{-# OPTIONS_GHC -fglasgow-exts -fno-implicit-prelude #-}
-----------------------------------------------------------------------------
-- |
-- Module : Text.ParserCombinators.ReadP
-- Copyright : (c) The University of Glasgow 2002
-- License : BSD-style (see the file libraries/base/LICENSE)
--
-- Maintainer : [email protected]
-- 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
#ifndef __NHC__
ReadP, -- :: * -> *; instance Functor, Monad, MonadPlus
#else
ReadPN, -- :: * -> * -> *; instance Functor, Monad, MonadPlus
#endif
-- * Primitive operations
get, -- :: ReadP Char
look, -- :: ReadP String
(+++), -- :: ReadP a -> ReadP a -> ReadP a
(<++), -- :: ReadP a -> ReadP a -> ReadP a
gather, -- :: ReadP a -> ReadP (String, a)
-- * Other operations
pfail, -- :: ReadP a
satisfy, -- :: (Char -> Bool) -> ReadP Char
char, -- :: Char -> ReadP Char
string, -- :: String -> ReadP String
munch, -- :: (Char -> Bool) -> ReadP String
munch1, -- :: (Char -> Bool) -> ReadP String
skipSpaces, -- :: ReadP ()
choice, -- :: [ReadP a] -> ReadP a
count, -- :: Int -> ReadP a -> ReadP [a]
between, -- :: ReadP open -> ReadP close -> ReadP a -> ReadP a
option, -- :: a -> ReadP a -> ReadP a
optional, -- :: ReadP a -> ReadP ()
many, -- :: ReadP a -> ReadP [a]
many1, -- :: ReadP a -> ReadP [a]
skipMany, -- :: ReadP a -> ReadP ()
skipMany1, -- :: ReadP a -> ReadP ()
sepBy, -- :: ReadP a -> ReadP sep -> ReadP [a]
sepBy1, -- :: ReadP a -> ReadP sep -> ReadP [a]
endBy, -- :: ReadP a -> ReadP sep -> ReadP [a]
endBy1, -- :: ReadP a -> ReadP sep -> ReadP [a]
chainr, -- :: ReadP a -> ReadP (a -> a -> a) -> a -> ReadP a
chainl, -- :: ReadP a -> ReadP (a -> a -> a) -> a -> ReadP a
chainl1, -- :: ReadP a -> ReadP (a -> a -> a) -> ReadP a
chainr1, -- :: ReadP a -> ReadP (a -> a -> a) -> ReadP a
manyTill, -- :: ReadP a -> ReadP end -> ReadP [a]
-- * Running a parser
ReadS, -- :: *; = String -> [(a,String)]
readP_to_S, -- :: ReadP a -> ReadS a
readS_to_P, -- :: ReadS a -> ReadP a
-- * Properties
-- $properties
)
where
import Control.Monad( MonadPlus(..), sequence, liftM2 )
#ifdef __GLASGOW_HASKELL__
#ifndef __HADDOCK__
import {-# SOURCE #-} GHC.Unicode ( isSpace )
#endif
import GHC.List ( replicate )
import GHC.Base
#else
import Data.Char( isSpace )
#endif
infixr 5 +++, <++
#ifdef __GLASGOW_HASKELL__
------------------------------------------------------------------------
-- 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)]
#endif
-- ---------------------------------------------------------------------------
-- 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 [(a,String)] -- invariant: list is non-empty!
-- Monad, MonadPlus
instance Monad P where
return x = Result x Fail
(Get f) >>= k = Get (\c -> f c >>= k)
(Look f) >>= k = Look (\s -> f s >>= k)
Fail >>= k = Fail
(Result x p) >>= k = k x `mplus` (p >>= k)
(Final r) >>= k = final [ys' | (x,s) <- r, ys' <- run (k x) s]
fail _ = Fail
instance MonadPlus P where
mzero = Fail
-- most common case: two gets are combined
Get f1 `mplus` Get f2 = Get (\c -> f1 c `mplus` f2 c)
-- results are delivered as soon as possible
Result x p `mplus` q = Result x (p `mplus` q)
p `mplus` Result x q = Result x (p `mplus` q)
-- fail disappears
Fail `mplus` p = p
p `mplus` 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 `mplus` Final t = Final (r ++ t)
Final r `mplus` Look f = Look (\s -> Final (r ++ run (f s) s))
Final r `mplus` p = Look (\s -> Final (r ++ run p s))
Look f `mplus` Final r = Look (\s -> Final (run (f s) s ++ r))
p `mplus` Final r = Look (\s -> Final (run p s ++ r))
-- two looks are combined (=optimization)
-- look + sthg else floats upwards
Look f `mplus` Look g = Look (\s -> f s `mplus` g s)
Look f `mplus` p = Look (\s -> f s `mplus` p)
p `mplus` Look f = Look (\s -> p `mplus` f s)
-- ---------------------------------------------------------------------------
-- The ReadP type
#ifndef __NHC__
newtype ReadP a = R (forall b . (a -> P b) -> P b)
#else
#define ReadP (ReadPN b)
newtype ReadPN b a = R ((a -> P b) -> P b)
#endif
-- Functor, Monad, MonadPlus
instance Functor ReadP where
fmap h (R f) = R (\k -> f (k . h))
instance Monad ReadP where
return x = R (\k -> k x)
fail _ = R (\_ -> Fail)
R m >>= f = R (\k -> m (\a -> let R m' = f a in m' k))
instance MonadPlus ReadP where
mzero = pfail
mplus = (+++)
-- ---------------------------------------------------------------------------
-- Operations over P
final :: [(a,String)] -> P a
-- Maintains invariant for Final constructor
final [] = Fail
final r = Final r
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) _ = r
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 `mplus` f2 k)
#ifndef __NHC__
(<++) :: ReadP a -> ReadP a -> ReadP a
#else
(<++) :: ReadPN a a -> ReadPN a a -> ReadPN a a
#endif
-- ^ Local, exclusive, left-biased choice: If left parser
-- locally produces any result at all, then right parser is
-- not used.
