{-# LANGUAGE CPP #-}
{-# LANGUAGE DeriveDataTypeable #-}
{-# LANGUAGE ExistentialQuantification #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE FunctionalDependencies #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE PolymorphicComponents #-}
{-# LANGUAGE Safe #-}
{-# LANGUAGE StandaloneDeriving #-}
{-# LANGUAGE UndecidableInstances #-}

{-# OPTIONS_GHC -fno-warn-name-shadowing #-}

-----------------------------------------------------------------------------
-- |
-- Module      :  Text.Parsec.Prim
-- Copyright   :  (c) Daan Leijen 1999-2001, (c) Paolo Martini 2007
-- License     :  BSD-style (see the LICENSE file)
--
-- Maintainer  :  derek.a.elkins@gmail.com
-- Stability   :  provisional
-- Portability :  portable
--
-- The primitive parser combinators.
--
-----------------------------------------------------------------------------

{-# OPTIONS_HADDOCK not-home #-}

module Text.Parsec.Prim
    ( unknownError
    , sysUnExpectError
    , unexpected
    , ParsecT
    , runParsecT
    , mkPT
    , Parsec
    , Consumed(..)
    , Reply(..)
    , State(..)
    , parsecMap
    , parserReturn
    , parserBind
    , mergeErrorReply
    , parserFail
    , parserZero
    , parserPlus
    , (<?>)
    , (<|>)
    , label
    , labels
    , lookAhead
    , Stream(..)
    , tokens
    , try
    , token
    , tokenPrim
    , tokenPrimEx
    , many
    , skipMany
    , manyAccum
    , runPT
    , runP
    , runParserT
    , runParser
    , parse
    , parseTest
    , getPosition
    , getInput
    , setPosition
    , setInput
    , getParserState
    , setParserState
    , updateParserState
    , getState
    , putState
    , modifyState
    , setState
    , updateState
    ) where


import Prelude hiding (sequence)
import qualified Data.ByteString.Lazy.Char8 as CL
import qualified Data.ByteString.Char8 as C

import Data.Typeable ( Typeable )

import qualified Data.Text as Text
import qualified Data.Text.Lazy as TextL

-- To define Monoid instance
import qualified Data.List.NonEmpty as NE
import Data.List ( genericReplicate )
import Data.Traversable (sequence)
import qualified Data.Functor as Functor ( Functor(..) )
import qualified Data.Semigroup as Semigroup ( Semigroup(..) )
import qualified Data.Monoid as Monoid ( Monoid(..) )

import qualified Control.Applicative as Applicative ( Applicative(..), Alternative(..), liftA2 )
import Control.Monad (MonadPlus (..), ap, void, liftM)
import Control.Monad.Trans (MonadTrans (lift), MonadIO (liftIO))
import Control.Monad.Identity (Identity, runIdentity)
import qualified Control.Monad.Fail as Fail

import Control.Monad.Reader.Class (MonadReader (..))
import Control.Monad.State.Class (MonadState (..))
import Control.Monad.Cont.Class (MonadCont (..))
import Control.Monad.Error.Class (MonadError (..))

import Text.Parsec.Pos
import Text.Parsec.Error

unknownError :: State s u -> ParseError
unknownError state        = newErrorUnknown (statePos state)

sysUnExpectError :: String -> SourcePos -> Reply s u a
sysUnExpectError msg pos  = Error (newErrorMessage (SysUnExpect msg) pos)

-- | The parser @unexpected msg@ always fails with an unexpected error
-- message @msg@ without consuming any input.
--
-- The parsers 'fail', ('<?>') and @unexpected@ are the three parsers
-- used to generate error messages. Of these, only ('<?>') is commonly
-- used. For an example of the use of @unexpected@, see the definition
-- of 'Text.Parsec.Combinator.notFollowedBy'.

unexpected :: (Stream s m t) => String -> ParsecT s u m a
unexpected msg
    = ParsecT $ \s _ _ _ eerr ->
      eerr $ newErrorMessage (UnExpect msg) (statePos s)

