Copyright | © 2015–2016 Megaparsec contributors © 2007 Paolo Martini © 1999–2001 Daan Leijen |
---|---|
License | FreeBSD |
Maintainer | Mark Karpov <markkarpov@opmbx.org> |
Stability | experimental |
Portability | portable |
Safe Haskell | None |
Language | Haskell2010 |
This module includes everything you need to get started writing a parser.
By default this module is set up to parse character data. If you'd like to parse the result of your own tokenizer you should start with the following imports:
import Text.Megaparsec.Prim import Text.Megaparsec.Combinator
Then you can implement your own version of satisfy
on top of the
token
primitive.
Typical import section looks like this:
import Text.Megaparsec import Text.Megaparsec.String -- import Text.Megaparsec.ByteString -- import Text.Megaparsec.ByteString.Lazy -- import Text.Megaparsec.Text -- import Text.Megaparsec.Text.Lazy
As you can see the second import depends on data type you want to use as
input stream. It just defines useful type-synonym Parser
.
Megaparsec is capable of a lot. Apart from this standard functionality you can parse permutation phrases with Text.Megaparsec.Perm and even entire languages with Text.Megaparsec.Lexer. These modules should be imported explicitly along with the two modules mentioned above.
- type Parsec s = ParsecT s Identity
- data ParsecT s m a
- runParser :: Stream s t => Parsec s a -> String -> s -> Either ParseError a
- runParser' :: Stream s t => Parsec s a -> State s -> (State s, Either ParseError a)
- runParserT :: (Monad m, Stream s t) => ParsecT s m a -> String -> s -> m (Either ParseError a)
- runParserT' :: (Monad m, Stream s t) => ParsecT s m a -> State s -> m (State s, Either ParseError a)
- parse :: Stream s t => Parsec s a -> String -> s -> Either ParseError a
- parseMaybe :: Stream s t => Parsec s a -> s -> Maybe a
- parseTest :: (Stream s t, Show a) => Parsec s a -> s -> IO ()
- parseFromFile :: StorableStream s t => Parsec s a -> FilePath -> IO (Either ParseError a)
- (<|>) :: Alternative f => forall a. f a -> f a -> f a
- many :: Alternative f => forall a. f a -> f [a]
- some :: Alternative f => forall a. f a -> f [a]
- optional :: Alternative f => f a -> f (Maybe a)
- unexpected :: MonadParsec s m t => String -> m a
- failure :: MonadParsec s m t => [Message] -> m a
- (<?>) :: MonadParsec s m t => m a -> String -> m a
- label :: MonadParsec s m t => String -> m a -> m a
- hidden :: MonadParsec s m t => m a -> m a
- try :: MonadParsec s m t => m a -> m a
- lookAhead :: MonadParsec s m t => m a -> m a
- notFollowedBy :: MonadParsec s m t => m a -> m ()
- withRecovery :: MonadParsec s m t => (ParseError -> m a) -> m a -> m a
- eof :: MonadParsec s m t => m ()
- token :: MonadParsec s m t => (Int -> SourcePos -> t -> SourcePos) -> (t -> Either [Message] a) -> m a
- tokens :: (MonadParsec s m t, Eq t) => (Int -> SourcePos -> [t] -> SourcePos) -> (t -> t -> Bool) -> [t] -> m [t]
- between :: Applicative m => m open -> m close -> m a -> m a
- choice :: (Foldable f, Alternative m) => f (m a) -> m a
- count :: Applicative m => Int -> m a -> m [a]
- count' :: Alternative m => Int -> Int -> m a -> m [a]
- eitherP :: Alternative m => m a -> m b -> m (Either a b)
- endBy :: Alternative m => m a -> m sep -> m [a]
- endBy1 :: Alternative m => m a -> m sep -> m [a]
- manyTill :: Alternative m => m a -> m end -> m [a]
- someTill :: Alternative m => m a -> m end -> m [a]
- option :: Alternative m => a -> m a -> m a
- sepBy :: Alternative m => m a -> m sep -> m [a]
- sepBy1 :: Alternative m => m a -> m sep -> m [a]
- sepEndBy :: Alternative m => m a -> m sep -> m [a]
- sepEndBy1 :: Alternative m => m a -> m sep -> m [a]
- skipMany :: Alternative m => m a -> m ()
- skipSome :: Alternative m => m a -> m ()
- newline :: MonadParsec s m Char => m Char
- crlf :: MonadParsec s m Char => m String
- eol :: MonadParsec s m Char => m String
- tab :: MonadParsec s m Char => m Char
- space :: MonadParsec s m Char => m ()
