-- | -- Module : Text.Megaparsec.Char.Lexer -- Copyright : © 2015–2018 Megaparsec contributors -- © 2007 Paolo Martini -- © 1999–2001 Daan Leijen -- License : FreeBSD -- -- Maintainer : Mark Karpov <markkarpov92@gmail.com> -- Stability : experimental -- Portability : non-portable -- -- High-level parsers to help you write your lexer. The module doesn't -- impose how you should write your parser, but certain approaches may be -- more elegant than others. Especially important theme is parsing of white -- space, comments, and indentation. -- -- Parsing of white space is an important part of any parser. We propose a -- convention where __every lexeme parser assumes no spaces before the__ -- __lexeme and consumes all spaces after the lexeme__; this is what the -- 'lexeme' combinator does, and so it's enough to wrap every lexeme parser -- with 'lexeme' to achieve this. Note that you'll need to call 'space' -- manually to consume any white space before the first lexeme (i.e. at the -- beginning of the file). -- -- This module is intended to be imported qualified: -- -- > import qualified Text.Megaparsec.Char.Lexer as L -- -- To do lexing of byte streams, see "Text.Megaparsec.Byte.Lexer". {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE MultiWayIf #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE TypeFamilies #-} module Text.Megaparsec.Char.Lexer ( -- * White space space , lexeme , symbol , symbol' , skipLineComment , skipBlockComment , skipBlockCommentNested -- * Indentation , indentLevel , incorrectIndent , indentGuard , nonIndented , IndentOpt (..) , indentBlock , lineFold -- * Character and string literals , charLiteral -- * Numbers , decimal , binary , octal , hexadecimal , scientific , float , signed ) where import Control.Applicative import Control.Monad (void) import Data.List (foldl') import Data.List.NonEmpty (NonEmpty (..)) import Data.Maybe (listToMaybe, fromMaybe, isJust) import Data.Proxy import Data.Scientific (Scientific) import Text.Megaparsec import Text.Megaparsec.Lexer import qualified Data.Char as Char import qualified Data.Scientific as Sci import qualified Data.Set as E import qualified Text.Megaparsec.Char as C ---------------------------------------------------------------------------- -- White space -- | Given comment prefix this function returns a parser that skips line -- comments. Note that it stops just before the newline character but -- doesn't consume the newline. Newline is either supposed to be consumed by -- 'space' parser or picked up manually. skipLineComment :: (MonadParsec e s m, Token s ~ Char) => Tokens s -- ^ Line comment prefix -> m () skipLineComment prefix = C.string prefix *> void (takeWhileP (Just "character") (/= '\n')) {-# INLINEABLE skipLineComment #-} -- | @'skipBlockComment' start end@ skips non-nested block comment starting -- with @start@ and ending with @end@. skipBlockComment :: (MonadParsec e s m, Token s ~ Char) => Tokens s -- ^ Start of block comment -> Tokens s -- ^ End of block comment -> m () skipBlockComment start end = p >> void (manyTill anySingle n) where p = C.string start n = C.string end {-# INLINEABLE skipBlockComment #-} -- | @'skipBlockCommentNested' start end@ skips possibly nested block -- comment starting with @start@ and ending with @end@. -- -- @since 5.0.0 skipBlockCommentNested :: (MonadParsec e s m, Token s ~ Char) => Tokens s -- ^ Start of block comment -> Tokens s -- ^ End of block comment -> m () skipBlockCommentNested start end = p >> void (manyTill e n) where e = skipBlockCommentNested start end <|> void anySingle p = C.string start n = C.string end {-# INLINEABLE skipBlockCommentNested #-} ---------------------------------------------------------------------------- -- Indentation -- | Return the current indentation level. -- -- The function is a simple shortcut defined as: -- -- > indentLevel = sourceColumn <$> getPosition -- -- @since 4.3.0 indentLevel :: MonadParsec e s m => m Pos indentLevel = sourceColumn <$> getSourcePos {-# INLINE indentLevel #-} -- | Fail reporting incorrect indentation error. The error has attached -- information: -- -- * Desired ordering between reference level and actual level -- * Reference