-- | ParserT monad transformer and Parser type

-- | @ParsecT s u m a@ is a parser with stream type @s@, user state type @u@,
-- underlying monad @m@ and return type @a@.  Parsec is strict in the user state.
-- If this is undesirable, simply use a data type like @data Box a = Box a@ and
-- the state type @Box YourStateType@ to add a level of indirection.

newtype ParsecT s u m a
    = ParsecT {unParser :: forall b .
                 State s u
              -> (a -> State s u -> ParseError -> m b) -- consumed ok
              -> (ParseError -> m b)                   -- consumed err
              -> (a -> State s u -> ParseError -> m b) -- empty ok
              -> (ParseError -> m b)                   -- empty err
              -> m b
             }
#if MIN_VERSION_base(4,7,0)
     deriving ( Typeable )
     -- GHC 7.6 doesn't like deriving instances of Typeable for types with
     -- non-* type-arguments.
#endif

-- | Low-level unpacking of the ParsecT type. To run your parser, please look to
-- runPT, runP, runParserT, runParser and other such functions.
runParsecT :: Monad m => ParsecT s u m a -> State s u -> m (Consumed (m (Reply s u a)))
{-# INLINABLE runParsecT #-}
runParsecT p s = unParser p s cok cerr eok eerr
    where cok a s' err = return . Consumed . return $ Ok a s' err
          cerr err = return . Consumed . return $ Error err
          eok a s' err = return . Empty . return $ Ok a s' err
          eerr err = return . Empty . return $ Error err

-- | Low-level creation of the ParsecT type. You really shouldn't have to do this.
mkPT :: Monad m => (State s u -> m (Consumed (m (Reply s u a)))) -> ParsecT s u m a
{-# INLINABLE mkPT #-}
mkPT k = ParsecT $ \s cok cerr eok eerr -> do
           cons <- k s
           case cons of
             Consumed mrep -> do
                       rep <- mrep
                       case rep of
                         Ok x s' err -> cok x s' err
                         Error err -> cerr err
             Empty mrep -> do
                       rep <- mrep
                       case rep of
                         Ok x s' err -> eok x s' err
                         Error err -> eerr err

type Parsec s u = ParsecT s u Identity

data Consumed a  = Consumed a
                 | Empty !a
    deriving ( Typeable )

data Reply s u a = Ok a !(State s u) ParseError
                 | Error ParseError
    deriving ( Typeable )

data State s u = State {
      stateInput :: s,
      statePos   :: !SourcePos,
      stateUser  :: !u
    }
    deriving ( Typeable )

-- | The 'Semigroup' instance for 'ParsecT' is used to append the result
-- of several parsers, for example:
--
-- @
-- (many $ char 'a') <> (many $ char 'b')
-- @
--
-- The above will parse a string like @"aabbb"@ and return a successful
-- parse result @"aabbb"@. Compare against the below which will
-- produce a result of @"bbb"@ for the same input:
--
-- @
-- (many $ char 'a') >> (many $ char 'b')
-- (many $ char 'a') *> (many $ char 'b')
-- @
--
-- @since 3.1.12
instance Semigroup.Semigroup a => Semigroup.Semigroup (ParsecT s u m a) where
    -- | Combines two parsers like '*>', '>>' and @do {...;...}@
    --  /but/ also combines their results with (<>) instead of
    --  discarding the first.
    (<>)     = Applicative.liftA2 (Semigroup.<>)

#if MIN_VERSION_base(4,8,0)
    sconcat  = fmap Semigroup.sconcat . sequence
#else
    sconcat  = fmap (Semigroup.sconcat . NE.fromList) . sequence . NE.toList
#endif
    stimes b = Semigroup.sconcat . NE.fromList . genericReplicate b

-- | The 'Monoid' instance for 'ParsecT' is used for the same purposes as
-- the 'Semigroup' instance.
--
-- @since 3.1.12
instance ( Monoid.Monoid a
         , Semigroup.Semigroup (ParsecT s u m a)
         ) => Monoid.Monoid (ParsecT s u m a) where
    -- | A parser that always succeeds, consumes no input, and
    --  returns the underlying 'Monoid''s 'mempty' value
    mempty = Applicative.pure Monoid.mempty