- controlChar :: MonadParsec s m Char => m Char
- spaceChar :: MonadParsec s m Char => m Char
- upperChar :: MonadParsec s m Char => m Char
- lowerChar :: MonadParsec s m Char => m Char
- letterChar :: MonadParsec s m Char => m Char
- alphaNumChar :: MonadParsec s m Char => m Char
- printChar :: MonadParsec s m Char => m Char
- digitChar :: MonadParsec s m Char => m Char
- octDigitChar :: MonadParsec s m Char => m Char
- hexDigitChar :: MonadParsec s m Char => m Char
- markChar :: MonadParsec s m Char => m Char
- numberChar :: MonadParsec s m Char => m Char
- punctuationChar :: MonadParsec s m Char => m Char
- symbolChar :: MonadParsec s m Char => m Char
- separatorChar :: MonadParsec s m Char => m Char
- asciiChar :: MonadParsec s m Char => m Char
- latin1Char :: MonadParsec s m Char => m Char
- charCategory :: MonadParsec s m Char => GeneralCategory -> m Char
- char :: MonadParsec s m Char => Char -> m Char
- char' :: MonadParsec s m Char => Char -> m Char
- anyChar :: MonadParsec s m Char => m Char
- oneOf :: MonadParsec s m Char => String -> m Char
- oneOf' :: MonadParsec s m Char => String -> m Char
- noneOf :: MonadParsec s m Char => String -> m Char
- noneOf' :: MonadParsec s m Char => String -> m Char
- satisfy :: MonadParsec s m Char => (Char -> Bool) -> m Char
- string :: MonadParsec s m Char => String -> m String
- string' :: MonadParsec s m Char => String -> m String
- data Message
- messageString :: Message -> String
- badMessage :: Message -> Bool
- data ParseError
- errorPos :: ParseError -> SourcePos
- errorMessages :: ParseError -> [Message]
- errorIsUnknown :: ParseError -> Bool
- data SourcePos
- sourceName :: SourcePos -> String
- sourceLine :: SourcePos -> Int
- sourceColumn :: SourcePos -> Int
- class (ShowToken t, ShowToken [t]) => Stream s t | s -> t where
- class Stream s t => StorableStream s t where
- data State s = State {
- stateInput :: s
- statePos :: !SourcePos
- stateTabWidth :: !Int
- getInput :: MonadParsec s m t => m s
- setInput :: MonadParsec s m t => s -> m ()
- getPosition :: MonadParsec s m t => m SourcePos
- setPosition :: MonadParsec s m t => SourcePos -> m ()
- getTabWidth :: MonadParsec s m t => m Int
- setTabWidth :: MonadParsec s m t => Int -> m ()
- getParserState :: MonadParsec s m t => m (State s)
- setParserState :: MonadParsec s m t => State s -> m ()
- updateParserState :: MonadParsec s m t => (State s -> State s) -> m ()
Running parser
type Parsec s = ParsecT s Identity Source
Parsec
is non-transformer variant of more general ParsecT
monad transformer.
ParsecT s m a
is a parser with stream type s
, underlying monad m
and return type a
.
MonadError e m => MonadError e (ParsecT s m) Source | |
MonadReader r m => MonadReader r (ParsecT s m) Source | |
MonadState s m => MonadState s (ParsecT s' m) Source | |
Stream s t => MonadParsec s (ParsecT s m) t Source | |
MonadTrans (ParsecT s) Source | |
Monad (ParsecT s m) Source | |
Functor (ParsecT s m) Source | |
Applicative (ParsecT s m) Source | |
Alternative (ParsecT s m) Source | |
MonadPlus (ParsecT s m) Source | |
MonadFail (ParsecT s m) Source | |
MonadIO m => MonadIO (ParsecT s m) Source | |
MonadCont m => MonadCont (ParsecT s m) Source |
:: Stream s t | |
=> Parsec s a | Parser to run |
-> String | Name of source file |
-> s | Input for parser |
-> Either ParseError a |
runParser p file input
runs parser p
on the input list of tokens
input
, obtained from source file
. The file
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 file = runParser p file <$> readFile file
:: (Monad m, Stream s t) | |
=> ParsecT s m a | Parser to run |
-> String | Name of source file |
-> s | Input for parser |
-> m (Either ParseError a) |
runParserT p file input
runs parser p
on the input list of tokens
input
, obtained from source file
. The file
is only used in error
messages and may be the empty string. Returns a computation in the
underlying monad m
that returns either a ParseError
(Left
) or a
value of type a
(Right
).