indentation level -- * Actual indentation level -- -- @since 5.0.0 incorrectIndent :: MonadParsec e s m => Ordering -- ^ Desired ordering between reference level and actual level -> Pos -- ^ Reference indentation level -> Pos -- ^ Actual indentation level -> m a incorrectIndent ord ref actual = fancyFailure . E.singleton $ ErrorIndentation ord ref actual {-# INLINEABLE incorrectIndent #-} -- | @'indentGuard' spaceConsumer ord ref@ first consumes all white space -- (indentation) with @spaceConsumer@ parser, then it checks the column -- position. Ordering between current indentation level and the reference -- indentation level @ref@ should be @ord@, otherwise the parser fails. On -- success the current column position is returned. -- -- When you want to parse a block of indentation, first run this parser with -- arguments like @'indentGuard' spaceConsumer 'GT' 'pos1'@—this will make -- sure you have some indentation. Use returned value to check indentation -- on every subsequent line according to syntax of your language. indentGuard :: MonadParsec e s m => m () -- ^ How to consume indentation (white space) -> Ordering -- ^ Desired ordering between reference level and actual level -> Pos -- ^ Reference indentation level -> m Pos -- ^ Current column (indentation level) indentGuard sc ord ref = do sc actual <- indentLevel if compare actual ref == ord then return actual else incorrectIndent ord ref actual {-# INLINEABLE indentGuard #-} -- | Parse a non-indented construction. This ensures that there is no -- indentation before actual data. Useful, for example, as a wrapper for -- top-level function definitions. -- -- @since 4.3.0 nonIndented :: MonadParsec e s m => m () -- ^ How to consume indentation (white space) -> m a -- ^ How to parse actual data -> m a nonIndented sc p = indentGuard sc EQ pos1 *> p {-# INLINEABLE nonIndented #-} -- | The data type represents available behaviors for parsing of indented -- tokens. This is used in 'indentBlock', which see. -- -- @since 4.3.0 data IndentOpt m a b = IndentNone a -- ^ Parse no indented tokens, just return the value | IndentMany (Maybe Pos) ([b] -> m a) (m b) -- ^ Parse many indented tokens (possibly zero), use given indentation -- level (if 'Nothing', use level of the first indented token); the -- second argument tells how to get the final result, and the third -- argument describes how to parse an indented token | IndentSome (Maybe Pos) ([b] -> m a) (m b) -- ^ Just like 'IndentMany', but requires at least one indented token to -- be present -- | Parse a “reference” token and a number of other tokens that have -- greater (but the same) level of indentation than that of “reference” -- token. Reference token can influence parsing, see 'IndentOpt' for more -- information. -- -- Tokens /must not/ consume newlines after them. On the other hand, the -- first argument of this function /must/ consume newlines among other white -- space characters. -- -- @since 4.3.0 indentBlock :: (MonadParsec e s m, Token s ~ Char) => m () -- ^ How to consume indentation (white space) -> m (IndentOpt m a b) -- ^ How to parse “reference” token -> m a indentBlock sc r = do sc ref <- indentLevel a <- r case a of IndentNone x -> x <$ sc IndentMany indent f p -> do mlvl <- (optional . try) (C.eol *> indentGuard sc GT ref) done <- isJust <$> optional eof case (mlvl, done) of (Just lvl, False) -> indentedItems ref (fromMaybe lvl indent) sc p >>= f _ -> sc *> f [] IndentSome indent f p -> do pos <- C.eol *> indentGuard sc GT ref let lvl = fromMaybe pos indent x <- if | pos <= ref -> incorrectIndent GT ref pos | pos == lvl -> p | otherwise -> incorrectIndent EQ lvl pos xs <- indentedItems ref lvl sc p f (x:xs) {-# INLINEABLE indentBlock #-} -- | Grab indented items. This is a helper for 'indentBlock', it's not a -- part of the public API. indentedItems :: MonadParsec e s m => Pos -- ^ Reference indentation level -> Pos -- ^ Level of the first indented item ('lookAhead'ed) -> m () -- ^ How to consume indentation (white space) -> m b -- ^ How to parse indented tokens -> m [b] indentedItems ref lvl sc p = go where go = do sc pos <- indentLevel done <- isJust <$> optional eof if done then return [] else if | pos <= ref -> return [] | pos == lvl -> (:) <$> p <*> go | otherwise -> incorrectIndent EQ lvl pos -- | Create a parser that supports line-folding. The first argument is used -- to consume white space between components of line fold, thus it /must/ -- consume newlines in order to work properly. The second argument is a -- callback that receives a custom space-consuming parser as argument. This -- parser should be used after separate components of line fold that can be -- put on different lines. -- -- An example should clarify the usage pattern: -- -- > sc = L.space (void spaceChar) empty empty -- > -- > myFold = L.lineFold sc $ \sc' -> do -- > L.symbol sc' "foo" -- > L.symbol sc' "bar" -- > L.symbol sc "baz" -- for the last symbol we use normal space consumer -- -- @since 5.0.0 lineFold :: MonadParsec e s m => m () -- ^ How to consume indentation (white space) -> (m () -> m a) -- ^ Callback that uses provided space-consumer -> m a lineFold sc action = sc >> indentLevel >>= action . void . indentGuard sc GT {-# INLINEABLE lineFold #-} ---------------------------------------------------------------------------- -- Character and string literals -- | The lexeme parser parses a single literal character without quotes. The -- purpose of this parser is to help with parsing of conventional escape -- sequences. It's your responsibility to take care of character literal -- syntax in your language (by surrounding it with single quotes or -- similar). -- -- The literal character is parsed according to the grammar rules defined in -- the Haskell report. -- -- Note that you can use this parser as a building block to parse various -- string literals: -- -- > stringLiteral = char '"' >> manyTill L.charLiteral (char '"') -- -- __Performance note__: the parser is not particularly efficient at the -- moment. charLiteral :: (MonadParsec e s m, Token s ~ Char) => m Char charLiteral = label "literal character" $ do -- The @~@ is needed to avoid requiring a MonadFail constraint, -- and we do know that r will be non-empty if count' succeeds. r <- lookAhead (count' 1 10 anySingle) case listToMaybe (Char.readLitChar r) of Just (c, r') -> c <$ skipCount (length r - length r') anySingle Nothing -> unexpected (Tokens (head r:|[])) {-# INLINEABLE charLiteral #-} ---------------------------------------------------------------------------- -- Numbers -- | Parse an integer in decimal representation according to the format of -- integer literals described in the Haskell report. -- -- If you need to parse signed integers, see 'signed' combinator. -- -- __Note__: before version 6.0.0 the function returned 'Integer', i.e. it -- wasn't polymorphic in its return type. decimal :: (MonadParsec e s m, Token s ~ Char, Integral a) => m a decimal = decimal_ <?> "integer" {-# INLINEABLE decimal #-} -- | A non-public helper to parse decimal integers. decimal_ :: forall e s m a. (MonadParsec e s m, Token s ~ Char, Integral a) => m a decimal_ = mkNum <$> takeWhile1P (Just "digit") Char.isDigit where mkNum = foldl' step 0 . chunkToTokens (Proxy :: Proxy s) step a c = a * 10 + fromIntegral (Char.digitToInt c) {-# INLINE decimal_ #-} -- | Parse an integer in binary representation. Binary number is expected to -- be a non-empty sequence of zeroes “0” and ones “1”. -- -- You could of course parse some prefix before the actual number: -- -- > binary = char '0' >> char' 'b' >> L.binary -- -- @since 7.0.0 binary :: forall e s m a. (MonadParsec e s m, Token s ~ Char, Integral a) => m a binary = mkNum <$> takeWhile1P Nothing isBinDigit <?> "binary integer" where mkNum = foldl' step 0 . chunkToTokens (Proxy :: Proxy s) step a c = a * 2 + fromIntegral (Char.digitToInt c) isBinDigit x = x == '0' || x == '1' {-# INLINEABLE binary #-} -- | Parse an integer in octal representation. Representation of octal -- number is expected to be according to the Haskell report except for the -- fact that this parser doesn't parse “0o” or “0O” prefix. It is a -- responsibility of the programmer to parse correct prefix before parsing -- the number itself. -- -- For example you can make it conform to the Haskell report like this: -- -- > octal = char '0' >> char' 'o' >> L.octal -- -- __Note__: before version 6.0.0 the function returned 'Integer', i.e. it -- wasn't polymorphic in its return type. octal :: forall e s m a. (MonadParsec e s m, Token s ~ Char, Integral a) => m a octal = mkNum <$> takeWhile1P Nothing Char.isOctDigit <?