Data.Attoparsec.ByteString.Char8

Simple, efficient, character-oriented combinator parsing for ByteString strings, loosely based on the Parsec library.

Character encodings

This module is intended for parsing text that is represented using an 8-bit character set, e.g. ASCII or ISO-8859-15. It does not make any attempt to deal with character encodings, multibyte characters, or wide characters. In particular, all attempts to use characters above code point U+00FF will give wrong answers.

Code points below U+0100 are simply translated to and from their numeric values, so e.g. the code point U+00A4 becomes the byte 0xA4 (which is the Euro symbol in ISO-8859-15, but the generic currency sign in ISO-8859-1). Haskell Char values above U+00FF are truncated, so e.g. U+1D6B7 is truncated to the byte 0xB7.

Parser types

type Parser = Parser ByteString

type Result = IResult ByteString

data IResult t r

The result of a parse. This is parameterised over the type t of string that was processed.

This type is an instance of Functor, where fmap transforms the value in a Done result.

Constructors

Fail t [String] String

The parse failed. The t parameter is the input that had not yet been consumed when the failure occurred. The [String] is a list of contexts in which the error occurred. The String is the message describing the error, if any.

Partial (t -> IResult t r)

Supply this continuation with more input so that the parser can resume. To indicate that no more input is available, use an empty string.

Done t r

The parse succeeded. The t parameter is the input that had not yet been consumed (if any) when the parse succeeded.

Instances

Functor (IResult t)

(Show t, Show r) => Show (IResult t r)

(NFData t, NFData r) => NFData (IResult t r)

compareResults :: (Eq t, Eq r) => IResult t r -> IResult t r -> Maybe Bool

Compare two IResult values for equality.

If both IResults are Partial, the result will be Nothing, as they are incomplete and hence their equality cannot be known. (This is why there is no Eq instance for IResult.)

Running parsers

parse :: Parser a -> ByteString -> Result a

Run a parser.

feed :: Result r -> ByteString -> Result r

If a parser has returned a Partial result, supply it with more input.

parseOnly :: Parser a -> ByteString -> Either String a

Run a parser that cannot be resupplied via a Partial result.

parseTest :: Show a => Parser a -> ByteString -> IO ()

Run a parser and print its result to standard output.

parseWith

Arguments

:: Monad m

=> m ByteString

An action that will be executed to provide the parser with more input, if necessary. The action must return an empty string when there is no more input available.

-> Parser a

-> ByteString

Initial input for the parser.

-> m (Result a)

Run a parser with an initial input string, and a monadic action that can supply more input if needed.

Result conversion

maybeResult :: Result r -> Maybe r

Convert a Result value to a Maybe value. A Partial result is treated as failure.

eitherResult :: Result r -> Either String r

Convert a Result value to an Either value. A Partial result is treated as failure.

Combinators

(<?>)

Arguments

:: Parser a

-> String

the name to use if parsing fails

-> Parser a

Name the parser, in case failure occurs.

try :: Parser a -> Parser a

Attempt a parse, and if it fails, rewind the input so that no input appears to have been consumed.

This combinator is provided for compatibility with Parsec. Attoparsec parsers always backtrack on failure.

module Data.Attoparsec.Combinator

Parsing individual characters

char :: Char -> Parser Char

Match a specific character.

char8 :: Char -> Parser Word8

Match a specific character, but return its Word8 value.

anyChar :: Parser Char

Match any character.

notChar :: Char -> Parser Char

Match any character except the given one.

peekChar :: Parser (Maybe Char)

Match any character. Returns Nothing if end of input has been reached. Does not consume any input.

Note: Because this parser does not fail, do not use it with combinators such as many, because such parsers loop until a failure occurs. Careless use will thus result in an infinite loop.

satisfy :: (Char -> Bool) -> Parser Char

The parser satisfy p succeeds for any byte for which the predicate p returns True. Returns the byte that is actually parsed.

digit = satisfy isDigit
    where isDigit c = c >= '0' && c <= '9'

Special character parsers

digit :: Parser Char

Parse a single digit.

letter_iso8859_15 :: Parser Char

Match a letter, in the ISO-8859-15 encoding.

letter_ascii :: Parser Char

Match a letter, in the ASCII encoding.

space :: Parser Char

Parse a space character.