    -- | See 'ParsecT''s 'Semigroup.<>' implementation
    mappend = (Semigroup.<>)

    mconcat = Functor.fmap Monoid.mconcat . sequence

instance Functor Consumed where
    fmap f (Consumed x) = Consumed (f x)
    fmap f (Empty x)    = Empty (f x)

instance Functor (Reply s u) where
    fmap f (Ok x s e) = Ok (f x) s e
    fmap _ (Error e) = Error e -- XXX

instance Functor (ParsecT s u m) where
    fmap f p = parsecMap f p

parsecMap :: (a -> b) -> ParsecT s u m a -> ParsecT s u m b
parsecMap f p
    = ParsecT $ \s cok cerr eok eerr ->
      unParser p s (cok . f) cerr (eok . f) eerr

instance Applicative.Applicative (ParsecT s u m) where
    pure = parserReturn
    (<*>) = ap -- TODO: Can this be optimized?
    p1 *> p2 = p1 `parserBind` const p2
    p1 <* p2 = do { x1 <- p1 ; void p2 ; return x1 }

instance Applicative.Alternative (ParsecT s u m) where
    empty = mzero
    (<|>) = mplus

instance Monad (ParsecT s u m) where
    return = Applicative.pure
    p >>= f = parserBind p f
    (>>) = (Applicative.*>)
#if !MIN_VERSION_base(4,13,0)
    fail = Fail.fail
#endif

-- | @since 3.1.12.0
instance Fail.MonadFail (ParsecT s u m) where
    fail = parserFail

instance (MonadIO m) => MonadIO (ParsecT s u m) where
    liftIO = lift . liftIO

instance (MonadReader r m) => MonadReader r (ParsecT s u m) where
    ask = lift ask
    local f p = mkPT $ \s -> local f (runParsecT p s)

-- I'm presuming the user might want a separate, non-backtracking
-- state aside from the Parsec user state.
instance (MonadState s m) => MonadState s (ParsecT s' u m) where
    get = lift get
    put = lift . put

instance (MonadCont m) => MonadCont (ParsecT s u m) where
    callCC f = mkPT $ \s ->
          callCC $ \c ->
          runParsecT (f (\a -> mkPT $ \s' -> c (pack s' a))) s

     where pack s a= Empty $ return (Ok a s (unknownError s))

instance (MonadError e m) => MonadError e (ParsecT s u m) where
    throwError = lift . throwError
    p `catchError` h = mkPT $ \s ->
        runParsecT p s `catchError` \e ->
            runParsecT (h e) s

parserReturn :: a -> ParsecT s u m a
parserReturn x
    = ParsecT $ \s _ _ eok _ ->
      eok x s (unknownError s)

parserBind :: ParsecT s u m a -> (a -> ParsecT s u m b) -> ParsecT s u m b
{-# INLINE parserBind #-}
parserBind m k
  = ParsecT $ \s cok cerr eok eerr ->
    let
        -- consumed-okay case for m
        mcok x s err
          | errorIsUnknown err = unParser (k x) s cok cerr cok cerr
          | otherwise =
            let
                 -- if (k x) consumes, those go straigt up
                 pcok = cok
                 pcerr = cerr

                 -- if (k x) doesn't consume input, but is okay,
                 -- we still return in the consumed continuation
                 peok x s err' = cok x s (mergeError err err')

                 -- if (k x) doesn't consume input, but errors,
                 -- we return the error in the 'consumed-error'
                 -- continuation
                 peerr err' = cerr (mergeError err err')
            in  unParser (k x) s pcok pcerr peok peerr

