Copyright | (c) Daan Leijen 1999-2001 (c) Paolo Martini 2007 |
---|---|
License | BSD-style (see the LICENSE file) |
Maintainer | [email protected] |
Stability | provisional |
Portability | portable |
Safe Haskell | Trustworthy |
Language | Haskell2010 |
Commonly used generic combinators.
See also the parser-combinators package for additional (and generalised) combinators.
choice :: Stream s m t => [ParsecT s u m a] -> ParsecT s u m a Source
choice ps
tries to apply the parsers in the list ps
in order, until one of them succeeds. Returns the value of the succeeding parser.
count :: Stream s m t => Int -> ParsecT s u m a -> ParsecT s u m [a] Source
count n p
parses n
occurrences of p
. If n
is smaller or equal to zero, the parser equals to return []
. Returns a list of n
values returned by p
.
between :: Stream s m t => ParsecT s u m open -> ParsecT s u m close -> ParsecT s u m a -> ParsecT s u m a Source
between open close p
parses open
, followed by p
and close
. Returns the value returned by p
.
braces = between (symbol "{") (symbol "}")
option :: Stream s m t => a -> ParsecT s u m a -> ParsecT s u m a Source
option x p
tries to apply parser p
. If p
fails without consuming input, it returns the value x
, otherwise the value returned by p
.
priority = option 0 (do{ d <- digit ; return (digitToInt d) })
optionMaybe :: Stream s m t => ParsecT s u m a -> ParsecT s u m (Maybe a) Source
optionMaybe p
tries to apply parser p
. If p
fails without consuming input, it return Nothing
, otherwise it returns Just
the value returned by p
.
optional :: Stream s m t => ParsecT s u m a -> ParsecT s u m () Source
optional p
tries to apply parser p
. It will parse p
or nothing. It only fails if p
fails after consuming input. It discards the result of p
.
skipMany1 :: Stream s m t => ParsecT s u m a -> ParsecT s u m () Source
skipMany1 p
applies the parser p
one or more times, skipping its result.
many1 :: Stream s m t => ParsecT s u m a -> ParsecT s u m [a] Source
many1 p
applies the parser p
one or more times. Returns a list of the returned values of p
.
word = many1 letter
sepBy :: Stream s m t => ParsecT s u m a -> ParsecT s u m sep -> ParsecT s u m [a] Source
sepBy p sep
parses zero or more occurrences of p
, separated by sep
. Returns a list of values returned by p
.
commaSep p = p `sepBy` (symbol ",")
sepBy1 :: Stream s m t => ParsecT s u m a -> ParsecT s u m sep -> ParsecT s u m [a] Source
sepBy1 p sep
parses one or more occurrences of p
, separated by sep
. Returns a list of values returned by p
.
endBy :: Stream s m t => ParsecT s u m a -> ParsecT s u m sep -> ParsecT s u m [a] Source
endBy p sep
parses zero or more occurrences of p
, separated and ended by sep
. Returns a list of values returned by p
.
cStatements = cStatement `endBy` semi
endBy1 :: Stream s m t => ParsecT s u m a -> ParsecT s u m sep -> ParsecT s u m [a] Source
endBy1 p sep
parses one or more occurrences of p
, separated and ended by sep
. Returns a list of values returned by p
.
sepEndBy :: Stream s m t => ParsecT s u m a -> ParsecT s u m sep -> ParsecT s u m [a] Source
sepEndBy p sep
parses zero or more occurrences of p
, separated and optionally ended by sep
, ie. haskell style statements. Returns a list of values returned by p
.
haskellStatements = haskellStatement `sepEndBy` semi
sepEndBy1 :: Stream s m t => ParsecT s u m a -> ParsecT s u m sep -> ParsecT s u m [a] Source
sepEndBy1 p sep
parses one or more occurrences of p
, separated and optionally ended by sep
. Returns a list of values returned by p
.
chainl :: Stream s m t => ParsecT s u m a -> ParsecT s u m (a -> a -> a) -> a -> ParsecT s u m a Source
chainl p op x
parses zero or more occurrences of p
, separated by op
. Returns a value obtained by a left associative application of all functions returned by op
to the values returned by p
. If there are zero occurrences of p
, the value x
is returned.