:: (Monad m, Stream s t) | |
=> ParsecT s m a | Parser to run |
-> State s | Initial state |
-> m (State s, Either ParseError a) |
This function is similar to runParserT
, but like runParser'
it
accepts and returns parser state. This is thus the most general way to
run a parser.
Since: 4.2.0
:: Stream s t | |
=> Parsec s a | Parser to run |
-> String | Name of source file |
-> s | Input for parser |
-> Either ParseError a |
parse p file input
runs parser p
over Identity
(see runParserT
if you're using the ParsecT
monad transformer; parse
itself is just a
synonym for runParser
). It returns either a ParseError
(Left
) or a
value of type a
(Right
). show
or print
can be used to turn
ParseError
into the string representation of the error message. See
Text.Megaparsec.Error if you need to do more advanced error analysis.
main = case (parse numbers "" "11, 2, 43") of Left err -> print err Right xs -> print (sum xs) numbers = commaSep integer
parseMaybe :: Stream s t => Parsec s a -> s -> Maybe a Source
parseMaybe p input
runs parser p
on input
and returns result
inside Just
on success and Nothing
on failure. This function also
parses eof
, so if the parser doesn't consume all of its input, it will
fail.
The function is supposed to be useful for lightweight parsing, where error messages (and thus file name) are not important and entire input should be parsed. For example it can be used when parsing of single number according to specification of its format is desired.
parseTest :: (Stream s 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.
:: StorableStream s t | |
=> Parsec s a | Parser to run |
-> FilePath | Name of file to parse |
-> IO (Either ParseError a) |
parseFromFile p filename
runs parser p
on the input read from
filename
. 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
Combinators
(<|>) :: Alternative f => forall a. f a -> f a -> f a
An associative binary operation
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.
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.
many :: Alternative f => forall a. f a -> f [a]
Zero or more.
many p
applies the parser p
zero or more times. Returns a list of
the returned values of p
.
identifier = (:) <$> letter <*> many (alphaNum <|> char '_')
some :: Alternative f => forall a. f a -> f [a]
One or more.
some p
applies the parser p
one or more times. Returns a list of
the returned values of p
.
word = some letter
optional :: Alternative f => f a -> f (Maybe a)
One or none.
optional p
tries to apply parser p
. It will parse p
or nothing. It
only fails if p
fails after consuming input. On success result of p
is returned inside of Just
, on failure Nothing
is returned.
unexpected :: MonadParsec s m t => String -> m a Source
The parser unexpected msg
always fails with an unexpected error
message msg
without consuming any input.
The parsers fail
, label
and unexpected
are the three parsers used
to generate error messages. Of these, only label
is commonly used.
failure :: MonadParsec s m t => [Message] -> m a Source
The most general way to stop parsing and report ParseError
.
unexpected
is defined in terms of the function:
unexpected = failure . pure . Unexpected
Since: 4.2.0
(<?>) :: MonadParsec s m t => m a -> String -> m a infix 0 Source
A synonym for label
in form of an operator.
label :: MonadParsec s m t => String -> m a -> m a Source
The parser label name p
behaves as parser p
, but whenever the
parser p
fails without consuming any input, it replaces names of
“expected” tokens with the name name
.
hidden :: MonadParsec s m t => m a -> m a Source
hidden p
behaves just like parser p
, but it doesn't show any
“expected” tokens in error message when p
fails.
try :: MonadParsec s m t => m a -> 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.
For example, here is a parser that will try (sorry for the pun) to parse word “let” or “lexical”:
>>>
parseTest (string "let" <|> string "lexical") "lexical"
1:1: unexpected "lex" expecting "let"
What happens here? First parser consumes “le” and fails (because it
doesn't see a “t”). The second parser, however, isn't tried, since the
first parser has already consumed some input! try
fixes this
behavior and allows backtracking to work:
>>>
parseTest (try (string "let") <|> string "lexical") "lexical"
"lexical"
try
also improves error messages in case of overlapping alternatives,
because Megaparsec's hint system can be used:
>>>
parseTest (try (string "let") <|> string "lexical") "le"
1:1: unexpected "le" expecting "let" or "lexical"
Please note that as of Megaparsec 4.4.0, string
backtracks
automatically (see tokens
), so it does not need try
. However, the
examples above demonstrate the idea behind try
so well that it was
decided to keep them.
lookAhead :: MonadParsec s m t => m a -> 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.
notFollowedBy :: MonadParsec s m t => m a -> m () Source
notFollowedBy p
only succeeds when parser p
fails. This parser
does not consume any input and can be used to implement the “longest
match” rule.