Note: This parser only gives correct answers for the ASCII encoding. For instance, it does not recognise U+00A0 (non-breaking space) as a space character, even though it is a valid ISO-8859-15 byte.

Fast predicates

isDigit :: Char -> Bool

A fast digit predicate.

isDigit_w8 :: Word8 -> Bool

A fast digit predicate.

isAlpha_iso8859_15 :: Char -> Bool

A fast alphabetic predicate for the ISO-8859-15 encoding

Note: For all character encodings other than ISO-8859-15, and almost all Unicode code points above U+00A3, this predicate gives wrong answers.

isAlpha_ascii :: Char -> Bool

A fast alphabetic predicate for the ASCII encoding

Note: For all character encodings other than ASCII, and almost all Unicode code points above U+007F, this predicate gives wrong answers.

isSpace :: Char -> Bool

Fast predicate for matching ASCII space characters.

Note: This predicate only gives correct answers for the ASCII encoding. For instance, it does not recognise U+00A0 (non-breaking space) as a space character, even though it is a valid ISO-8859-15 byte. For a Unicode-aware and only slightly slower predicate, use isSpace

isSpace_w8 :: Word8 -> Bool

Fast Word8 predicate for matching ASCII space characters.

Character classes

inClass :: String -> Char -> Bool

Match any character in a set.

vowel = inClass "aeiou"

Range notation is supported.

halfAlphabet = inClass "a-nA-N"

To add a literal '-' to a set, place it at the beginning or end of the string.

notInClass :: String -> Char -> Bool

Match any character not in a set.

Efficient string handling

string :: ByteString -> Parser ByteString

string s parses a sequence of bytes that identically match s. Returns the parsed string (i.e. s). This parser consumes no input if it fails (even if a partial match).

Note: The behaviour of this parser is different to that of the similarly-named parser in Parsec, as this one is all-or-nothing. To illustrate the difference, the following parser will fail under Parsec given an input of "for":

string "foo" <|> string "for"

The reason for its failure is that the first branch is a partial match, and will consume the letters 'f' and 'o' before failing. In Attoparsec, the above parser will succeed on that input, because the failed first branch will consume nothing.

stringCI :: ByteString -> Parser ByteString

Satisfy a literal string, ignoring case.

skipSpace :: Parser ()

Skip over white space.

skipWhile :: (Char -> Bool) -> Parser ()

Skip past input for as long as the predicate returns True.

take :: Int -> Parser ByteString

Consume exactly n bytes of input.

scan :: s -> (s -> Char -> Maybe s) -> Parser ByteString

A stateful scanner. The predicate consumes and transforms a state argument, and each transformed state is passed to successive invocations of the predicate on each byte of the input until one returns Nothing or the input ends.

This parser does not fail. It will return an empty string if the predicate returns Nothing on the first byte of input.

Note: Because this parser does not fail, do not use it with combinators such as many, because such parsers loop until a failure occurs. Careless use will thus result in an infinite loop.

takeWhile :: (Char -> Bool) -> Parser ByteString

Consume input as long as the predicate returns True, and return the consumed input.

This parser does not fail. It will return an empty string if the predicate returns False on the first byte of input.

Note: Because this parser does not fail, do not use it with combinators such as many, because such parsers loop until a failure occurs. Careless use will thus result in an infinite loop.

takeWhile1 :: (Char -> Bool) -> Parser ByteString

Consume input as long as the predicate returns True, and return the consumed input.

This parser requires the predicate to succeed on at least one byte of input: it will fail if the predicate never returns True or if there is no input left.

takeTill :: (Char -> Bool) -> Parser ByteString

Consume input as long as the predicate returns False (i.e. until it returns True), and return the consumed input.

