Copyright  (c) Daan Leijen 19992001 (c) Paolo Martini 2007 

License  BSDstyle (see the LICENSE file) 
Maintainer  [email protected] 
Stability  provisional 
Portability  portable 
Safe Haskell  Safe 
Language  Haskell2010 
The primitive parser combinators.
unknownError :: State s u > ParseError Source
sysUnExpectError :: String > SourcePos > Reply s u a Source
unexpected :: Stream s m t => String > ParsecT s u m a Source
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
.
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 use a data type like data Box a = Box a
and the state type Box YourStateType
to add a level of indirection.
MonadState s m => MonadState s (ParsecT s' u m)  
MonadReader r m => MonadReader r (ParsecT s u m)  
MonadError e m => MonadError e (ParsecT s u m)  
Defined in Text.Parsec.Prim MethodsthrowError :: e > ParsecT s u m a Source catchError :: ParsecT s u m a > (e > ParsecT s u m a) > ParsecT s u m a Source  
MonadTrans (ParsecT s u)  
Defined in Text.Parsec.Prim  
Monad (ParsecT s u m)  
Functor (ParsecT s u m)  
MonadFail (ParsecT s u m)  Since: parsec3.1.12.0 
Defined in Text.Parsec.Prim  
Applicative (ParsecT s u m)  
Defined in Text.Parsec.Prim Methodspure :: a > ParsecT s u m a Source (<*>) :: ParsecT s u m (a > b) > ParsecT s u m a > ParsecT s u m b Source liftA2 :: (a > b > c) > ParsecT s u m a > ParsecT s u m b > ParsecT s u m c Source (*>) :: ParsecT s u m a > ParsecT s u m b > ParsecT s u m b Source (<*) :: ParsecT s u m a > ParsecT s u m b > ParsecT s u m a Source  
MonadIO m => MonadIO (ParsecT s u m)  
Defined in Text.Parsec.Prim  
Alternative (ParsecT s u m)  
MonadPlus (ParsecT s u m)  
MonadCont m => MonadCont (ParsecT s u m)  
Semigroup a => Semigroup (ParsecT s u m a) 
The (many $ char a) <> (many $ char b) The above will parse a string like (many $ char a) >> (many $ char b) (many $ char a) *> (many $ char b) Since: parsec3.1.12 
(Monoid a, Semigroup (ParsecT s u m a)) => Monoid (ParsecT s u m a) 
The Since: parsec3.1.12 
runParsecT :: Monad m => ParsecT s u m a > State s u > m (Consumed (m (Reply s u a))) Source
Lowlevel 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 a Source
Lowlevel creation of the ParsecT type. You really shouldn't have to do this.
type Parsec s u = ParsecT s u Identity Source
Ok a !(State s u) ParseError  
Error ParseError 
State  
Fields

parsecMap :: (a > b) > ParsecT s u m a > ParsecT s u m b Source
parserReturn :: a > ParsecT s u m a Source
parserBind :: ParsecT s u m a > (a > ParsecT s u m b) > ParsecT s u m b Source
mergeErrorReply :: ParseError > Reply s u a > Reply s u a Source
parserFail :: String > ParsecT s u m a Source
parserZero :: ParsecT s u m a Source
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 Alternative
class.
parserPlus :: ParsecT s u m a > ParsecT s u m a > ParsecT s u m a Source
(<?>) :: ParsecT s u m a > String > ParsecT s u m a infix 0 Source
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 a infixr 1 Source
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 nonbacktracking 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 a Source
A synonym for <?>
, but as a function instead of an operator.
labels :: ParsecT s u m a > [String] > ParsecT s u m a Source
lookAhead :: Stream s m t => ParsecT s u m a > ParsecT s u m a Source
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:
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 nontrivial way.Monad m => Stream ByteString m Char  
Defined in Text.Parsec.Prim Methodsuncons :: ByteString > m (Maybe (Char, ByteString)) Source  
Monad m => Stream ByteString m Char  
Defined in Text.Parsec.Prim Methodsuncons :: ByteString > m (Maybe (Char, ByteString)) Source  
Monad m => Stream Text m Char  
Monad m => Stream Text m Char  
Monad m => Stream [tok] m tok  
Defined in Text.Parsec.Prim 
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 a Source
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 prettyprinting 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 then 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 prettyprinting 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 a Source
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 a Source
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 a Source
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 a Source
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 s Source
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 u Source
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
modifyState 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 ; modifyState (+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.
© The University of Glasgow and others
Licensed under a BSDstyle license (see top of the page).
https://downloads.haskell.org/~ghc/8.8.3/docs/html/libraries/parsec3.1.14.0/TextParsecPrim.html