| Copyright | (c) Edward Kmett 2011-2012 |
|---|---|
| License | BSD3 |
| Maintainer | ekmett@gmail.com |
| Stability | experimental |
| Portability | non-portable |
| Safe Haskell | None |
| Language | Haskell2010 |
Distribution.Compat.Parsing
Contents
Description
Alternative parser combinators.
Originally in
parsers
package.
Synopsis
- choice :: Alternative m => [m a] -> m a
- option :: Alternative m => a -> m a -> m a
- optional :: Alternative f => f a -> f ( Maybe a)
- skipOptional :: Alternative m => m a -> m ()
- between :: Applicative m => m bra -> m ket -> m a -> m a
- some :: Alternative f => f a -> f [a]
- many :: Alternative f => f a -> f [a]
- sepBy :: Alternative m => m a -> m sep -> m [a]
- sepByNonEmpty :: Alternative m => m a -> m sep -> m ( NonEmpty a)
- sepEndByNonEmpty :: Alternative m => m a -> m sep -> m ( NonEmpty a)
- sepEndBy :: Alternative m => m a -> m sep -> m [a]
- endByNonEmpty :: Alternative m => m a -> m sep -> m ( NonEmpty a)
- endBy :: Alternative m => m a -> m sep -> m [a]
- count :: Applicative m => Int -> m a -> m [a]
- chainl :: Alternative m => m a -> m (a -> a -> a) -> a -> m a
- chainr :: Alternative m => m a -> m (a -> a -> a) -> a -> m a
- chainl1 :: Alternative m => m a -> m (a -> a -> a) -> m a
- chainr1 :: Alternative m => m a -> m (a -> a -> a) -> m a
- manyTill :: Alternative m => m a -> m end -> m [a]
-
class
Alternative
m =>
Parsing
m
where
- try :: m a -> m a
- (<?>) :: m a -> String -> m a
- skipMany :: m a -> m ()
- skipSome :: m a -> m ()
- unexpected :: String -> m a
- eof :: m ()
- notFollowedBy :: Show a => m a -> m ()
Parsing Combinators
choice :: Alternative m => [m a] -> 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.
option :: Alternative m => a -> m a -> 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 (digitToInt <$> digit)
optional :: Alternative f => f a -> f ( Maybe a) Source #
One or none.
skipOptional :: Alternative m => m a -> m () Source #
skipOptional 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
. (Plays the role of parsec's optional, which conflicts with Applicative's optional)
between :: Applicative m => m bra -> m ket -> m a -> m a Source #
between open close p
parses
open
, followed by
p
and
close
.
Returns the value returned by
p
.
braces = between (symbol "{") (symbol "}")
some :: Alternative f => f a -> f [a] Source #
One or more.
many :: Alternative f => f a -> f [a] Source #
Zero or more.
sepBy :: Alternative m => m a -> m sep -> 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 ",")
sepByNonEmpty :: Alternative m => m a -> m sep -> m ( NonEmpty a) Source #
sepByNonEmpty p sep
parses
one
or more occurrences of
p
, separated
by
sep
. Returns a non-empty list of values returned by
p
.
sepEndByNonEmpty :: Alternative m => m a -> m sep -> m ( NonEmpty a) Source #
sepEndByNonEmpty p sep
parses
one
or more occurrences of
p
,
separated and optionally ended by
sep
. Returns a non-empty list of values
returned by
p
.
sepEndBy :: Alternative m => m a -> m sep -> 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
endByNonEmpty :: Alternative m => m a -> m sep -> m ( NonEmpty a) Source #
endByNonEmpty p sep
parses
one
or more occurrences of
p
, separated
and ended by
sep
. Returns a non-empty list of values returned by
p
.
endBy :: Alternative m => m a -> m sep -> 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
count :: Applicative m => Int -> m a -> 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
.
chainl :: Alternative m => m a -> m (a -> a -> a) -> a -> 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.
chainr :: Alternative m => m a -> m (a -> a -> a) -> a -> 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.
chainl1 :: Alternative m => m a -> m (a -> a -> a) -> m a Source #
chainl1 p op x
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 = (*) <$ symbol "*"
<|> div <$ symbol "/"
addop = (+) <$ symbol "+"
<|> (-) <$ symbol "-"
chainr1 :: Alternative m => m a -> m (a -> a -> a) -> 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
.
manyTill :: Alternative m => m a -> m end -> 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.
Parsing Class
class Alternative m => Parsing m where Source #
Additional functionality needed to describe parsers independent of input type.
Minimal complete definition
try , (<?>) , unexpected , eof , notFollowedBy
Methods
Take a parser that may consume input, and on failure, go back to where we started and fail as if we didn't consume input.
(<?>) :: m a -> String -> m a infixr 0 Source #
Give a parser a name
skipMany :: m a -> m () Source #
A version of many that discards its input. Specialized because it can often be implemented more cheaply.
skipSome :: m a -> m () Source #
skipSome p
applies the parser
p
one
or more times, skipping
its result. (aka skipMany1 in parsec)
unexpected :: String -> m a Source #
Used to emit an error on an unexpected token
This parser only succeeds at the end of the input. This is not a
primitive parser but it is defined using
notFollowedBy
.
eof = notFollowedBy anyChar <?> "end of input"
notFollowedBy :: Show a => m a -> 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 $ string "let" <* notFollowedBy alphaNum