Internal.hs

{-# LANGUAGE Rank2Types, RecordWildCards #-}
-- |
-- Module      :  Data.Attoparsec.Text.Internal
-- Copyright   :  Felipe Lessa 2010, Bryan O'Sullivan 2007-2010
-- License     :  BSD3
--
-- Maintainer  :  felipe.lessa@gmail.com
-- Stability   :  experimental
-- Portability :  unknown
--
-- Simple, efficient parser combinators for 'T.Text' strings,
-- loosely based on the Parsec library, heavily based on attoparsec.

module Data.Attoparsec.Text.Internal
    (
    -- * Parser types
      Parser
    , Result(..)
    , S(input)

    -- * Running parsers
    , parse

    -- * Combinators
    , (<?>)
    , try
    , module Data.Attoparsec.Combinator

    -- * Parsing individual characters
    , satisfy
    , satisfyWith
    , anyChar
    , skip
    , char
    , notChar

    -- ** Character classes
    , inClass
    , notInClass

    -- * Efficient string handling
    , skipWhile
    , string
    , stringTransform
    , take
    , takeWhile
    , takeWhile1
    , takeTill

    -- * State observation and manipulation functions
    , endOfInput
    , ensure

    -- * Utilities
    , endOfLine
    ) where

import Control.Applicative (Alternative(..), Applicative(..), (<$>))
import Control.Monad (MonadPlus(..), when)
import Data.Attoparsec.Combinator
import Data.Attoparsec.Text.FastSet (charClass, member)
import Data.Monoid (Monoid(..))
import Prelude hiding (getChar, take, takeWhile)
import qualified Data.Text as T

data Result r = Fail S [String] String
              | Partial (T.Text -> Result r)
              | Done S r

-- | The 'Parser' type is a monad.
newtype Parser a = Parser {
      runParser :: forall r. S
                -> Failure   r
                -> Success a r
                -> Result r
    }

type Failure   r = S -> [String] -> String -> Result r
type Success a r = S -> a -> Result r

-- | Have we read all available input?
data More = Complete | Incomplete
            deriving (Eq, Show)

plusMore :: More -> More -> More
plusMore Complete _ = Complete
plusMore _ Complete = Complete
plusMore _ _        = Incomplete
{-# INLINE plusMore #-}

instance Monoid More where
    mempty  = Incomplete
    mappend = plusMore

data S = S {
      input  :: !T.Text
    , _added :: !T.Text
    , more  :: !More
    } deriving (Show)

instance Show r => Show (Result r) where
    show (Fail _ stack msg) = "Fail " ++ show stack ++ " " ++ show msg
    show (Partial _) = "Partial _"
    show (Done bs r) = "Done " ++ show bs ++ " " ++ show r

addS :: S -> S -> S
addS (S s0 a0 c0) (S _s1 a1 c1) = S (s0 +++ a1) (a0 +++ a1) (mappend c0 c1)
{-# INLINE addS #-}

instance Monoid S where
    mempty  = S T.empty T.empty Incomplete
    mappend = addS

bindP :: Parser a -> (a -> Parser b) -> Parser b
bindP m g =
    Parser (\st0 kf ks -> runParser m st0 kf (\s a -> runParser (g a) s kf ks))
{-# INLINE bindP #-}

returnP :: a -> Parser a
returnP a = Parser (\st0 _kf ks -> ks st0 a)
{-# INLINE returnP #-}

instance Monad Parser where
    return = returnP
    (>>=)  = bindP
    fail   = failDesc

noAdds :: S -> S
noAdds (S s0 _a0 c0) = S s0 T.empty c0
{-# INLINE noAdds #-}

plus :: Parser a -> Parser a -> Parser a
plus a b = Parser $ \st0 kf ks ->
           let kf' st1 _ _ = runParser b (mappend st0 st1) kf ks
               !st2 = noAdds st0
           in  runParser a st2 kf' ks
{-# INLINE plus #-}

instance MonadPlus Parser where
    mzero = failDesc "mzero"
    mplus = plus

fmapP :: (a -> b) -> Parser a -> Parser b
fmapP p m = Parser (\st0 f k -> runParser m st0 f (\s a -> k s (p a)))
{-# INLINE fmapP #-}

instance Functor Parser where
    fmap = fmapP

apP :: Parser (a -> b) -> Parser a -> Parser b
apP d e = do
  b <- d
  a <- e
  return (b a)
{-# INLINE apP #-}

instance Applicative Parser where
    pure   = returnP
    (<*>)  = apP

    -- These definitions are equal to the defaults, but this
    -- way the optimizer doesn't have to work so hard to figure
    -- that out.
    (*>)   = (>>)
    x <* y = x >>= \a -> y >> return a

instance Alternative Parser where
    empty = failDesc "empty"
    (<|>) = plus

failDesc :: String -> Parser a
failDesc err = Parser (\st0 kf _ks -> kf st0 [] msg)
    where msg = "Failed reading: " ++ err
{-# INLINE failDesc #-}