This parser does not fail. It will return an empty string if the predicate returns True on the first byte of input.

Note: Because this parser does not fail, do not use it with combinators such as many, because such parsers loop until a failure occurs. Careless use will thus result in an infinite loop.

String combinators

The .*> and <*. combinators are intended for use with the OverloadedStrings language extension. They simplify the common task of matching a statically known string, then immediately parsing something else.

An example makes this easier to understand:

{-# LANGUAGE OverloadedStrings #-}

shoeSize = "Shoe size: " .*> decimal

If we were to try to use *> above instead, the type checker would not be able to tell which IsString instance to use for the text in quotes. We would have to be explicit, using either a type signature or the string parser.

(.*>) :: ByteString -> Parser a -> Parser a

Type-specialized version of *> for ByteString.

(<*.) :: Parser a -> ByteString -> Parser a

Type-specialized version of <* for ByteString.

Consume all remaining input

takeByteString :: Parser ByteString

Consume all remaining input and return it as a single string.

takeLazyByteString :: Parser ByteString

Consume all remaining input and return it as a single string.

Text parsing

endOfLine :: Parser ()

Match either a single newline character '\n', or a carriage return followed by a newline character "\r\n".

isEndOfLine :: Word8 -> Bool

A predicate that matches either a carriage return '\r' or newline '\n' character.

isHorizontalSpace :: Word8 -> Bool

A predicate that matches either a space ' ' or horizontal tab '\t' character.

Numeric parsers

decimal :: Integral a => Parser a

Parse and decode an unsigned decimal number.

hexadecimal :: (Integral a, Bits a) => Parser a

Parse and decode an unsigned hexadecimal number. The hex digits 'a' through 'f' may be upper or lower case.

This parser does not accept a leading "0x" string.

signed :: Num a => Parser a -> Parser a

Parse a number with an optional leading '+' or '-' sign character.

double :: Parser Double

Parse a rational number.

The syntax accepted by this parser is the same as for rational.

Note: This function is almost ten times faster than rational, but is slightly less accurate.

The Double type supports about 16 decimal places of accuracy. For 94.2% of numbers, this function and rational give identical results, but for the remaining 5.8%, this function loses precision around the 15th decimal place. For 0.001% of numbers, this function will lose precision at the 13th or 14th decimal place.

This function does not accept string representations of "NaN" or "Infinity".

data Number

A numeric type that can represent integers accurately, and floating point numbers to the precision of a Double.

Constructors

I !Integer

D !Double

Instances

Eq Number

Fractional Number

Data Number

Num Number

Ord Number

Real Number

RealFrac Number

Show Number

Typeable Number

NFData Number

number :: Parser Number

Parse a number, attempting to preserve both speed and precision.

The syntax accepted by this parser is the same as for rational.

Note: This function is almost ten times faster than rational. On integral inputs, it gives perfectly accurate answers, and on floating point inputs, it is slightly less accurate than rational.

This function does not accept string representations of "NaN" or "Infinity".

rational :: Fractional a => Parser a

Parse a rational number.

This parser accepts an optional leading sign character, followed by at least one decimal digit. The syntax similar to that accepted by the read function, with the exception that a trailing '.' or 'e' not followed by a number is not consumed.

Examples with behaviour identical to read, if you feed an empty continuation to the first result:

rational "3"     == Done 3.0 ""
rational "3.1"   == Done 3.1 ""
rational "3e4"   == Done 30000.0 ""
rational "3.1e4" == Done 31000.0, ""

Examples with behaviour identical to read:

rational ".3"    == Fail "input does not start with a digit"
rational "e3"    == Fail "input does not start with a digit"

Examples of differences from read:

rational "3.foo" == Done 3.0 ".foo"
rational "3e"    == Done 3.0 "e"

This function does not accept string representations of "NaN" or "Infinity".

State observation and manipulation functions

endOfInput :: Parser ()

Match only if all input has been consumed.

atEnd :: Parser Bool

Return an indication of whether the end of input has been reached.