Copyright  (c) Paolo Martini 2007 

License  BSDstyle (see the LICENSE file) 
Maintainer  [email protected] 
Stability  provisional 
Portability  portable 
Safe Haskell  Safe 
Language  Haskell2010 
Parsec compatibility module
(<?>) :: 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.
type Parser = Parsec String () Source
type GenParser tok st = Parsec [tok] st Source
runParser :: GenParser tok st a > st > SourceName > [tok] > Either ParseError a Source
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
parseFromFile :: Parser a > String > IO (Either ParseError a) Source
parseFromFile p filePath
runs a string parser p
on the input read from filePath
using readFile
. Returns either a ParseError
(Left
) or a value of type a
(Right
).
main = do{ result < parseFromFile numbers "digits.txt" ; case result of Left err > print err Right xs > print (sum xs) }
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.
:: 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
tokens :: (Stream s m t, Eq t) => ([t] > String) > (SourcePos > [t] > SourcePos) > [t] > ParsecT s u m [t] Source
:: 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
try :: GenParser tok st a > GenParser tok st a Source
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
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
.
pzero :: GenParser tok st 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
getState :: Monad m => ParsecT s u m u Source
Returns the current user state.
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.
getPosition :: Monad m => ParsecT s u m SourcePos Source
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
.
getInput :: Monad m => ParsecT s u m s Source
Returns the current input
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.
State  
Fields

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
.
© The University of Glasgow and others
Licensed under a BSDstyle license (see top of the page).
https://downloads.haskell.org/~ghc/8.6.1/docs/html/libraries/parsec3.1.13.0/TextParserCombinatorsParsecPrim.html