Copyright | (c) Daan Leijen 1999-2001 (c) Paolo Martini 2007 |
---|---|
License | BSD-style (see the LICENSE file) |
Maintainer | derek.a.elkins@gmail.com |
Stability | provisional |
Portability | portable |
Safe Haskell | Trustworthy |
Language | Haskell2010 |
Text.Parsec.Combinator
Contents
Description
Commonly used generic combinators.
See also the parser-combinators package for additional (and generalised) combinators.
Synopsis
- choice :: Stream s m t => [ ParsecT s u m a] -> ParsecT s u m a
- count :: Stream s m t => Int -> ParsecT s u m a -> ParsecT s u m [a]
- 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
- option :: Stream s m t => a -> ParsecT s u m a -> ParsecT s u m a
- optionMaybe :: Stream s m t => ParsecT s u m a -> ParsecT s u m ( Maybe a)
- optional :: Stream s m t => ParsecT s u m a -> ParsecT s u m ()
- skipMany1 :: Stream s m t => ParsecT s u m a -> ParsecT s u m ()
- many1 :: Stream s m t => ParsecT s u m a -> ParsecT s u m [a]
- sepBy :: Stream s m t => ParsecT s u m a -> ParsecT s u m sep -> ParsecT s u m [a]
- sepBy1 :: Stream s m t => ParsecT s u m a -> ParsecT s u m sep -> ParsecT s u m [a]
- endBy :: Stream s m t => ParsecT s u m a -> ParsecT s u m sep -> ParsecT s u m [a]
- endBy1 :: Stream s m t => ParsecT s u m a -> ParsecT s u m sep -> ParsecT s u m [a]
- sepEndBy :: Stream s m t => ParsecT s u m a -> ParsecT s u m sep -> ParsecT s u m [a]
- sepEndBy1 :: Stream s m t => ParsecT s u m a -> ParsecT s u m sep -> ParsecT s u m [a]
- chainl :: Stream s m t => ParsecT s u m a -> ParsecT s u m (a -> a -> a) -> a -> ParsecT s u m a
- chainl1 :: Stream s m t => ParsecT s u m a -> ParsecT s u m (a -> a -> a) -> ParsecT s u m a
- chainr :: Stream s m t => ParsecT s u m a -> ParsecT s u m (a -> a -> a) -> a -> ParsecT s u m a
- chainr1 :: Stream s m t => ParsecT s u m a -> ParsecT s u m (a -> a -> a) -> ParsecT s u m a
- eof :: ( Stream s m t, Show t) => ParsecT s u m ()
- notFollowedBy :: ( Stream s m t, Show a) => ParsecT s u m a -> ParsecT s u m ()
- manyTill :: Stream s m t => ParsecT s u m a -> ParsecT s u m end -> ParsecT s u m [a]
- lookAhead :: Stream s m t => ParsecT s u m a -> ParsecT s u m a
- anyToken :: ( Stream s m t, Show t) => ParsecT s u m t
- parserTrace :: ( Show t, Stream s m t) => String -> ParsecT s u m ()
- parserTraced :: ( Stream s m t, Show t) => String -> ParsecT s u m b -> ParsecT s u m b
Documentation
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) })
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
lookAhead
, and -
notFollowedBy
eof
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.
Debugging
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: 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: 3.1.12.0