parsec-3.1.3: Monadic parser combinators

Portability | portable
Stability | provisional
Maintainer | derek.a.elkins@gmail.com
Safe Haskell | Safe-Inferred

Text.Parsec.Prim

Description

The primitive parser combinators.

Synopsis

- 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
  - = Consumed a
  - | Empty !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
- lookAhead :: Stream s m t => ParsecT s u m a -> ParsecT s u m a
- class Monad m => Stream s m t | s -> t where
  - uncons :: s -> m (Maybe (t, s))
- 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 -> ParseError Source

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 `notFollowedBy`.

data ParsecT s u m a Source

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.

Instances

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.

type Parsec s u = ParsecT s u Identity Source

data Consumed a Source

Constructors

Consumed a |
Empty !a |

Instances

Functor Consumed |

data Reply s u a Source

Constructors

Ok a !(State s u) ParseError |
Error ParseError |

Instances

Functor (Reply s u) |

data State s u Source

Constructors

State |
Fields stateInput :: s statePos :: !SourcePos stateUser :: !u

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

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

`parserZero` always fails without consuming any input. `parserZero` is defined equal to the `mzero` member of the `MonadPlus` class and to the `empty` member of the `Applicative` class.

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 (`<|>`) member of `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.

label :: ParsecT s u m a -> String -> ParsecT s u m aSource

labels :: ParsecT s u m a -> [String] -> ParsecT s u m aSource

lookAhead :: Stream s m t => ParsecT s u m a -> ParsecT s u m aSource

`lookAhead p` parses `p` without consuming any input.

If `p` fails and consumes some input, so does `lookAhead`. Combine with `try` if this is undesirable.

class Monad m => Stream s m t | s -> t where Source

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.

Methods

uncons :: s -> m (Maybe (t, s))Source

Instances

Monad m => Stream ByteString m Char |
Monad m => Stream ByteString m Char |
Monad m => Stream Text m Char |
Monad m => Stream Text 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

token Source

Arguments

:: 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 ``Just` x`. The source position of the `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

tokenPrim Source

Arguments

:: 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 `tokenPrim showTok nextPos testTok` accepts a token `t` with result `x` when the function `testTok t` returns ``Just` x`. The token can be shown using `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 `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

manyAccum :: (a -> [a] -> [a]) -> ParsecT s u m a -> ParsecT s u m [a]Source

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 SourcePos Source

Returns the current source position. See also `SourcePos`.

getInput :: Monad m => ParsecT s u m sSource

Returns the current input

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.

getState :: Monad m => ParsecT s u m uSource

Returns the current user state.

putState :: Monad m => u -> ParsecT s u m ()Source

`putState st` set the user state to `st`.

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.