| Copyright | (c) Edward Kmett 2011-2012 | 
|---|---|
| License | BSD3 | 
| Maintainer | ekmett@gmail.com | 
| Stability | experimental | 
| Portability | non-portable | 
| Safe Haskell | Safe-Inferred | 
| 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 #
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 #
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.
It is useful for modelling any computation that is allowed to fail.
Examples
Using the Alternative instance of Except, the following functions:
>>>canFail = throwError "it failed" :: Except String Int>>>final = return 42 :: Except String Int
Can be combined by allowing the first function to fail:
>>>runExcept $ canFail *> finalLeft "it failed">>>runExcept $ optional canFail *> finalRight 42
skipOptional :: Alternative m => m a -> m () #
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 #
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] #
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) #
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) #
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] #
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) #
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] #
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] #
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 #
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 #
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 #
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 #
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] #
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 #
Additional functionality needed to describe parsers independent of input type.
Minimal complete definition
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 #
Give a parser a name
A version of many that discards its input. Specialized because it can often be implemented more cheaply.
skipSome p applies the parser p one or more times, skipping
 its result. (aka skipMany1 in parsec)
unexpected :: String -> m a #
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 () #
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