ref: dfda74cbaf3d2f129cc4d7da87435464f00a29fe
dir: /lib/Text/ParserCombinators/ReadP.hs/
{-# LANGUAGE Trustworthy #-}
{-# LANGUAGE NoImplicitPrelude #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE MagicHash #-}
{-# LANGUAGE DeriveFunctor #-}
-----------------------------------------------------------------------------
-- |
-- Module : GHC.Internal.Text.ParserCombinators.ReadP
-- Copyright : (c) The University of Glasgow 2002
-- License : BSD-style (see the file libraries/base/LICENSE)
--
-- Maintainer : libraries@haskell.org
-- Stability : provisional
-- Portability : non-portable (local universal quantification)
--
-- This is a library of parser combinators, originally written by Koen Claessen.
-- It parses all alternatives in parallel, so it never keeps hold of
-- the beginning of the input string, a common source of space leaks with
-- other parsers. The @('+++')@ choice combinator is genuinely commutative;
-- it makes no difference which branch is \"shorter\".
-----------------------------------------------------------------------------
module Text.ParserCombinators.ReadP
(
-- * The 'ReadP' type
ReadP,
-- * Primitive operations
get,
look,
(+++),
(<++),
gather,
-- * Other operations
pfail,
eof,
satisfy,
char,
string,
munch,
munch1,
skipSpaces,
choice,
count,
between,
option,
optional,
many,
many1,
skipMany,
skipMany1,
sepBy,
sepBy1,
endBy,
endBy1,
chainr,
chainl,
chainl1,
chainr1,
manyTill,
-- * Running a parser
ReadS,
readP_to_S,
readS_to_P,
-- * Properties
-- $properties
)
where
import Prelude()
import Primitives
import Control.Applicative hiding (optional, many)
import Control.Error
import Control.Monad
import Control.Monad.Fail
import Data.Bool
import Data.Char
import Data.Eq
import Data.Function
import Data.Functor
import Data.Int
import Data.Num
import Data.List
import Data.List.NonEmpty
import Data.Monoid.Internal
default (Int)
infixr 5 +++, <++
------------------------------------------------------------------------
-- ReadS
-- | A parser for a type @a@, represented as a function that takes a
-- 'String' and returns a list of possible parses as @(a,'String')@ pairs.
--
-- Note that this kind of backtracking parser is very inefficient;
-- reading a large structure may be quite slow (cf 'ReadP').
type ReadS a = String -> [(a,String)]
-- ---------------------------------------------------------------------------
-- The P type
-- is representation type -- should be kept abstract
data P a
= Get (Char -> P a)
| Look (String -> P a)
| Fail
| Result a (P a)
| Final (NonEmpty (a,String))
-- deriving Functor -- ^ @since base-4.8.0.0
instance Functor P where
fmap f (Get g) = Get (fmap f . g)
fmap f (Look g) = Look (fmap f . g)
fmap _ Fail = Fail
fmap f (Result a pa) = Result (f a) (fmap f pa)
fmap f (Final xs) = Final (fmap (\ (a, s) -> (f a, s)) xs)
-- Monad, MonadPlus
-- | @since base-4.5.0.0
instance Applicative P where
pure x = Result x Fail
(<*>) = ap
-- | @since base-2.01
instance MonadPlus P
-- | @since base-2.01
instance Monad P where
(Get f) >>= k = Get (\c -> f c >>= k)
(Look f) >>= k = Look (\s -> f s >>= k)
Fail >>= _ = Fail
(Result x p) >>= k = k x <|> (p >>= k)
(Final (r:|rs)) >>= k = final [ys' | (x,s) <- (r:rs), ys' <- run (k x) s]
-- | @since base-4.9.0.0
instance MonadFail P where
fail _ = Fail
-- | @since base-4.5.0.0
instance Alternative P where
empty = Fail
-- most common case: two gets are combined
Get f1 <|> Get f2 = Get (\c -> f1 c <|> f2 c)
-- results are delivered as soon as possible
Result x p <|> q = Result x (p <|> q)
p <|> Result x q = Result x (p <|> q)
-- fail disappears
Fail <|> p = p
p <|> Fail = p
-- two finals are combined
-- final + look becomes one look and one final (=optimization)
-- final + sthg else becomes one look and one final
Final r <|> Final t = Final (r <> t)
Final (r:|rs) <|> Look f = Look (\s -> Final (r:|(rs ++ run (f s) s)))
Final (r:|rs) <|> p = Look (\s -> Final (r:|(rs ++ run p s)))
Look f <|> Final r = Look (\s -> Final (case run (f s) s of
[] -> r
(x:xs) -> (x:|xs) <> r))
p <|> Final r = Look (\s -> Final (case run p s of
[] -> r
(x:xs) -> (x:|xs) <> r))
-- two looks are combined (=optimization)
-- look + sthg else floats upwards
Look f <|> Look g = Look (\s -> f s <|> g s)
Look f <|> p = Look (\s -> f s <|> p)
p <|> Look f = Look (\s -> p <|> f s)
-- ---------------------------------------------------------------------------
-- The ReadP type
newtype ReadP a = R (forall b . (a -> P b) -> P b)
-- | @since base-2.01
instance Functor ReadP where
fmap h (R f) = R (\k -> f (k . h))
-- | @since base-4.6.0.0
instance Applicative ReadP where
pure x = R (\k -> k x)
(<*>) = ap
-- liftA2 = liftM2
-- | @since base-2.01
instance Monad ReadP where
R m >>= f = R (\k -> m (\a -> let R m' = f a in m' k))
-- | @since base-4.9.0.0
instance MonadFail ReadP where
fail _ = R (\_ -> Fail)
-- | @since base-4.6.0.0
instance Alternative ReadP where
empty = pfail
(<|>) = (+++)
-- | @since base-2.01
instance MonadPlus ReadP
-- ---------------------------------------------------------------------------
-- Operations over P
final :: [(a,String)] -> P a
final [] = Fail
final (r:rs) = Final (r:|rs)
run :: P a -> ReadS a
run (Get f) (c:s) = run (f c) s
run (Look f) s = run (f s) s
run (Result x p) s = (x,s) : run p s
run (Final (r:|rs)) _ = (r:rs)
run _ _ = []
-- ---------------------------------------------------------------------------
-- Operations over ReadP
get :: ReadP Char
-- ^ Consumes and returns the next character.