:: MonadParsec s m t | |
=> (ParseError -> m a) | How to recover from failure |
-> m a | Original parser |
-> m a | Parser that can recover from failures |
withRecovery r p
allows continue parsing even if parser p
fails. In this case r
is called with actual ParseError
as its
argument. Typical usage is to return value signifying failure to parse
this particular object and to consume some part of input up to start of
next object.
Note that if r
fails, original error message is reported as if
without withRecovery
. In no way recovering parser r
can influence
error messages.
Since: 4.4.0
eof :: MonadParsec s m t => m () Source
This parser only succeeds at the end of the input.
:: MonadParsec s m t | |
=> (Int -> SourcePos -> t -> SourcePos) | Next position calculating function |
-> (t -> Either [Message] a) | Matching function for the token to parse |
-> m a |
The parser token nextPos testTok
accepts a token t
with result
x
when the function testTok t
returns
. The position of
the next token should be returned when Right
xnextPos
is called with the
tab width, current source position, and the current token.
This is the most primitive combinator for accepting tokens. For
example, the char
parser could be implemented
as:
char c = token updatePosChar testChar where testChar x = if x == c then Right x else Left . pure . Unexpected . showToken $ x
:: (MonadParsec s m t, Eq t) | |
=> (Int -> SourcePos -> [t] -> SourcePos) | Computes position of tokens |
-> (t -> t -> Bool) | Predicate to check equality of tokens |
-> [t] | List of tokens to parse |
-> m [t] |
The parser tokens posFromTok test
parses list of tokens and returns
it. posFromTok
is called with three arguments: tab width, initial
position, and collection of tokens to parse. The resulting parser will
use showToken
to pretty-print the collection of tokens in error
messages. Supplied predicate test
is used to check equality of given
and parsed tokens.
This can be used for example to write string
:
string = tokens updatePosString (==)
Note that beginning from Megaparsec 4.4.0, this is an auto-backtracking
primitive, which means that if it fails, it never consumes any
input. This is done to make its consumption model match how error
messages for this primitive are reported (which becomes an important
thing as user gets more control with primitives like withRecovery
):
>>>
parseTest (string "abc") "abd"
1:1: unexpected "abd" expecting "abc"
This means, in particular, that it's no longer necessary to use try
with tokens
-based parsers, such as string
and
string'
. This new feature does not affect
performance in any way.
between :: Applicative m => m open -> m close -> m a -> m a Source
between open close p
parses open
, followed by p
and close
.
Returns the value returned by p
.
braces = between (symbol "{") (symbol "}")
choice :: (Foldable f, Alternative m) => f (m a) -> m a Source
choice ps
tries to apply the parsers in the list ps
in order,
until one of them succeeds. Returns the value of the succeeding parser.
count :: Applicative m => Int -> m a -> m [a] Source
count n p
parses n
occurrences of p
. If n
is smaller or
equal to zero, the parser equals to return []
. Returns a list of n
values.
count' :: Alternative m => Int -> Int -> m a -> m [a] Source
count' m n p
parses from m
to n
occurrences of p
. If n
is
not positive or m > n
, the parser equals to return []
. Returns a list
of parsed values.
Please note that m
may be negative, in this case effect is the same
as if it were equal to zero.
eitherP :: Alternative m => m a -> m b -> m (Either a b) Source
Combine two alternatives.
Since: 4.4.0
endBy :: Alternative m => m a -> m sep -> m [a] Source
endBy p sep
parses zero or more occurrences of p
, separated
and ended by sep
. Returns a list of values returned by p
.
cStatements = cStatement `endBy` semicolon
endBy1 :: Alternative m => m a -> m sep -> m [a] Source
endBy1 p sep
parses one or more occurrences of p
, separated
and ended by sep
. Returns a list of values returned by p
.
manyTill :: Alternative m => m a -> m end -> m [a] Source
manyTill p end
applies parser p
zero or more times until
parser end
succeeds. Returns the list of values returned by p
. This
parser can be used to scan comments:
simpleComment = string "<!--" >> manyTill anyChar (string "-->")
someTill :: Alternative m => m a -> m end -> m [a] Source
someTill p end
works similarly to manyTill p end
, but p
should
succeed at least once.
