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
- runParsecT :: Monad m => ParsecT s u m a -> State s u -> m (Consumed (m (Reply s u a)))
- mkPT :: Monad m => (State s u -> m (Consumed (m (Reply s u a)))) -> ParsecT s u m 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 :: (a -> b) -> ParsecT s u m a -> ParsecT s u m b
- parserReturn :: a -> ParsecT s u m a
- parserBind :: 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 :: String -> ParsecT s u m a
- parserZero :: ParsecT s u m a
- parserPlus :: ParsecT s u m a -> ParsecT s u m a -> ParsecT s u m a
- (<?>) :: ParsecT s u m a -> String -> ParsecT s u m a
- (<|>) :: ParsecT s u m a -> ParsecT s u m a -> ParsecT s u m a
- label :: ParsecT s u m a -> String -> ParsecT s u m a
- labels :: 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 :: 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 :: ParsecT s u m a -> ParsecT s u m [a]
- skipMany :: ParsecT s u m a -> ParsecT s u m ()
- manyAccum :: (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 :: (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.

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 (ParsecT s u m) | |

Functor (ParsecT s u m) | |

MonadPlus (ParsecT s u m) | |

Applicative (ParsecT s u m) | |

Alternative (ParsecT s u m) | |

MonadIO m => MonadIO (ParsecT s u m) | |

MonadCont m => MonadCont (ParsecT s u m) |

runParsecT :: Monad m => ParsecT s u m a -> State s u -> m (Consumed (m (Reply s u a)))Source

Low-level unpacking of the ParsecT type. To run your parser, please look to runPT, runP, runParserT, runParser and other such functions.

mkPT :: Monad m => (State s u -> m (Consumed (m (Reply s u a)))) -> ParsecT s u m aSource

Low-level creation of the ParsecT type. You really shouldn't have to do this.

parserReturn :: a -> ParsecT s u m aSource

parserBind :: ParsecT s u m a -> (a -> ParsecT s u m b) -> ParsecT s u m bSource

mergeErrorReply :: ParseError -> Reply s u a -> Reply s u aSource

parserFail :: String -> ParsecT s u m aSource

parserZero :: ParsecT s u m aSource

parserPlus :: ParsecT s u m a -> ParsecT s u m a -> ParsecT s u m aSource

(<?>) :: 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.

(<|>) :: 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 state`s`

. 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 :: 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 `tokenPrim showTok posFromTok testTok`

accepts a token `t`

with result `x`

when the function `testTok t`

returns

. The
source position of the `Just`

x`t`

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`

x`showTok 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 :: 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 :: 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 :: (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.