| 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) |
| Safe Haskell | Trustworthy |
| Language | Haskell2010 |
Text.ParserCombinators.ReadP
Description
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".
ReadP typeLook-ahead: returns the part of the input that is left, without consuming it.
(<++) ::ReadP a ->ReadP a ->ReadP ainfixr 5Source#
Local, exclusive, left-biased choice: If left parser locally produces any result at all, then right parser is not used.
gather ::ReadP a ->ReadP (String, a)Source#
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.
satisfy :: (Char ->Bool) ->ReadPCharSource#
Consumes and returns the next character, if it satisfies the specified predicate.
munch :: (Char ->Bool) ->ReadPStringSource#
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))
munch1 :: (Char ->Bool) ->ReadPStringSource#
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))
skipSpaces ::ReadP ()Source#
Skips all whitespace.
count ::Int ->ReadP a ->ReadP [a]Source#
count n p parsesn occurrences ofp in sequence. A list of results is returned.
between ::ReadP open ->ReadP close ->ReadP a ->ReadP aSource#
between open close p parsesopen, followed byp and finallyclose. Only the value ofp is returned.
option :: a ->ReadP a ->ReadP aSource#
option x p will either parsep or returnx without consuming any input.
sepBy ::ReadP a ->ReadP sep ->ReadP [a]Source#
sepBy p sep parses zero or more occurrences ofp, separated bysep. Returns a list of values returned byp.
sepBy1 ::ReadP a ->ReadP sep ->ReadP [a]Source#
sepBy1 p sep parses one or more occurrences ofp, separated bysep. Returns a list of values returned byp.
endBy ::ReadP a ->ReadP sep ->ReadP [a]Source#
endBy p sep parses zero or more occurrences ofp, separated and ended bysep.
endBy1 ::ReadP a ->ReadP sep ->ReadP [a]Source#
endBy p sep parses one or more occurrences ofp, separated and ended bysep.
chainr ::ReadP a ->ReadP (a -> a -> a) -> a ->ReadP aSource#
chainr p op x parses zero or more occurrences ofp, separated byop. Returns a value produced by aright associative application of all functions returned byop. If there are no occurrences ofp,x is returned.
chainl ::ReadP a ->ReadP (a -> a -> a) -> a ->ReadP aSource#
chainl p op x parses zero or more occurrences ofp, separated byop. Returns a value produced by aleft associative application of all functions returned byop. If there are no occurrences ofp,x is returned.
chainl1 ::ReadP a ->ReadP (a -> a -> a) ->ReadP aSource#
Likechainl, but parses one or more occurrences ofp.
chainr1 ::ReadP a ->ReadP (a -> a -> a) ->ReadP aSource#
Likechainr, but parses one or more occurrences ofp.
manyTill ::ReadP a ->ReadP end ->ReadP [a]Source#
manyTill p end parses zero or more occurrences ofp, untilend succeeds. Returns a list of values returned byp.
readP_to_S ::ReadP a ->ReadS aSource#
Converts a parser into a Haskell ReadS-style function. This is the main way in which you can "run" aReadP parser: the expanded type is readP_to_S :: ReadP a -> String -> [(a,String)]
readS_to_P ::ReadS a ->ReadP aSource#
Converts a Haskell ReadS-style function into a parser. Warning: This introduces local backtracking in the resulting parser, and therefore a possible inefficiency.
The following are QuickCheck specifications of what the combinators do.These can be seen as formal specifications of the behavior of thecombinators.
For some values, we only care about the lists contents, not their order,
(=~) :: Ord a => [a] -> [a] -> Boolxs =~ ys = sort xs == sort ys
Here follow the properties:
>>>readP_to_S get [][]
\c str -> readP_to_S get (c:str) == [(c, str)]
\str -> readP_to_S look str == [(str, str)]
\str -> readP_to_S pfail str == []
\x str -> 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 ]
\this str -> readP_to_S (string this) (this ++ str) == [(this,str)]
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
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