        -- empty-ok case for m
        meok x s err
          | errorIsUnknown err = unParser (k x) s cok cerr eok eerr
          | otherwise =
            let
                -- in these cases, (k x) can return as empty
                pcok = cok
                peok x s err' = eok x s (mergeError err err')
                pcerr = cerr
                peerr err' = eerr (mergeError err err')
            in  unParser (k x) s pcok pcerr peok peerr
        -- consumed-error case for m
        mcerr = cerr

        -- empty-error case for m
        meerr = eerr

    in unParser m s mcok mcerr meok meerr


mergeErrorReply :: ParseError -> Reply s u a -> Reply s u a
mergeErrorReply err1 reply -- XXX where to put it?
    = case reply of
        Ok x state err2 -> Ok x state (mergeError err1 err2)
        Error err2      -> Error (mergeError err1 err2)

parserFail :: String -> ParsecT s u m a
parserFail msg
    = ParsecT $ \s _ _ _ eerr ->
      eerr $ newErrorMessage (Message msg) (statePos s)

instance MonadPlus (ParsecT s u m) where
    mzero = parserZero
    mplus p1 p2 = parserPlus p1 p2

-- | @parserZero@ always fails without consuming any input. @parserZero@ is defined
-- equal to the 'mzero' member of the 'MonadPlus' class and to the 'Control.Applicative.empty' member
-- of the 'Control.Applicative.Alternative' class.

parserZero :: ParsecT s u m a
parserZero
    = ParsecT $ \s _ _ _ eerr ->
      eerr $ unknownError s

parserPlus :: ParsecT s u m a -> ParsecT s u m a -> ParsecT s u m a
{-# INLINE parserPlus #-}
parserPlus m n
    = ParsecT $ \s cok cerr eok eerr ->
      let
          meerr err =
              let
                  neok y s' err' = eok y s' (mergeError err err')
                  neerr err' = eerr $ mergeError err err'
              in unParser n s cok cerr neok neerr
      in unParser m s cok cerr eok meerr

instance MonadTrans (ParsecT s u) where
    lift amb = ParsecT $ \s _ _ eok _ -> do
               a <- amb
               eok a s $ unknownError s

infix  0 <?>
infixr 1 <|>

-- | The parser @p \<?> msg@ behaves as parser @p@, but whenever the
-- parser @p@ fails /without consuming any input/, it replaces expect
-- error messages with the expect error message @msg@.
--
-- This is normally used at the end of a set alternatives where we want
-- to return an error message in terms of a higher level construct
-- rather than returning all possible characters. For example, if the
-- @expr@ parser from the 'try' example would fail, the error
-- message is: '...: expecting expression'. Without the @(\<?>)@
-- combinator, the message would be like '...: expecting \"let\" or
-- letter', which is less friendly.

(<?>) :: (ParsecT s u m a) -> String -> (ParsecT s u m a)
p <?> msg = label p msg

-- | This combinator implements choice. The parser @p \<|> q@ first
-- applies @p@. If it succeeds, the value of @p@ is returned. If @p@
-- fails /without consuming any input/, parser @q@ is tried. This
-- combinator is defined equal to the 'mplus' member of the 'MonadPlus'
-- class and the ('Control.Applicative.<|>') member of 'Control.Applicative.Alternative'.
--
-- The parser is called /predictive/ since @q@ is only tried when
-- parser @p@ didn't consume any input (i.e.. the look ahead is 1).
-- This non-backtracking behaviour allows for both an efficient
-- implementation of the parser combinators and the generation of good
-- error messages.

(<|>) :: (ParsecT s u m a) -> (ParsecT s u m a) -> (ParsecT s u m a)
p1 <|> p2 = mplus p1 p2

-- | A synonym for @\<?>@, but as a function instead of an operator.
label :: ParsecT s u m a -> String -> ParsecT s u m a
label p msg
  = labels p [msg]

labels :: ParsecT s u m a -> [String] -> ParsecT s u m a
labels p msgs =
    ParsecT $ \s cok cerr eok eerr ->
    let eok' x s' error = eok x s' $ if errorIsUnknown error
                  then error
                  else setExpectErrors error msgs
        eerr' err = eerr $ setExpectErrors err msgs

    in unParser p s cok cerr eok' eerr'

 where
   setExpectErrors err []         = setErrorMessage (Expect "") err
   setExpectErrors err [msg]      = setErrorMessage (Expect msg) err
   setExpectErrors err (msg:msgs)
       = foldr (\msg' err' -> addErrorMessage (Expect msg') err')
         (setErrorMessage (Expect msg) err) msgs