-- | Succeed only if at least @n@ characters of input are available.
ensure :: Int -> Parser ()
ensure n = Parser $ \st0@(S s0 _a0 _c0) kf ks ->
    if T.length s0 >= n
    then ks st0 ()
    else runParser (demandInput >> ensure n) st0 kf ks

-- | Ask for input.  If we receive any, pass it to a success
-- continuation, otherwise to a failure continuation.
prompt :: S -> (S -> Result r) -> (S -> Result r) -> Result r
prompt (S s0 a0 _c0) kf ks = Partial $ \s ->
    if T.null s
    then kf $! S s0 a0 Complete
    else ks $! S (s0 +++ s) (a0 +++ s) Incomplete

-- | Immediately demand more input via a 'Partial' continuation
-- result.
demandInput :: Parser ()
demandInput = Parser $ \st0 kf ks ->
    if more st0 == Complete
    then kf st0 ["demandInput"] "not enough characters"
    else prompt st0 (\st -> kf st ["demandInput"] "not enough characters") (`ks` ())

-- | This parser always succeeds.  It returns 'True' if any input is
-- available either immediately or on demand, and 'False' if the end
-- of all input has been reached.
wantInput :: Parser Bool
wantInput = Parser $ \st0@(S s0 _a0 c0) _kf ks ->
  case () of
    _ | not (T.null s0) -> ks st0 True
      | c0 == Complete  -> ks st0 False
      | otherwise       -> prompt st0 (`ks` False) (`ks` True)

get :: Parser T.Text
get  = Parser (\st0 _kf ks -> ks st0 (input st0))

put :: T.Text -> Parser ()
put s = Parser (\(S _s0 a0 c0) _kf ks -> ks (S s a0 c0) ())

(+++) :: T.Text -> T.Text -> T.Text
(+++) = T.append
{-# INLINE (+++) #-}

-- | Attempt a parse, and if it fails, rewind the input so that no
-- input appears to have been consumed.
--
-- This combinator is useful in cases where a parser might consume
-- some input before failing, i.e. the parser needs arbitrary
-- lookahead.  The downside to using this combinator is that it can
-- retain input for longer than is desirable.
try :: Parser a -> Parser a
try p = Parser $ \st0 kf ks ->
        runParser p (noAdds st0) (kf . mappend st0) ks

-- | The parser @satisfy p@ succeeds for any character for which
-- the predicate @p@ returns 'True'. Returns the character that
-- is actually parsed.
--
-- >import Data.Char (isDigit)
-- >digit = satisfy isDigit
satisfy :: (Char -> Bool) -> Parser Char
satisfy p = do
  ensure 1
  s <- get
  case T.uncons s of
    Just (h,t) | p h       -> put t >> return h
               | otherwise -> fail "satisfy"

-- | The parser @skip p@ succeeds for any character for which the
-- predicate @p@ returns 'True'.
--
-- >import Data.Char (isDigit)
-- >digit = satisfy isDigit
skip :: (Char -> Bool) -> Parser ()
skip p = do
  ensure 1
  s <- get
  case T.uncons s of
    Just (h,t) | p h       -> put t
               | otherwise -> fail "skip"


-- | The parser @satisfyWith f p@ transforms a character, and
-- succeeds if the predicate @p@ returns 'True' on the
-- transformed value. The parser returns the transformed
-- character that was parsed.
satisfyWith :: (Char -> a) -> (a -> Bool) -> Parser a
satisfyWith f p = do
  ensure 1
  s <- get
  let Just (h,t) = T.uncons s
      c = f h
  if p c
    then put t >> return c
    else fail "satisfyWith"

-- | Consume @n@ characters of input, but succeed only if the
-- predicate returns 'True'.
takeWith :: Int -> (T.Text -> Bool) -> Parser T.Text
takeWith n p = do
  ensure n
  s <- get
  let (h,t) = T.splitAt n s
  if p h
    then put t >> return h
    else failDesc "takeWith"

-- | Consume exactly @n@ characters of input.
take :: Int -> Parser T.Text
take n = takeWith n (const True)
{-# INLINE take #-}

-- | @string s@ parses a sequence of characters that identically
-- match @s@. Returns the parsed string (i.e. @s@).  This parser
-- consumes no input if it fails (even if a partial match).
--
-- /Note/: The behaviour of this parser is different to that of the
-- similarly-named parser in Parsec, as this one is all-or-nothing.
-- To illustrate the difference, the following parser will fail under
-- Parsec given an input of @"for"@:
--
-- >string "foo" <|> string "for"
--
-- The reason for its failure is that that the first branch is a
-- partial match, and will consume the letters @\'f\'@ and
-- @\'o\'@ before failing.  In Attoparsec, both the original on
-- bytestrings and this one on texts, the above parser will
-- /succeed/ on that input, because the failed first branch will
-- consume nothing.
string :: T.Text -> Parser T.Text
string s = takeWith (T.length s) (==s)
{-# INLINE string #-}

stringTransform :: (T.Text -> T.Text) -> T.Text
                -> Parser T.Text
stringTransform f s = takeWith (T.length s) ((==f s) . f)
{-# INLINE stringTransform #-}