#ifdef __GLASGOW_HASKELL__
R f <++ q =
do s <- look
probe (f return) s 0#
where
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#)
#else
R f <++ q =
do s <- look
probe (f return) s 0
where
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)
#endif
#ifndef __NHC__
gather :: ReadP a -> ReadP (String, a)
#else
-- gather :: ReadPN (String->P b) a -> ReadPN (String->P b) (String, a)
#endif
-- ^ 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 l (Get f) = Get (\c -> gath (l.(c:)) (f c))
gath l Fail = Fail
gath l (Look f) = Look (\s -> gath l (f s))
gath l (Result k p) = k (l []) `mplus` gath l p
gath l (Final r) = error "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 ==)
string :: String -> ReadP String
-- ^ Parses and returns the specified string.
string this = do s <- look; scan this s
where
scan [] _ = do return this
scan (x:xs) (y:ys) | x == y = do get; scan xs ys
scan _ _ = do pfail
munch :: (Char -> Bool) -> ReadP String
-- ^ Parses the first zero or more characters satisfying the predicate.
munch p =
do s <- look
scan s
where
scan (c:cs) | p c = do get; s <- scan cs; return (c:s)
scan _ = do return ""
munch1 :: (Char -> Bool) -> ReadP String
-- ^ Parses the first one or more characters satisfying the predicate.
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 _ = do 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
#ifndef __NHC__
manyTill :: ReadP a -> ReadP end -> ReadP [a]
#else
manyTill :: ReadPN [a] a -> ReadPN [a] end -> ReadPN [a] [a]
#endif
-- ^ @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
#ifndef __NHC__
readP_to_S :: ReadP a -> ReadS a
#else
readP_to_S :: ReadPN a a -> ReadS a
#endif
-- ^ 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']))
-- ---------------------------------------------------------------------------
-- QuickCheck properties that hold for the combinators
{- $properties
The following are QuickCheck specifications of what the combinators do.
These can be seen as formal specifications of the behavior of the
combinators.
We use bags to give semantics to the combinators.
> type Bag a = [a]
Equality on bags does not care about the order of elements.
> (=~) :: Ord a => Bag a -> Bag a -> Bool
> xs =~ ys = sort xs == sort ys
A special equality operator to avoid unresolved overloading
when testing the properties.
> (=~.) :: Bag (Int,String) -> Bag (Int,String) -> Bool
> (=~.) = (=~)
Here follow the properties:
> prop_Get_Nil =
> readP_to_S get [] =~ []
>
> prop_Get_Cons c s =
> readP_to_S get (c:s) =~ [(c,s)]
>
> prop_Look s =
> readP_to_S look s =~ [(s,s)]
>
> prop_Fail s =
> readP_to_S pfail s =~. []
>
> prop_Return x s =
> readP_to_S (return x) s =~. [(x,s)]
>
> prop_Bind p k s =
> readP_to_S (p >>= k) s =~.
> [ ys''
> | (x,s') <- readP_to_S p s
> , ys'' <- readP_to_S (k (x::Int)) s'
> ]
>
> prop_Plus p q s =
> readP_to_S (p +++ q) s =~.
> (readP_to_S p s ++ readP_to_S q s)
>
> prop_LeftPlus p q s =
> readP_to_S (p <++ q) s =~.
> (readP_to_S p s +<+ readP_to_S q s)
> where
> [] +<+ ys = ys
> xs +<+ _ = xs
>
> prop_Gather s =
> forAll readPWithoutReadS $ \p ->
> readP_to_S (gather p) s =~
> [ ((pre,x::Int),s')
> | (x,s') <- readP_to_S p s
> , let pre = take (length s - length s') s
> ]
>
> prop_String_Yes this s =
> readP_to_S (string this) (this ++ s) =~
> [(this,s)]
>
> prop_String_Maybe this s =
> readP_to_S (string this) s =~
> [(this, drop (length this) s) | this `isPrefixOf` s]
>
> prop_Munch p s =
> readP_to_S (munch p) s =~
> [(takeWhile p s, dropWhile p s)]
>
> prop_Munch1 p s =
> readP_to_S (munch1 p) s =~
> [(res,s') | let (res,s') = (takeWhile p s, dropWhile p s), not (null res)]
>
> prop_Choice ps s =
> readP_to_S (choice ps) s =~.
> readP_to_S (foldr (+++) pfail ps) s
>
> prop_ReadS r s =
> readP_to_S (readS_to_P r) s =~. r s
-}
|