-- TODO: There should be a stronger statement that can be made about this

-- | An instance of @Stream@ has stream type @s@, underlying monad @m@ and token type @t@ determined by the stream
--
-- Some rough guidelines for a \"correct\" instance of Stream:
--
--    * unfoldM uncons gives the [t] corresponding to the stream
--
--    * A @Stream@ instance is responsible for maintaining the \"position within the stream\" in the stream state @s@.  This is trivial unless you are using the monad in a non-trivial way.

class (Monad m) => Stream s m t | s -> t where
    uncons :: s -> m (Maybe (t,s))

instance (Monad m) => Stream [tok] m tok where
    uncons []     = return $ Nothing
    uncons (t:ts) = return $ Just (t,ts)
    {-# INLINE uncons #-}


instance (Monad m) => Stream CL.ByteString m Char where
    uncons = return . CL.uncons

instance (Monad m) => Stream C.ByteString m Char where
    uncons = return . C.uncons

instance (Monad m) => Stream Text.Text m Char where
    uncons = return . Text.uncons
    {-# INLINE uncons #-}

instance (Monad m) => Stream TextL.Text m Char where
    uncons = return . TextL.uncons
    {-# INLINE uncons #-}


tokens :: (Stream s m t, Eq t)
       => ([t] -> String)      -- Pretty print a list of tokens
       -> (SourcePos -> [t] -> SourcePos)
       -> [t]                  -- List of tokens to parse
       -> ParsecT s u m [t]
{-# INLINE tokens #-}
tokens _ _ []
    = ParsecT $ \s _ _ eok _ ->
      eok [] s $ unknownError s
tokens showTokens nextposs tts@(tok:toks)
    = ParsecT $ \(State input pos u) cok cerr _eok eerr ->
    let
        errEof = (setErrorMessage (Expect (showTokens tts))
                  (newErrorMessage (SysUnExpect "") pos))

        errExpect x = (setErrorMessage (Expect (showTokens tts))
                       (newErrorMessage (SysUnExpect (showTokens [x])) pos))

        walk []     rs = ok rs
        walk (t:ts) rs = do
          sr <- uncons rs
          case sr of
            Nothing                 -> cerr $ errEof
            Just (x,xs) | t == x    -> walk ts xs
                        | otherwise -> cerr $ errExpect x

        ok rs = let pos' = nextposs pos tts
                    s' = State rs pos' u
                in cok tts s' (newErrorUnknown pos')
    in do
        sr <- uncons input
        case sr of
            Nothing         -> eerr $ errEof
            Just (x,xs)
                | tok == x  -> walk toks xs
                | otherwise -> eerr $ errExpect x

-- | The parser @try p@ behaves like parser @p@, except that it
-- pretends that it hasn't consumed any input when an error occurs.
--
-- This combinator is used whenever arbitrary look ahead is needed.
-- Since it pretends that it hasn't consumed any input when @p@ fails,
-- the ('<|>') combinator will try its second alternative even when the
-- first parser failed while consuming input.
--
-- The @try@ combinator can for example be used to distinguish
-- identifiers and reserved words. Both reserved words and identifiers
-- are a sequence of letters. Whenever we expect a certain reserved
-- word where we can also expect an identifier we have to use the @try@
-- combinator. Suppose we write:
--
-- >  expr        = letExpr <|> identifier <?> "expression"
-- >
-- >  letExpr     = do{ string "let"; ... }
-- >  identifier  = many1 letter
--
-- If the user writes \"lexical\", the parser fails with: @unexpected
-- \'x\', expecting \'t\' in \"let\"@. Indeed, since the ('<|>') combinator
-- only tries alternatives when the first alternative hasn't consumed
-- input, the @identifier@ parser is never tried (because the prefix
-- \"le\" of the @string \"let\"@ parser is already consumed). The
-- right behaviour can be obtained by adding the @try@ combinator:
--
-- >  expr        = letExpr <|> identifier <?> "expression"
-- >
-- >  letExpr     = do{ try (string "let"); ... }
-- >  identifier  = many1 letter

try :: ParsecT s u m a -> ParsecT s u m a
try p =
    ParsecT $ \s cok _ eok eerr ->
    unParser p s cok eerr eok eerr

