Portability | portable |
---|---|
Stability | provisional |
Maintainer | derek.a.elkins@gmail.com |
The primitive parser combinators.
- unknownError :: State s u -> ParseError
- sysUnExpectError :: String -> SourcePos -> Reply s u a
- unexpected :: Stream s m t => String -> ParsecT s u m a
- data ParsecT s u m a = ParsecT {
- runParsecT :: State s u -> m (Consumed (m (Reply s u a)))
- type Parsec s u = ParsecT s u Identity
- data Consumed a
- data Reply s u a
- = Ok a !(State s u) ParseError
- | Error ParseError
- data State s u = State {
- stateInput :: s
- statePos :: !SourcePos
- stateUser :: !u
- parsecMap :: Monad m => (a -> b) -> ParsecT s u m a -> ParsecT s u m b
- parserReturn :: Monad m => a -> ParsecT s u m a
- parserBind :: Monad m => ParsecT s u m a -> (a -> ParsecT s u m b) -> ParsecT s u m b
- mergeErrorReply :: ParseError -> Reply s u a -> Reply s u a
- parserFail :: Monad m => String -> ParsecT s u m a
- parserZero :: Monad m => ParsecT s u m a
- parserPlus :: Monad m => ParsecT s u m a -> ParsecT s u m a -> ParsecT s u m a
- (<?>) :: Monad m => ParsecT s u m a -> String -> ParsecT s u m a
- (<|>) :: Monad m => ParsecT s u m a -> ParsecT s u m a -> ParsecT s u m a
- label :: Monad m => ParsecT s u m a -> String -> ParsecT s u m a
- labels :: Monad m => ParsecT s u m a -> [String] -> ParsecT s u m a
- class Monad m => Stream s m t | s -> t where
- tokens :: (Stream s m t, Eq t) => ([t] -> String) -> (SourcePos -> [t] -> SourcePos) -> [t] -> ParsecT s u m [t]
- try :: Stream s m t => ParsecT s u m a -> ParsecT s u m a
- token :: Stream s Identity t => (t -> String) -> (t -> SourcePos) -> (t -> Maybe a) -> Parsec s u a
- tokenPrim :: Stream s m t => (t -> String) -> (SourcePos -> t -> s -> SourcePos) -> (t -> Maybe a) -> ParsecT s u m a
- tokenPrimEx :: Stream s m t => (t -> String) -> (SourcePos -> t -> s -> SourcePos) -> Maybe (SourcePos -> t -> s -> u -> u) -> (t -> Maybe a) -> ParsecT s u m a
- many :: Stream s m t => ParsecT s u m a -> ParsecT s u m [a]
- skipMany :: Stream s m t => ParsecT s u m a -> ParsecT s u m ()
- manyAccum :: Stream s m t => (a -> [a] -> [a]) -> ParsecT s u m a -> ParsecT s u m [a]
- runPT :: Stream s m t => ParsecT s u m a -> u -> SourceName -> s -> m (Either ParseError a)
- runP :: Stream s Identity t => Parsec s u a -> u -> SourceName -> s -> Either ParseError a
- runParserT :: Stream s m t => ParsecT s u m a -> u -> SourceName -> s -> m (Either ParseError a)
- runParser :: Stream s Identity t => Parsec s u a -> u -> SourceName -> s -> Either ParseError a
- parse :: Stream s Identity t => Parsec s () a -> SourceName -> s -> Either ParseError a
- parseTest :: (Stream s Identity t, Show a) => Parsec s () a -> s -> IO ()
- getPosition :: Monad m => ParsecT s u m SourcePos
- getInput :: Monad m => ParsecT s u m s
- setPosition :: Monad m => SourcePos -> ParsecT s u m ()
- setInput :: Monad m => s -> ParsecT s u m ()
- getParserState :: Monad m => ParsecT s u m (State s u)
- setParserState :: Monad m => State s u -> ParsecT s u m (State s u)
- updateParserState :: Monad m => (State s u -> State s u) -> ParsecT s u m (State s u)
- getState :: Monad m => ParsecT s u m u
- putState :: Monad m => u -> ParsecT s u m ()
- modifyState :: Monad m => (u -> u) -> ParsecT s u m ()
- setState :: Monad m => u -> ParsecT s u m ()
- updateState :: Monad m => (u -> u) -> ParsecT s u m ()
Documentation
unknownError :: State s u -> ParseErrorSource
sysUnExpectError :: String -> SourcePos -> Reply s u aSource
unexpected :: Stream s m t => String -> ParsecT s u m aSource
The parser unexpected msg
always fails with an unexpected error
message msg
without consuming any input.
The parsers fail
, (<?>
) and unexpected
are the three parsers
used to generate error messages. Of these, only (<?>
) is commonly
used. For an example of the use of unexpected
, see the definition
of Text.Parsec.Combinator.notFollowedBy
.