option :: Alternative m => a -> m a -> m a Source
option x p
tries to apply parser p
. If p
fails without
consuming input, it returns the value x
, otherwise the value returned
by p
.
priority = option 0 (digitToInt <$> digitChar)
sepBy :: Alternative m => m a -> m sep -> m [a] Source
sepBy p sep
parses zero or more occurrences of p
, separated
by sep
. Returns a list of values returned by p
.
commaSep p = p `sepBy` comma
sepBy1 :: Alternative m => m a -> m sep -> m [a] Source
sepBy1 p sep
parses one or more occurrences of p
, separated
by sep
. Returns a list of values returned by p
.
sepEndBy :: Alternative m => m a -> m sep -> m [a] Source
sepEndBy p sep
parses zero or more occurrences of p
,
separated and optionally ended by sep
. Returns a list of values
returned by p
.
sepEndBy1 :: Alternative m => m a -> m sep -> m [a] Source
sepEndBy1 p sep
parses one or more occurrences of p
,
separated and optionally ended by sep
. Returns a list of values
returned by p
.
skipMany :: Alternative m => m a -> m () Source
skipMany p
applies the parser p
zero or more times, skipping
its result.
space = skipMany spaceChar
skipSome :: Alternative m => m a -> m () Source
skipSome p
applies the parser p
one or more times, skipping
its result.
Character parsing
newline :: MonadParsec s m Char => m Char Source
Parses a newline character.
crlf :: MonadParsec s m Char => m String Source
Parses a carriage return character followed by a newline character. Returns sequence of characters parsed.
eol :: MonadParsec s m Char => m String Source
tab :: MonadParsec s m Char => m Char Source
Parses a tab character.
space :: MonadParsec s m Char => m () Source
controlChar :: MonadParsec s m Char => m Char Source
Parses control characters, which are the non-printing characters of the Latin-1 subset of Unicode.
spaceChar :: MonadParsec s m Char => m Char Source
Parses a Unicode space character, and the control characters: tab, newline, carriage return, form feed, and vertical tab.
upperChar :: MonadParsec s m Char => m Char Source
Parses an upper-case or title-case alphabetic Unicode character. Title case is used by a small number of letter ligatures like the single-character form of Lj.
lowerChar :: MonadParsec s m Char => m Char Source
Parses a lower-case alphabetic Unicode character.
letterChar :: MonadParsec s m Char => m Char Source
Parses alphabetic Unicode characters: lower-case, upper-case and title-case letters, plus letters of case-less scripts and modifiers letters.
alphaNumChar :: MonadParsec s m Char => m Char Source
Parses alphabetic or numeric digit Unicode characters.
Note that numeric digits outside the ASCII range are parsed by this
parser but not by digitChar
. Such digits may be part of identifiers but
are not used by the printer and reader to represent numbers.
printChar :: MonadParsec s m Char => m Char Source
Parses printable Unicode characters: letters, numbers, marks, punctuation, symbols and spaces.
digitChar :: MonadParsec s m Char => m Char Source
Parses an ASCII digit, i.e between “0” and “9”.
octDigitChar :: MonadParsec s m Char => m Char Source
Parses an octal digit, i.e. between “0” and “7”.
hexDigitChar :: MonadParsec s m Char => m Char Source
Parses a hexadecimal digit, i.e. between “0” and “9”, or “a” and “f”, or “A” and “F”.
markChar :: MonadParsec s m Char => m Char Source
Parses Unicode mark characters, for example accents and the like, which combine with preceding characters.
numberChar :: MonadParsec s m Char => m Char Source
Parses Unicode numeric characters, including digits from various scripts, Roman numerals, et cetera.
punctuationChar :: MonadParsec s m Char => m Char Source
Parses Unicode punctuation characters, including various kinds of connectors, brackets and quotes.
symbolChar :: MonadParsec s m Char => m Char Source
Parses Unicode symbol characters, including mathematical and currency symbols.
separatorChar :: MonadParsec s m Char => m Char Source
Parses Unicode space and separator characters.
asciiChar :: MonadParsec s m Char => m Char Source
Parses a character from the first 128 characters of the Unicode character set, corresponding to the ASCII character set.
latin1Char :: MonadParsec s m Char => m Char Source
Parses a character from the first 256 characters of the Unicode character set, corresponding to the ISO 8859-1 (Latin-1) character set.
charCategory :: MonadParsec s m Char => GeneralCategory -> m Char Source
charCategory cat
Parses character in Unicode General Category cat
,
see GeneralCategory
.
char :: MonadParsec s m Char => Char -> m Char Source
char c
parses a single character c
.
semicolon = char ';'
char' :: MonadParsec s m Char => Char -> m Char Source
The same as char
but case-insensitive. This parser returns actually
parsed character preserving its case.