-- | @lookAhead p@ parses @p@ without consuming any input.
--
-- If @p@ fails and consumes some input, so does @lookAhead@. Combine with 'try'
-- if this is undesirable.

lookAhead :: (Stream s m t) => ParsecT s u m a -> ParsecT s u m a
lookAhead p =
    ParsecT $ \s _ cerr eok eerr -> do
        let eok' a _ _ = eok a s (newErrorUnknown (statePos s))
        unParser p s eok' cerr eok' eerr

-- | The parser @token showTok posFromTok testTok@ accepts a token @t@
-- with result @x@ when the function @testTok t@ returns @'Just' x@. The
-- source position of the @t@ should be returned by @posFromTok t@ and
-- the token can be shown using @showTok t@.
--
-- This combinator is expressed in terms of 'tokenPrim'.
-- It is used to accept user defined token streams. For example,
-- suppose that we have a stream of basic tokens tupled with source
-- positions. We can then define a parser that accepts single tokens as:
--
-- >  mytoken x
-- >    = token showTok posFromTok testTok
-- >    where
-- >      showTok (pos,t)     = show t
-- >      posFromTok (pos,t)  = pos
-- >      testTok (pos,t)     = if x == t then Just t else Nothing

token :: (Stream s Identity t)
      => (t -> String)            -- ^ Token pretty-printing function.
      -> (t -> SourcePos)         -- ^ Computes the position of a token.
      -> (t -> Maybe a)           -- ^ Matching function for the token to parse.
      -> Parsec s u a
{-# INLINABLE token #-}
token showToken tokpos test = tokenPrim showToken nextpos test
    where
        nextpos _ tok ts = case runIdentity (uncons ts) of
                             Nothing -> tokpos tok
                             Just (tok',_) -> tokpos tok'

-- | The parser @tokenPrim showTok nextPos testTok@ accepts a token @t@
-- with result @x@ when the function @testTok t@ returns @'Just' x@. The
-- token can be shown using @showTok t@. The position of the /next/
-- token should be returned when @nextPos@ is called with the current
-- source position @pos@, the current token @t@ and the rest of the
-- tokens @toks@, @nextPos pos t toks@.
--
-- This is the most primitive combinator for accepting tokens. For
-- example, the 'Text.Parsec.Char.char' parser could be implemented as:
--
-- >  char c
-- >    = tokenPrim showChar nextPos testChar
-- >    where
-- >      showChar x        = "'" ++ x ++ "'"
-- >      testChar x        = if x == c then Just x else Nothing
-- >      nextPos pos x xs  = updatePosChar pos x

tokenPrim :: (Stream s m t)
          => (t -> String)                      -- ^ Token pretty-printing function.
          -> (SourcePos -> t -> s -> SourcePos) -- ^ Next position calculating function.
          -> (t -> Maybe a)                     -- ^ Matching function for the token to parse.
          -> ParsecT s u m a
{-# INLINE tokenPrim #-}
tokenPrim showToken nextpos test = tokenPrimEx showToken nextpos Nothing test

