|
Text.Parsec.Combinator | Portability | portable | Stability | provisional | Maintainer | derek.a.elkins@gmail.com |
|
|
|
Description |
Commonly used generic combinators
|
|
Synopsis |
|
|
|
Documentation |
|
|
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 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 open close p parses open, followed by p and close.
Returns the value returned by p.
braces = between (symbol "{") (symbol "}")
|
|
|
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)
})
|
|
|
option 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 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 p applies the parser p one or more times, skipping
its result.
|
|
|
many p applies the parser p one or more times. Returns a
list of the returned values of p.
word = many1 letter
|
|
|
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 p sep parses one or more occurrences of p, separated
by sep. Returns a list of values returned by p.
|
|
|
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
|
|
|
endBy1 p sep parses one or more occurrences of p, seperated
and ended by sep. Returns a list of values returned by p.
|
|
|
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 p sep parses one or more occurrences of p,
separated and optionally ended by sep. Returns a list of values
returned by p.
|
|
|
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.
|
|
|
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` mulop
term = factor `chainl1` addop
factor = parens expr <|> integer
mulop = do{ symbol "*"; return (*) }
<|> do{ symbol "/"; return (div) }
addop = do{ symbol "+"; return (+) }
<|> do{ symbol "-"; return (-) }
|
|
|
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.
|
|
|
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.
|
|
|
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 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
})
|
|
|
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 p parses p without consuming any input.
|
|
|
The parser anyToken accepts any kind of token. It is for example
used to implement eof. Returns the accepted token.
|
|
Produced by Haddock version 2.6.0 |