> "octal integer" where mkNum = foldl' step 0 . chunkToTokens (Proxy :: Proxy s) step a c = a * 8 + fromIntegral (Char.digitToInt c) {-# INLINEABLE octal #-} -- | Parse an integer in hexadecimal representation. Representation of -- hexadecimal number is expected to be according to the Haskell report -- except for the fact that this parser doesn't parse “0x” or “0X” prefix. -- It is a responsibility of the programmer to parse correct prefix before -- parsing the number itself. -- -- For example you can make it conform to the Haskell report like this: -- -- > hexadecimal = char '0' >> char' 'x' >> L.hexadecimal -- -- __Note__: before version 6.0.0 the function returned 'Integer', i.e. it -- wasn't polymorphic in its return type. hexadecimal :: forall e s m a. (MonadParsec e s m, Token s ~ Char, Integral a) => m a hexadecimal = mkNum <$> takeWhile1P Nothing Char.isHexDigit <?> "hexadecimal integer" where mkNum = foldl' step 0 . chunkToTokens (Proxy :: Proxy s) step a c = a * 16 + fromIntegral (Char.digitToInt c) {-# INLINEABLE hexadecimal #-} -- | Parse a floating point value as a 'Scientific' number. 'Scientific' is -- great for parsing of arbitrary precision numbers coming from an untrusted -- source. See documentation in "Data.Scientific" for more information. -- -- The parser can be used to parse integers or floating point values. Use -- functions like 'Data.Scientific.floatingOrInteger' from "Data.Scientific" -- to test and extract integer or real values. -- -- This function does not parse sign, if you need to parse signed numbers, -- see 'signed'. -- -- @since 5.0.0 scientific :: forall e s m. (MonadParsec e s m, Token s ~ Char) => m Scientific scientific = do c' <- decimal_ SP c e' <- option (SP c' 0) (try $ dotDecimal_ (Proxy :: Proxy s) c') e <- option e' (try $ exponent_ e') return (Sci.scientific c e) {-# INLINEABLE scientific #-} data SP = SP !Integer {-# UNPACK #-} !Int -- | Parse a floating point number according to the syntax for floating -- point literals described in the Haskell report. -- -- This function does not parse sign, if you need to parse signed numbers, -- see 'signed'. -- -- __Note__: before version 6.0.0 the function returned 'Double', i.e. it -- wasn't polymorphic in its return type. -- -- __Note__: in versions 6.0.0–6.1.1 this function accepted plain integers. float :: (MonadParsec e s m, Token s ~ Char, RealFloat a) => m a float = do c' <- decimal_ Sci.toRealFloat <$> ((do SP c e' <- dotDecimal_ (Proxy :: Proxy s) c' e <- option e' (try $ exponent_ e') return (Sci.scientific c e)) <|> (Sci.scientific c' <$> exponent_ 0)) {-# INLINEABLE float #-} dotDecimal_ :: (MonadParsec e s m, Token s ~ Char) => Proxy s -> Integer -> m SP dotDecimal_ pxy c' = do void (C.char '.') let mkNum = foldl' step (SP c' 0) . chunkToTokens pxy step (SP a e') c = SP (a * 10 + fromIntegral (Char.digitToInt c)) (e' - 1) mkNum <$> takeWhile1P (Just "digit") Char.isDigit {-# INLINE dotDecimal_ #-} exponent_ :: (MonadParsec e s m, Token s ~ Char) => Int -> m Int exponent_ e' = do void (C.char' 'e') (+ e') <$> signed (return ()) decimal_ {-# INLINE exponent_ #-} -- | @'signed' space p@ parser parses an optional sign character (“+” or -- “-”), then if there is a sign it consumes optional white space (using -- @space@ parser), then it runs parser @p@ which should return a number. -- Sign of the number is changed according to the previously parsed sign -- character. -- -- For example, to parse signed integer you can write: -- -- > lexeme = L.lexeme spaceConsumer -- > integer = lexeme L.decimal -- > signedInteger = L.signed spaceConsumer integer signed :: (MonadParsec e s m, Token s ~ Char, Num a) => m () -- ^ How to consume white space after the sign -> m a -- ^ How to parse the number itself -> m a -- ^ Parser for signed numbers signed spc p = option id (lexeme spc sign) <*> p where sign = (id <$ C.char '+') <|> (negate <$ C.char '-') {-# INLINEABLE signed #-}