chainl1 :: Stream s m t => ParsecT s u m a -> ParsecT s u m (a -> a -> a) -> ParsecT s u m a Source
chainl1 p op
parses one or more occurrences of p
, separated by op
Returns a value obtained by a left associative application of all functions returned by op
to the values returned by p
. This parser can for example be used to eliminate left recursion which typically occurs in expression grammars.
expr = term `chainl1` addop term = factor `chainl1` mulop factor = parens expr <|> integer mulop = do{ symbol "*"; return (*) } <|> do{ symbol "/"; return (div) } addop = do{ symbol "+"; return (+) } <|> do{ symbol "-"; return (-) }
chainr :: Stream s m t => ParsecT s u m a -> ParsecT s u m (a -> a -> a) -> a -> ParsecT s u m a Source
chainr p op x
parses zero or more occurrences of p
, separated by op
Returns a value obtained by a right associative application of all functions returned by op
to the values returned by p
. If there are no occurrences of p
, the value x
is returned.
chainr1 :: Stream s m t => ParsecT s u m a -> ParsecT s u m (a -> a -> a) -> ParsecT s u m a Source
chainr1 p op x
parses one or more occurrences of |p|, separated by op
Returns a value obtained by a right associative application of all functions returned by op
to the values returned by p
.
eof :: (Stream s m t, Show t) => ParsecT s u m () Source
This parser only succeeds at the end of the input. This is not a primitive parser but it is defined using notFollowedBy
.
eof = notFollowedBy anyToken <?> "end of input"
notFollowedBy :: (Stream s m t, Show a) => ParsecT s u m a -> ParsecT s u m () Source
notFollowedBy p
only succeeds when parser p
fails. This parser does not consume any input. This parser can be used to implement the 'longest match' rule. For example, when recognizing keywords (for example let
), we want to make sure that a keyword is not followed by a legal identifier character, in which case the keyword is actually an identifier (for example lets
). We can program this behaviour as follows:
keywordLet = try (do{ string "let" ; notFollowedBy alphaNum })
NOTE: Currently, notFollowedBy
exhibits surprising behaviour when applied to a parser p
that doesn't consume any input; specifically
notFollowedBy . notFollowedBy
is not equivalent to lookAhead
, andnotFollowedBy eof
never fails.See haskell/parsec#8 for more details.
manyTill :: Stream s m t => ParsecT s u m a -> ParsecT s u m end -> ParsecT s u m [a] Source
manyTill p end
applies parser p
zero or more times until parser end
succeeds. Returns the list of values returned by p
. This parser can be used to scan comments:
simpleComment = do{ string "<!--" ; manyTill anyChar (try (string "-->")) }
Note the overlapping parsers anyChar
and string "-->"
, and therefore the use of the try
combinator.
lookAhead :: Stream s m t => ParsecT s u m a -> ParsecT s u m a Source
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.
anyToken :: (Stream s m t, Show t) => ParsecT s u m t Source
The parser anyToken
accepts any kind of token. It is for example used to implement eof
. Returns the accepted token.
As a more comprehensive alternative for debugging Parsec parsers, there's also the parsec-free package.
parserTrace :: (Show t, Stream s m t) => String -> ParsecT s u m () Source
parserTrace label
is an impure function, implemented with Debug.Trace that prints to the console the remaining parser state at the time it is invoked. It is intended to be used for debugging parsers by inspecting their intermediate states.
*> parseTest (oneOf "aeiou" >> parserTrace "label") "atest" label: "test" ...
Since: parsec-3.1.12.0
parserTraced :: (Stream s m t, Show t) => String -> ParsecT s u m b -> ParsecT s u m b Source
parserTraced label p
is an impure function, implemented with Debug.Trace that prints to the console the remaining parser state at the time it is invoked. It then continues to apply parser p
, and if p
fails will indicate that the label has been backtracked. It is intended to be used for debugging parsers by inspecting their intermediate states.
*> parseTest (oneOf "aeiou" >> parserTraced "label" (oneOf "nope")) "atest" label: "test" label backtracked parse error at (line 1, column 2): ...
Since: parsec-3.1.12.0
© The University of Glasgow and others
Licensed under a BSD-style license (see top of the page).
https://downloads.haskell.org/~ghc/8.8.3/docs/html/libraries/parsec-3.1.14.0/Text-Parsec-Combinator.html