ParserT monad transformer and Parser type
ParsecT s u m a
is a parser with stream type s
, user state type u
,
underlying monad m
and return type a
. Parsec is strict in the user state.
If this is undesirable, simply used a data type like data Box a = Box a
and
the state type Box YourStateType
to add a level of indirection.
ParsecT | |
|
MonadError e m => MonadError e (ParsecT s u m) | |
MonadReader r m => MonadReader r (ParsecT s u m) | |
MonadState s m => MonadState s (ParsecT s' u m) | |
MonadTrans (ParsecT s u) | |
Monad m => Monad (ParsecT s u m) | |
Monad m => Functor (ParsecT s u m) | |
Monad m => MonadPlus (ParsecT s u m) | |
Monad m => Applicative (ParsecT s u m) | |
Monad m => Alternative (ParsecT s u m) | |
MonadIO m => MonadIO (ParsecT s u m) | |
MonadCont m => MonadCont (ParsecT s u m) |
parserReturn :: Monad m => a -> ParsecT s u m aSource
mergeErrorReply :: ParseError -> Reply s u a -> Reply s u aSource
parserFail :: Monad m => String -> ParsecT s u m aSource
parserZero :: Monad m => ParsecT s u m aSource
(<?>) :: Monad m => ParsecT s u m a -> String -> ParsecT s u m aSource
The parser p ? msg
behaves as parser p
, but whenever the
parser p
fails without consuming any input, it replaces expect
error messages with the expect error message msg
.
This is normally used at the end of a set alternatives where we want
to return an error message in terms of a higher level construct
rather than returning all possible characters. For example, if the
expr
parser from the try
example would fail, the error
message is: '...: expecting expression'. Without the (<?>)
combinator, the message would be like '...: expecting "let" or
letter', which is less friendly.
(<|>) :: Monad m => ParsecT s u m a -> ParsecT s u m a -> ParsecT s u m aSource
This combinator implements choice. The parser p <|> q
first
applies p
. If it succeeds, the value of p
is returned. If p
fails without consuming any input, parser q
is tried. This
combinator is defined equal to the mplus
member of the MonadPlus
class and the (Control.Applicative.<|>
) member of Control.Applicative.Alternative
.
The parser is called predictive since q
is only tried when
parser p
didn't consume any input (i.e.. the look ahead is 1).
This non-backtracking behaviour allows for both an efficient
implementation of the parser combinators and the generation of good
error messages.
class Monad m => Stream s m t | s -> t whereSource
An instance of Stream
has stream type s
, underlying monad m
and token type t
determined by the stream
Some rough guidelines for a "correct" instance of Stream:
- unfoldM uncons gives the [t] corresponding to the stream
- A
Stream
instance is responsible for maintaining the "position within the stream" in the stream states
. This is trivial unless you are using the monad in a non-trivial way.
Monad m => Stream ByteString m Char | |
Monad m => Stream ByteString m Char | |
Monad m => Stream [tok] m tok |
tokens :: (Stream s m t, Eq t) => ([t] -> String) -> (SourcePos -> [t] -> SourcePos) -> [t] -> ParsecT s u m [t]Source
try :: Stream s m t => ParsecT s u m a -> ParsecT s u m aSource
The parser try p
behaves like parser p
, except that it
pretends that it hasn't consumed any input when an error occurs.
This combinator is used whenever arbitrary look ahead is needed.
Since it pretends that it hasn't consumed any input when p
fails,
the (<|>
) combinator will try its second alternative even when the
first parser failed while consuming input.
The try
combinator can for example be used to distinguish
identifiers and reserved words. Both reserved words and identifiers
are a sequence of letters. Whenever we expect a certain reserved
word where we can also expect an identifier we have to use the try
combinator. Suppose we write:
expr = letExpr <|> identifier <?> "expression" letExpr = do{ string "let"; ... } identifier = many1 letter
If the user writes "lexical", the parser fails with: unexpected
'x', expecting 't' in "let"
. Indeed, since the (<|>
) combinator
only tries alternatives when the first alternative hasn't consumed
input, the identifier
parser is never tried (because the prefix
"le" of the string "let"
parser is already consumed). The
right behaviour can be obtained by adding the try
combinator:
expr = letExpr <|> identifier <?> "expression" letExpr = do{ try (string "let"); ... } identifier = many1 letter
:: Stream s Identity t | |
=> (t -> String) | Token pretty-printing function. |
-> (t -> SourcePos) | Computes the position of a token. |
-> (t -> Maybe a) | Matching function for the token to parse. |
-> Parsec s u a |
The parser token showTok posFromTok testTok
accepts a token t
with result x
when the function testTok t
returns
. The
source position of the Just
xt
should be returned by posFromTok t
and
the token can be shown using showTok t
.
This combinator is expressed in terms of tokenPrim
.