tokenPrimEx :: (Stream s m t)
            => (t -> String)
            -> (SourcePos -> t -> s -> SourcePos)
            -> Maybe (SourcePos -> t -> s -> u -> u)
            -> (t -> Maybe a)
            -> ParsecT s u m a
{-# INLINE tokenPrimEx #-}
tokenPrimEx showToken nextpos Nothing test
  = ParsecT $ \(State input pos user) cok _cerr _eok eerr -> do
      r <- uncons input
      case r of
        Nothing -> eerr $ unexpectError "" pos
        Just (c,cs)
         -> case test c of
              Just x -> let newpos = nextpos pos c cs
                            newstate = State cs newpos user
                        in seq newpos $ seq newstate $
                           cok x newstate (newErrorUnknown newpos)
              Nothing -> eerr $ unexpectError (showToken c) pos
tokenPrimEx showToken nextpos (Just nextState) test
  = ParsecT $ \(State input pos user) cok _cerr _eok eerr -> do
      r <- uncons input
      case r of
        Nothing -> eerr $ unexpectError "" pos
        Just (c,cs)
         -> case test c of
              Just x -> let newpos = nextpos pos c cs
                            newUser = nextState pos c cs user
                            newstate = State cs newpos newUser
                        in seq newpos $ seq newstate $
                           cok x newstate $ newErrorUnknown newpos
              Nothing -> eerr $ unexpectError (showToken c) pos

unexpectError :: String -> SourcePos -> ParseError
unexpectError msg pos = newErrorMessage (SysUnExpect msg) pos


-- | @many p@ applies the parser @p@ /zero/ or more times. Returns a
--    list of the returned values of @p@.
--
-- >  identifier  = do{ c  <- letter
-- >                  ; cs <- many (alphaNum <|> char '_')
-- >                  ; return (c:cs)
-- >                  }

many :: ParsecT s u m a -> ParsecT s u m [a]
many p
  = do xs <- manyAccum (:) p
       return (reverse xs)

-- | @skipMany p@ applies the parser @p@ /zero/ or more times, skipping
-- its result.
--
-- >  spaces  = skipMany space

skipMany :: ParsecT s u m a -> ParsecT s u m ()
skipMany p
  = do _ <- manyAccum (\_ _ -> []) p
       return ()

manyAccum :: (a -> [a] -> [a])
          -> ParsecT s u m a
          -> ParsecT s u m [a]
manyAccum acc p =
    ParsecT $ \s cok cerr eok _eerr ->
    let walk xs x s' _err =
            unParser p s'
              (seq xs $ walk $ acc x xs)  -- consumed-ok
              cerr                        -- consumed-err
              manyErr                     -- empty-ok
              (\e -> cok (acc x xs) s' e) -- empty-err
    in unParser p s (walk []) cerr manyErr (\e -> eok [] s e)

manyErr :: a
manyErr = error "Text.ParserCombinators.Parsec.Prim.many: combinator 'many' is applied to a parser that accepts an empty string."


-- < Running a parser: monadic (runPT) and pure (runP)

runPT :: (Stream s m t)
      => ParsecT s u m a -> u -> SourceName -> s -> m (Either ParseError a)
{-# INLINABLE runPT #-}
runPT p u name s
    = do res <- runParsecT p (State s (initialPos name) u)
         r <- parserReply res
         case r of
           Ok x _ _  -> return (Right x)
           Error err -> return (Left err)
    where
        parserReply res
            = case res of
                Consumed r -> r
                Empty    r -> r

runP :: (Stream s Identity t)
     => Parsec s u a -> u -> SourceName -> s -> Either ParseError a
runP p u name s = runIdentity $ runPT p u name s

-- | The most general way to run a parser. @runParserT p state filePath
-- input@ runs parser @p@ on the input list of tokens @input@,
-- obtained from source @filePath@ with the initial user state @st@.
-- The @filePath@ is only used in error messages and may be the empty
-- string. Returns a computation in the underlying monad @m@ that return either a 'ParseError' ('Left') or a
-- value of type @a@ ('Right').

runParserT :: (Stream s m t)
           => ParsecT s u m a -> u -> SourceName -> s -> m (Either ParseError a)
runParserT = runPT