-- Fails if there is no input left.
get = R Get
look :: ReadP String
-- ^ Look-ahead: returns the part of the input that is left, without
-- consuming it.
look = R Look
pfail :: ReadP a
-- ^ Always fails.
pfail = R (\_ -> Fail)
(+++) :: ReadP a -> ReadP a -> ReadP a
-- ^ Symmetric choice.
R f1 +++ R f2 = R (\k -> f1 k <|> f2 k)
(<++) :: forall a . ReadP a -> ReadP a -> ReadP a
-- ^ Local, exclusive, left-biased choice: If left parser
-- locally produces any result at all, then right parser is
-- not used.
(<++) (R f0) q =
do s <- look
probe (f0 return) s 0
where
probe :: P a -> [Char] -> Int -> ReadP a
probe (Get f) (c:s) n = probe (f c) s (n + 1)
probe (Look f) s n = probe (f s) s n
probe p@(Result _ _) _ n = discard n >> R (p >>=)
probe (Final r) _ _ = R (Final r >>=)
probe _ _ _ = q
discard 0 = return ()
discard n = get >> discard (n - 1)
gather :: ReadP a -> ReadP (String, a)
-- ^ Transforms a parser into one that does the same, but
-- in addition returns the exact characters read.
-- IMPORTANT NOTE: 'gather' gives a runtime error if its first argument
-- is built using any occurrences of readS_to_P.
gather (R m)
= R (\k -> gath id (m (\a -> return (\s -> k (s,a)))))
where
gath :: (String -> String) -> P (String -> P b) -> P b
gath l (Get f) = Get (\c -> gath (l.(c:)) (f c))
gath _ Fail = Fail
gath l (Look f) = Look (\s -> gath l (f s))
gath l (Result k p) = k (l []) <|> gath l p
gath _ (Final _) = errorWithoutStackTrace "do not use readS_to_P in gather!"
-- ---------------------------------------------------------------------------
-- Derived operations
satisfy :: (Char -> Bool) -> ReadP Char
-- ^ Consumes and returns the next character, if it satisfies the
-- specified predicate.
satisfy p = do c <- get; if p c then return c else pfail
char :: Char -> ReadP Char
-- ^ Parses and returns the specified character.
char c = satisfy (c ==)
eof :: ReadP ()
-- ^ Succeeds iff we are at the end of input
eof = do { s <- look
; if null s then return ()
else pfail }
string :: String -> ReadP String
-- ^ Parses and returns the specified string.
string this = do s <- look; scan this s
where
scan [] _ = return this
scan (x:xs) (y:ys) | x == y = do _ <- get; scan xs ys
scan _ _ = pfail
munch :: (Char -> Bool) -> ReadP String
-- ^ Parses the first zero or more characters satisfying the predicate.
-- Always succeeds, exactly once having consumed all the characters
-- Hence NOT the same as (many (satisfy p))
munch p =
do s <- look
scan s
where
scan (c:cs) | p c = do _ <- get; s <- scan cs; return (c:s)
scan _ = return ""
munch1 :: (Char -> Bool) -> ReadP String
-- ^ Parses the first one or more characters satisfying the predicate.
