,10 @@ removeEscapes = T.unfoldr go
 
 -- | Consume characters from the input up to and including the given pattern.
 -- Return everything consumed except for the end pattern itself.
-takeUntil :: Text -> Parser Text 
+takeUntil :: Text -> Parser Text
 takeUntil end_ = T.dropEnd (T.length end_) <$> requireEnd (scan p (False, end)) >>= gotSome
   where
-    end = T.unpack end_ 
+    end = T.unpack end_
 
     p :: (Bool, String) -> Char -> Maybe (Bool, String)
     p acc c = case acc of
diff --git a/haddock-library/src/Documentation/Haddock/Types.hs b/haddock-library/src/Documentation/Haddock/Types.hs
index f8f7d353..12ccd28d 100644
--- a/haddock-library/src/Documentation/Haddock/Types.hs
+++ b/haddock-library/src/Documentation/Haddock/Types.hs
@@ -44,14 +44,17 @@ data MetaDoc mod id =
           } deriving (Eq, Show, Functor, Foldable, Traversable)
 
 #if MIN_VERSION_base(4,8,0)
+-- | __NOTE__: Only defined for @base >= 4.8.0@
 instance Bifunctor MetaDoc where
   bimap f g (MetaDoc m d) = MetaDoc m (bimap f g d)
 #endif
 
 #if MIN_VERSION_base(4,10,0)
+-- | __NOTE__: Only defined for @base >= 4.10.0@
 instance Bifoldable MetaDoc where
   bifoldr f g z d = bifoldr f g z (_doc d)
 
+-- | __NOTE__: Only defined for @base >= 4.10.0@
 instance Bitraversable MetaDoc where
   bitraverse f g (MetaDoc m d) = MetaDoc m <$> bitraverse f g d
 #endif
@@ -76,7 +79,7 @@ data Picture = Picture
   } deriving (Eq, Show)
 
 data Header id = Header
-  { headerLevel :: Int
+  { headerLevel :: Int  -- ^ between 1 and 6 inclusive
   , headerTitle :: id
   } deriving (Eq, Show, Functor, Foldable, Traversable)
 
@@ -123,7 +126,7 @@ data DocH mod id
   | DocMathInline String
   | DocMathDisplay String
   | DocAName String
-  -- ^ A (HTML) anchor.
+  -- ^ A (HTML) anchor. It must not contain any spaces.
   | DocProperty String
   | DocExamples [Example]
   | DocHeader (Header (DocH mod id))
@@ -131,6 +134,7 @@ data DocH mod id
   deriving (Eq, Show, Functor, Foldable, Traversable)
 
 #if MIN_VERSION_base(4,8,0)
+-- | __NOTE__: Only defined for @base >= 4.8.0@
 instance Bifunctor DocH where
   bimap _ _ DocEmpty = DocEmpty
   bimap f g (DocAppend docA docB) = DocAppend (bimap f g docA) (bimap f g docB)
@@ -159,6 +163,7 @@ instance Bifunctor DocH where
 #endif
 
 #if MIN_VERSION_base(4,10,0)
+-- | __NOTE__: Only defined for @base >= 4.10.0@
 instance Bifoldable DocH where
   bifoldr f g z (DocAppend docA docB) = bifoldr f g (bifoldr f g z docA) docB
   bifoldr f g z (DocParagraph doc) = bifoldr f g z doc
@@ -176,6 +181,7 @@ instance Bifoldable DocH where
   bifoldr f g z (DocTable (Table header body)) = foldr (\r acc -> foldr (flip (bifoldr f g)) acc r) (foldr (\r acc -> foldr (flip (bifoldr f g)) acc r) z body) header
   bifoldr _ _ z _ = z
 
+-- | __NOTE__: Only defined for @base >= 4.10.0@
 instance Bitraversable DocH where
   bitraverse _ _ DocEmpty = pure DocEmpty
   bitraverse f g (DocAppend docA docB) = DocAppend <$> bitraverse f g docA <*> bitraverse f g docB
@@ -203,6 +209,16 @@ instance Bitraversable DocH where
   bitraverse f g (DocTable (Table header body)) = (\h b -> DocTable (Table h b)) <$> traverse (traverse (bitraverse f g)) header <*> traverse (traverse (bitraverse f g)) body
 #endif
 
+-- | The namespace qualification for an identifier.
+data Namespace = Value | Type | None deriving (Eq, Ord, Enum, Show)
+
+-- | Render the a namespace into the same format it was initially parsed.
+renderNs :: Namespace -> String
+renderNs Value = "v"
+renderNs Type = "t"
+renderNs None = ""
+
+
 -- | 'DocMarkupH' is a set of instructions for marking up documentation.
 -- In fact, it's really just a mapping from 'Doc' to some other
 -- type [a], where [a] is usually the type of the output (HTML, say).