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GHC 9.14.1 · lts/ghc-9.14.x · 7a6c33e · 2026-10-12

Modulecabal-install-3.16.0.0Haskell2010

Distribution.Deprecated.ReadP

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".

See also Koen's paper Parallel Parsing Processes (http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.19.9217).

This version of ReadP has been locally hacked to make it H98, by Martin Sjögren mailto:msjogren@gmail.com

The unit tests have been moved to UnitTest.Distribution.Deprecated.ReadP, by Mark Lentczner mailto:mark@glyphic.com

Contents

The ReadP type
Primitive operations
Other operations
Running a parser
Internal

Synopsis

Packagecabal-install-3.16.0.0
Exports38
LanguageHaskell2010
LicenceBSD-3-Clause
SourceReadP.hs

The ReadP type

typetype ReadP r a = Parser r Char a

Primitive operations

valueget :: ReadP r Char

Consumes and returns the next character. Fails if there is no input left.

valuelook :: ReadP r String

Look-ahead: returns the part of the input that is left, without consuming it.

value(+++) :: ReadP r a -> ReadP r a -> ReadP r a

Symmetric choice.

value(<++) :: ReadP a a -> ReadP r a -> ReadP r a

Local, exclusive, left-biased choice: If left parser locally produces any result at all, then right parser is not used.

valuegather :: ReadP (String -> P Char r) a -> ReadP r (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.

Other operations

valuepfail :: ReadP r a

Always fails.

valueeof :: ReadP r ()

Succeeds iff we are at the end of input

valuesatisfy :: (Char -> Bool) -> ReadP r Char

Consumes and returns the next character, if it satisfies the specified predicate.

valuechar :: Char -> ReadP r Char

Parses and returns the specified character.

valuestring :: String -> ReadP r String

Parses and returns the specified string.

valuemunch :: (Char -> Bool) -> ReadP r String

Parses the first zero or more characters satisfying the predicate.

valuemunch1 :: (Char -> Bool) -> ReadP r String

Parses the first one or more characters satisfying the predicate.

valueskipSpaces :: ReadP r ()

Skips all whitespace.

valueskipSpaces1 :: ReadP r ()

Like skipSpaces but succeeds only if there is at least one whitespace character to skip.

valuechoice :: [ReadP r a] -> ReadP r a

Combines all parsers in the specified list.

valuecount :: Int -> ReadP r a -> ReadP r [a]

count n p parses n occurrences of p in sequence. A list of results is returned.

valuebetween :: ReadP r open -> ReadP r close -> ReadP r a -> ReadP r a

between open close p parses open, followed by p and finally close. Only the value of p is returned.

valueoption :: a -> ReadP r a -> ReadP r a

option x p will either parse p or return x without consuming any input.

valueoptional :: ReadP r a -> ReadP r ()

optional p optionally parses p and always returns ().

valuemany :: ReadP r a -> ReadP r [a]

Parses zero or more occurrences of the given parser.

valuemany1 :: ReadP r a -> ReadP r [a]

Parses one or more occurrences of the given parser.

valueskipMany :: ReadP r a -> ReadP r ()

Like many, but discards the result.

valueskipMany1 :: ReadP r a -> ReadP r ()

Like many1, but discards the result.

valuesepBy :: ReadP r a -> ReadP r sep -> ReadP r [a]

sepBy p sep parses zero or more occurrences of p, separated by sep. Returns a list of values returned by p.

valuesepBy1 :: ReadP r a -> ReadP r sep -> ReadP r [a]

sepBy1 p sep parses one or more occurrences of p, separated by sep. Returns a list of values returned by p.

valueendBy :: ReadP r a -> ReadP r sep -> ReadP r [a]

endBy p sep parses zero or more occurrences of p, separated and ended by sep.

valueendBy1 :: ReadP r a -> ReadP r sep -> ReadP r [a]

endBy p sep parses one or more occurrences of p, separated and ended by sep.

valuechainr :: ReadP r a -> ReadP r (a -> a -> a) -> a -> ReadP r 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.

valuechainl :: ReadP r a -> ReadP r (a -> a -> a) -> a -> ReadP r 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.

valuechainl1 :: ReadP r a -> ReadP r (a -> a -> a) -> ReadP r a

Like chainl, but parses one or more occurrences of p.

valuechainr1 :: ReadP r a -> ReadP r (a -> a -> a) -> ReadP r a

Like chainr, but parses one or more occurrences of p.

valuemanyTill :: ReadP r a -> ReadP [a] end -> ReadP r [a]

manyTill p end parses zero or more occurrences of p, until end succeeds. Returns a list of values returned by p.

Running a parser

typetype ReadS a = String -> [(a, String)]

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).

valuereadP_to_S :: ReadP a 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)]

valuereadS_to_P :: ReadS a -> ReadP r a

Converts a Haskell ReadS-style function into a parser. Warning: This introduces local backtracking in the resulting parser, and therefore a possible inefficiency.

valuereadP_to_E :: (String -> String) -> ReadP a a -> ReadE a

Internal

newtypenewtype Parser r s a

Instances6Monad, Functor, MonadFail, Applicative, Alternative, MonadPlus

Monad (Parser r s)Defined in cabal-install-3.16.0.0 · Distribution.Deprecated.ReadP
Functor (Parser r s)Defined in cabal-install-3.16.0.0 · Distribution.Deprecated.ReadP
MonadFail (Parser r s)Defined in cabal-install-3.16.0.0 · Distribution.Deprecated.ReadP
Applicative (Parser r s)Defined in cabal-install-3.16.0.0 · Distribution.Deprecated.ReadP
s ~ Char => Alternative (Parser r s)Defined in cabal-install-3.16.0.0 · Distribution.Deprecated.ReadP
s ~ Char => MonadPlus (Parser r s)Defined in cabal-install-3.16.0.0 · Distribution.Deprecated.ReadP