-- | Skip past input for as long as the predicate returns 'True'.
skipWhile :: (Char -> Bool) -> Parser ()
skipWhile p = go
 where
  go = do
    input <- wantInput
    when input $ do
      t <- T.dropWhile p <$> get
      put t
      when (T.null t) go

-- | Consume input as long as the predicate returns 'False'
-- (i.e. until it returns 'True'), and return the consumed input.
--
-- This parser does not fail.  It will return an empty string if the
-- predicate returns 'True' on the first character of input.
--
-- /Note/: Because this parser does not fail, do not use it with
-- combinators such as 'many', because such parsers loop until a
-- failure occurs.  Careless use will thus result in an infinite loop.
takeTill :: (Char -> Bool) -> Parser T.Text
takeTill p = takeWhile (not . p)
{-# INLINE takeTill #-}

-- | Consume input as long as the predicate returns 'True', and return
-- the consumed input.
--
-- This parser does not fail.  It will return an empty string if the
-- predicate returns 'False' on the first character of input.
--
-- /Note/: Because this parser does not fail, do not use it with
-- combinators such as 'many', because such parsers loop until a
-- failure occurs.  Careless use will thus result in an infinite loop.
takeWhile :: (Char -> Bool) -> Parser T.Text
takeWhile p = go []
 where
  go acc = do
    input <- wantInput
    if input
      then do
#if MIN_VERSION_text(0,11,0)
        (h,t) <- T.span p <$> get
#else
        (h,t) <- T.spanBy p <$> get
#endif
        put t
        if T.null t
          then go (h:acc)
          else return $ if null acc then h else T.concat $ reverse (h:acc)
      else return $ case acc of
                      []  -> T.empty
                      [x] -> x
                      _   -> T.concat $ reverse acc

-- | Consume input as long as the predicate returns 'True', and return
-- the consumed input.
--
-- This parser requires the predicate to succeed on at least one
-- character of input: it will fail if the predicate never
-- returns 'True' or if there is no input left.
takeWhile1 :: (Char -> Bool) -> Parser T.Text
takeWhile1 p = do
  (`when` demandInput) =<< T.null <$> get
#if MIN_VERSION_text(0,11,0)
  (h,t) <- T.span p <$> get
#else
  (h,t) <- T.spanBy p <$> get
#endif
  when (T.null h) $ failDesc "takeWhile1"
  put t
  if T.null t
    then (h+++) `fmapP` takeWhile p
    else return h

-- | Match any character in a set.
--
-- >vowel = inClass "aeiou"
--
-- Range notation is supported.
--
-- >halfAlphabet = inClass "a-nA-N"
--
-- To add a literal @\'-\'@ to a set, place it at the beginning or end
-- of the string.
inClass :: String -> Char -> Bool
inClass s = (`member` mySet)
    where mySet = charClass s
{-# INLINE inClass #-}

-- | Match any character not in a set.
notInClass :: String -> Char -> Bool
notInClass s = not . inClass s
{-# INLINE notInClass #-}

-- | Match any character.
anyChar :: Parser Char
anyChar = satisfy $ const True
{-# INLINE anyChar #-}

-- | Match a specific character.
char :: Char -> Parser Char
char c = satisfy (== c) <?> show c
{-# INLINE char #-}

-- | Match any character except the given one.
notChar :: Char -> Parser Char
notChar c = satisfy (/= c) <?> "not " ++ show c
{-# INLINE notChar #-}

-- | Match only if all input has been consumed.
endOfInput :: Parser ()
endOfInput = Parser $ \st0@S{..} kf ks ->
             if T.null input
             then if more == Complete
                  then ks st0 ()
                  else let kf' st1 _ _ = ks (mappend st0 st1) ()
                           ks' st1 _   = kf (mappend st0 st1) [] "endOfInput"
                       in  runParser demandInput st0 kf' ks'
             else kf st0 [] "endOfInput"

-- | Match either a single newline character @\'\\n\'@, or a carriage
-- return followed by a newline character @\"\\r\\n\"@.
endOfLine :: Parser ()
endOfLine = (char '\n' >> return ()) <|> (string (T.pack "\r\n") >> return ())

--- | Name the parser, in case failure occurs.
(<?>) :: Parser a
      -> String                 -- ^ the name to use if parsing fails
      -> Parser a
p <?> msg = Parser $ \s kf ks -> runParser p s (\s' strs m -> kf s' (msg:strs) m) ks
{-# INLINE (<?>) #-}
infix 0 <?>

-- | Terminal failure continuation.
failK :: Failure a
failK st0 stack msg = Fail st0 stack msg

-- | Terminal success continuation.
successK :: Success a a
successK state a = Done state a

-- | Run a parser.
parse :: Parser a -> T.Text -> Result a
parse m s = runParser m (S s T.empty Incomplete) failK successK
{-# INLINE parse #-}