It is used to accept user defined token streams. For example,
suppose that we have a stream of basic tokens tupled with source
positions. We can than define a parser that accepts single tokens as:
mytoken x = token showTok posFromTok testTok where showTok (pos,t) = show t posFromTok (pos,t) = pos testTok (pos,t) = if x == t then Just t else Nothing
:: Stream s m t | |
=> (t -> String) | Token pretty-printing function. |
-> (SourcePos -> t -> s -> SourcePos) | Next position calculating function. |
-> (t -> Maybe a) | Matching function for the token to parse. |
-> ParsecT s u m a |
The parser token showTok nextPos testTok
accepts a token t
with result x
when the function testTok t
returns
. The
token can be shown using Just
xshowTok t
. The position of the next
token should be returned when nextPos
is called with the current
source position pos
, the current token t
and the rest of the
tokens toks
, nextPos pos t toks
.
This is the most primitive combinator for accepting tokens. For
example, the Text.Parsec.Char.char
parser could be implemented as:
char c = tokenPrim showChar nextPos testChar where showChar x = "'" ++ x ++ "'" testChar x = if x == c then Just x else Nothing nextPos pos x xs = updatePosChar pos x
tokenPrimEx :: Stream s m t => (t -> String) -> (SourcePos -> t -> s -> SourcePos) -> Maybe (SourcePos -> t -> s -> u -> u) -> (t -> Maybe a) -> ParsecT s u m aSource
many :: Stream s m t => ParsecT s u m a -> ParsecT s u m [a]Source
many p
applies the parser p
zero or more times. Returns a
list of the returned values of p
.
identifier = do{ c <- letter ; cs <- many (alphaNum <|> char '_') ; return (c:cs) }
skipMany :: Stream s m t => ParsecT s u m a -> ParsecT s u m ()Source
skipMany p
applies the parser p
zero or more times, skipping
its result.
spaces = skipMany space
runPT :: Stream s m t => ParsecT s u m a -> u -> SourceName -> s -> m (Either ParseError a)Source
runP :: Stream s Identity t => Parsec s u a -> u -> SourceName -> s -> Either ParseError aSource
runParserT :: Stream s m t => ParsecT s u m a -> u -> SourceName -> s -> m (Either ParseError a)Source
The most general way to run a parser. runParserT p state filePath
input
runs parser p
on the input list of tokens input
,
obtained from source filePath
with the initial user state st
.
The filePath
is only used in error messages and may be the empty
string. Returns a computation in the underlying monad m
that return either a ParseError
(Left
) or a
value of type a
(Right
).
runParser :: Stream s Identity t => Parsec s u a -> u -> SourceName -> s -> Either ParseError aSource
The most general way to run a parser over the Identity monad. runParser p state filePath
input
runs parser p
on the input list of tokens input
,
obtained from source filePath
with the initial user state st
.
The filePath
is only used in error messages and may be the empty
string. Returns either a ParseError
(Left
) or a
value of type a
(Right
).
parseFromFile p fname = do{ input <- readFile fname ; return (runParser p () fname input) }
parse :: Stream s Identity t => Parsec s () a -> SourceName -> s -> Either ParseError aSource
parse p filePath input
runs a parser p
over Identity without user
state. The filePath
is only used in error messages and may be the
empty string. Returns either a ParseError
(Left
)
or a value of type a
(Right
).
main = case (parse numbers "" "11, 2, 43") of Left err -> print err Right xs -> print (sum xs) numbers = commaSep integer
parseTest :: (Stream s Identity t, Show a) => Parsec s () a -> s -> IO ()Source
The expression parseTest p input
applies a parser p
against
input input
and prints the result to stdout. Used for testing
parsers.
getPosition :: Monad m => ParsecT s u m SourcePosSource
Returns the current source position. See also SourcePos
.
setPosition :: Monad m => SourcePos -> ParsecT s u m ()Source
setPosition pos
sets the current source position to pos
.
setInput :: Monad m => s -> ParsecT s u m ()Source
setInput input
continues parsing with input
. The getInput
and
setInput
functions can for example be used to deal with #include
files.
getParserState :: Monad m => ParsecT s u m (State s u)Source
Returns the full parser state as a State
record.
setParserState :: Monad m => State s u -> ParsecT s u m (State s u)Source
setParserState st
set the full parser state to st
.
updateParserState :: Monad m => (State s u -> State s u) -> ParsecT s u m (State s u)Source
updateParserState f
applies function f
to the parser state.
modifyState :: Monad m => (u -> u) -> ParsecT s u m ()Source
updateState f
applies function f
to the user state. Suppose
that we want to count identifiers in a source, we could use the user
state as:
expr = do{ x <- identifier ; updateState (+1) ; return (Id x) }
setState :: Monad m => u -> ParsecT s u m ()Source
An alias for putState for backwards compatibility.
updateState :: Monad m => (u -> u) -> ParsecT s u m ()Source
An alias for modifyState for backwards compatibility.