>>>
parseTest (char' 'e') "E"
'E'>>>
parseTest (char' 'e') "G"
1:1: unexpected 'G' expecting 'E' or 'e'
anyChar :: MonadParsec s m Char => m Char Source
This parser succeeds for any character. Returns the parsed character.
oneOf :: MonadParsec s m Char => String -> m Char Source
oneOf cs
succeeds if the current character is in the supplied
list of characters cs
. Returns the parsed character. Note that this
parser doesn't automatically generate “expected” component of error
message, so usually you should label it manually with label
or
(<?>
).
See also: satisfy
.
digit = oneOf ['0'..'9'] <?> "digit"
oneOf' :: MonadParsec s m Char => String -> m Char Source
The same as oneOf
, but case-insensitive. Returns the parsed character
preserving its case.
vowel = oneOf' "aeiou" <?> "vowel"
noneOf :: MonadParsec s m Char => String -> m Char Source
As the dual of oneOf
, noneOf cs
succeeds if the current
character not in the supplied list of characters cs
. Returns the
parsed character.
noneOf' :: MonadParsec s m Char => String -> m Char Source
The same as noneOf
, but case-insensitive.
consonant = noneOf' "aeiou" <?> "consonant"
satisfy :: MonadParsec s m Char => (Char -> Bool) -> m Char Source
The parser satisfy f
succeeds for any character for which the
supplied function f
returns True
. Returns the character that is
actually parsed.
digitChar = satisfy isDigit <?> "digit" oneOf cs = satisfy (`elem` cs)
string :: MonadParsec s m Char => String -> m String Source
string s
parses a sequence of characters given by s
. Returns
the parsed string (i.e. s
).
divOrMod = string "div" <|> string "mod"
string' :: MonadParsec s m Char => String -> m String Source
The same as string
, but case-insensitive. On success returns string
cased as actually parsed input.
>>>
parseTest (string' "foobar") "foObAr"
"foObAr"
Error messages
This data type represents parse error messages.
messageString :: Message -> String Source
Extract the message string from an error message.
badMessage :: Message -> Bool Source
Test if message string is empty.
data ParseError Source
errorPos :: ParseError -> SourcePos Source
Extract the source position from ParseError
.
errorMessages :: ParseError -> [Message] Source
Extract the list of error messages from ParseError
.
errorIsUnknown :: ParseError -> Bool Source
Test whether given ParseError
has associated collection of error
messages. Return True
if it has none and False
otherwise.
Textual source position
sourceName :: SourcePos -> String Source
Extract the name of the source from a source position.
sourceLine :: SourcePos -> Int Source
Extract the line number from a source position.
sourceColumn :: SourcePos -> Int Source
Extract the column number from a source position.
Low-level operations
class (ShowToken t, ShowToken [t]) => Stream s t | s -> t where Source
An instance of Stream s t
has stream type s
, and token type t
determined by the stream.
class Stream s t => StorableStream s t where Source
StorableStream
abstracts ability of some streams to be stored in a
file. This is used by the polymorphic function parseFromFile
.
This is Megaparsec state, it's parametrized over stream type s
.
State | |
|
getInput :: MonadParsec s m t => m s Source
Returns the current input.
setInput :: MonadParsec s m t => s -> m () Source
setInput input
continues parsing with input
. The getInput
and
setInput
functions can for example be used to deal with #include files.
getPosition :: MonadParsec s m t => m SourcePos Source
Returns the current source position.
See also: SourcePos
.
setPosition :: MonadParsec s m t => SourcePos -> m () Source
setPosition pos
sets the current source position to pos
.
getTabWidth :: MonadParsec s m t => m Int Source
Returns tab width. Default tab width is equal to defaultTabWidth
. You
can set different tab width with help of setTabWidth
.
setTabWidth :: MonadParsec s m t => Int -> m () Source
Set tab width. If argument of the function is not positive number,
defaultTabWidth
will be used.
getParserState :: MonadParsec s m t => m (State s) Source
Returns the full parser state as a State
record.
setParserState :: MonadParsec s m t => State s -> m () Source
setParserState st
set the full parser state to st
.
updateParserState :: MonadParsec s m t => (State s -> State s) -> m () Source
updateParserState f
applies function f
to the parser state.