-- | The most general way to run a parser over the Identity monad. @runParser p state filePath
-- input@ runs parser @p@ on the input list of tokens @input@,
-- obtained from source @filePath@ with the initial user state @st@.
-- The @filePath@ is only used in error messages and may be the empty
-- string. Returns either a 'ParseError' ('Left') or a
-- value of type @a@ ('Right').
--
-- >  parseFromFile p fname
-- >    = do{ input <- readFile fname
-- >        ; return (runParser p () fname input)
-- >        }

runParser :: (Stream s Identity t)
          => Parsec s u a -> u -> SourceName -> s -> Either ParseError a
runParser = runP

-- | @parse p filePath input@ runs a parser @p@ over Identity without user
-- state. The @filePath@ is only used in error messages and may be the
-- empty string. Returns either a 'ParseError' ('Left')
-- or a value of type @a@ ('Right').
--
-- >  main    = case (parse numbers "" "11, 2, 43") of
-- >             Left err  -> print err
-- >             Right xs  -> print (sum xs)
-- >
-- >  numbers = commaSep integer

parse :: (Stream s Identity t)
      => Parsec s () a -> SourceName -> s -> Either ParseError a
parse p = runP p ()

-- | The expression @parseTest p input@ applies a parser @p@ against
-- input @input@ and prints the result to stdout. Used for testing
-- parsers.

parseTest :: (Stream s Identity t, Show a)
          => Parsec s () a -> s -> IO ()
parseTest p input
    = case parse p "" input of
        Left err -> do putStr "parse error at "
                       print err
        Right x  -> print x

-- < Parser state combinators

-- | Returns the current source position. See also 'SourcePos'.

getPosition :: (Monad m) => ParsecT s u m SourcePos
getPosition = do state <- getParserState
                 return (statePos state)

-- | Returns the current input

getInput :: (Monad m) => ParsecT s u m s
getInput = do state <- getParserState
              return (stateInput state)

-- | @setPosition pos@ sets the current source position to @pos@.

setPosition :: (Monad m) => SourcePos -> ParsecT s u m ()
setPosition pos
    = do _ <- updateParserState (\(State input _ user) -> State input pos user)
         return ()

-- | @setInput input@ continues parsing with @input@. The 'getInput' and
-- @setInput@ functions can for example be used to deal with #include
-- files.

setInput :: (Monad m) => s -> ParsecT s u m ()
setInput input
    = do _ <- updateParserState (\(State _ pos user) -> State input pos user)
         return ()

-- | Returns the full parser state as a 'State' record.

getParserState :: (Monad m) => ParsecT s u m (State s u)
getParserState = updateParserState id

-- | @setParserState st@ set the full parser state to @st@.

setParserState :: (Monad m) => State s u -> ParsecT s u m (State s u)
setParserState st = updateParserState (const st)

-- | @updateParserState f@ applies function @f@ to the parser state.

updateParserState :: (State s u -> State s u) -> ParsecT s u m (State s u)
updateParserState f =
    ParsecT $ \s _ _ eok _ ->
    let s' = f s
    in eok s' s' $ unknownError s'

-- < User state combinators

-- | Returns the current user state.

getState :: (Monad m) => ParsecT s u m u
getState = stateUser `liftM` getParserState

-- | @putState st@ set the user state to @st@.

putState :: (Monad m) => u -> ParsecT s u m ()
putState u = do _ <- updateParserState $ \s -> s { stateUser = u }
                return ()

-- | @modifyState f@ applies function @f@ to the user state. Suppose
-- that we want to count identifiers in a source, we could use the user
-- state as:
--
-- >  expr  = do{ x <- identifier
-- >            ; modifyState (+1)
-- >            ; return (Id x)
-- >            }

modifyState :: (Monad m) => (u -> u) -> ParsecT s u m ()
modifyState f = do _ <- updateParserState $ \s -> s { stateUser = f (stateUser s) }
                   return ()

-- XXX Compat

-- | An alias for putState for backwards compatibility.

setState :: (Monad m) => u -> ParsecT s u m ()
setState = putState

-- | An alias for modifyState for backwards compatibility.

updateState :: (Monad m) => (u -> u) -> ParsecT s u m ()
updateState = modifyState
