Copyright	(c) Edward Kmett 2011-2012
License	BSD3
Maintainer	ekmett@gmail.com
Stability	experimental
Portability	non-portable
Safe Haskell	None
Language	Haskell2010

Text.Parser.Combinators

Contents

Parsing Combinators
Parsing Class

Description

Alternative parser combinators

Synopsis

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)

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 => forall a. f a -> f [a]

One or more.

many :: Alternative f => forall a. f a -> f [a]

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 ",")

sepBy1 :: Alternative m => m a -> m sep -> m [a] Source

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

sepEndBy1 :: Alternative m => m a -> m sep -> 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.

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

endBy1 :: Alternative m => m a -> m sep -> m [a] Source

endBy1 p sep parses one or more occurrences of p, seperated and ended by sep. Returns a 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, seperated 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 parser 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 parser 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 parser 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 parser 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, (<?>), notFollowedBy

Methods

try :: m a -> m a Source

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

eof :: 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 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

Instances

Parsing ReadP
Chunk t => Parsing (Parser t)
(Parsing m, Monad m) => Parsing (IdentityT m)
Parsing m => Parsing (Unlined m)
Parsing m => Parsing (Unspaced m)
Parsing m => Parsing (Unhighlighted m)
(Parsing m, MonadPlus m) => Parsing (ReaderT e m)
(Parsing m, MonadPlus m) => Parsing (StateT s m)
(Parsing m, MonadPlus m) => Parsing (StateT s m)
(Parsing m, MonadPlus m, Monoid w) => Parsing (WriterT w m)
(Parsing m, MonadPlus m, Monoid w) => Parsing (WriterT w m)
(Stream s m t, Show t) => Parsing (ParsecT s u m)
(Parsing m, MonadPlus m, Monoid w) => Parsing (RWST r w s m)
(Parsing m, MonadPlus m, Monoid w) => Parsing (RWST r w s m)