-- Fails if none, else succeeds exactly once having consumed all the characters
-- Hence NOT the same as (many1 (satisfy p))
munch1 p =
do c <- get
if p c then do s <- munch p; return (c:s)
else pfail
choice :: [ReadP a] -> ReadP a
-- ^ Combines all parsers in the specified list.
choice [] = pfail
choice [p] = p
choice (p:ps) = p +++ choice ps
skipSpaces :: ReadP ()
-- ^ Skips all whitespace.
skipSpaces =
do s <- look
skip s
where
skip (c:s) | isSpace c = do _ <- get; skip s
skip _ = return ()
count :: Int -> ReadP a -> ReadP [a]
-- ^ @count n p@ parses @n@ occurrences of @p@ in sequence. A list of
-- results is returned.
count n p = sequence (replicate n p)
between :: ReadP open -> ReadP close -> ReadP a -> ReadP a
-- ^ @between open close p@ parses @open@, followed by @p@ and finally
-- @close@. Only the value of @p@ is returned.
between open close p = do _ <- open
x <- p
_ <- close
return x
option :: a -> ReadP a -> ReadP a
-- ^ @option x p@ will either parse @p@ or return @x@ without consuming
-- any input.
option x p = p +++ return x
optional :: ReadP a -> ReadP ()
-- ^ @optional p@ optionally parses @p@ and always returns @()@.
optional p = (p >> return ()) +++ return ()
many :: ReadP a -> ReadP [a]
-- ^ Parses zero or more occurrences of the given parser.
many p = return [] +++ many1 p
many1 :: ReadP a -> ReadP [a]
-- ^ Parses one or more occurrences of the given parser.
many1 p = liftM2 (:) p (many p)
skipMany :: ReadP a -> ReadP ()
-- ^ Like 'many', but discards the result.
skipMany p = many p >> return ()
skipMany1 :: ReadP a -> ReadP ()
-- ^ Like 'many1', but discards the result.
skipMany1 p = p >> skipMany p
sepBy :: ReadP a -> ReadP sep -> ReadP [a]
-- ^ @sepBy p sep@ parses zero or more occurrences of @p@, separated by @sep@.
-- Returns a list of values returned by @p@.
sepBy p sep = sepBy1 p sep +++ return []
sepBy1 :: ReadP a -> ReadP sep -> ReadP [a]
-- ^ @sepBy1 p sep@ parses one or more occurrences of @p@, separated by @sep@.
-- Returns a list of values returned by @p@.
sepBy1 p sep = liftM2 (:) p (many (sep >> p))
endBy :: ReadP a -> ReadP sep -> ReadP [a]
-- ^ @endBy p sep@ parses zero or more occurrences of @p@, separated and ended
-- by @sep@.
endBy p sep = many (do x <- p ; _ <- sep ; return x)
endBy1 :: ReadP a -> ReadP sep -> ReadP [a]
-- ^ @endBy p sep@ parses one or more occurrences of @p@, separated and ended
-- by @sep@.
endBy1 p sep = many1 (do x <- p ; _ <- sep ; return x)
chainr :: ReadP a -> ReadP (a -> a -> a) -> a -> ReadP a
-- ^ @chainr p op x@ parses zero or more occurrences of @p@, separated by @op@.
-- Returns a value produced by a /right/ associative application of all
-- functions returned by @op@. If there are no occurrences of @p@, @x@ is
-- returned.
chainr p op x = chainr1 p op +++ return x
chainl :: ReadP a -> ReadP (a -> a -> a) -> a -> ReadP a
-- ^ @chainl p op x@ parses zero or more occurrences of @p@, separated by @op@.
-- Returns a value produced by a /left/ associative application of all
-- functions returned by @op@. If there are no occurrences of @p@, @x@ is
-- returned.
chainl p op x = chainl1 p op +++ return x
chainr1 :: ReadP a -> ReadP (a -> a -> a) -> ReadP a
-- ^ Like 'chainr', but parses one or more occurrences of @p@.
chainr1 p op = scan
where scan = p >>= rest
rest x = do f <- op
y <- scan
return (f x y)
+++ return x
chainl1 :: ReadP a -> ReadP (a -> a -> a) -> ReadP a
-- ^ Like 'chainl', but parses one or more occurrences of @p@.
chainl1 p op = p >>= rest
where rest x = do f <- op
y <- p
rest (f x y)
+++ return x
manyTill :: ReadP a -> ReadP end -> ReadP [a]
-- ^ @manyTill p end@ parses zero or more occurrences of @p@, until @end@
-- succeeds. Returns a list of values returned by @p@.
manyTill p end = scan
where scan = (end >> return []) <++ (liftM2 (:) p scan)
-- ---------------------------------------------------------------------------
-- Converting between ReadP and Read
readP_to_S :: ReadP a -> ReadS a
-- ^ Converts a parser into a Haskell ReadS-style function.
-- This is the main way in which you can \"run\" a 'ReadP' parser:
-- the expanded type is
-- @ readP_to_S :: ReadP a -> String -> [(a,String)] @
readP_to_S (R f) = run (f return)
readS_to_P :: ReadS a -> ReadP a
-- ^ Converts a Haskell ReadS-style function into a parser.
-- Warning: This introduces local backtracking in the resulting
-- parser, and therefore a possible inefficiency.
readS_to_P r =
R (\k -> Look (\s -> final [bs'' | (a,s') <- r s, bs'' <- run (k a) s']))