Portability	unknown
Stability	experimental
Maintainer	bos@serpentine.com
Safe Haskell	None

Data.Attoparsec.ByteString.Char8

Contents

Character encodings
Parser types
Running parsers
- Result conversion
Combinators
Parsing individual characters
Efficient string handling
- String combinators
- Consume all remaining input
Text parsing
Numeric parsers
State observation and manipulation functions

Description

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

Synopsis

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 Source

type Result = IResult ByteString Source

data IResult t r Source

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 Source

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 aSource

Run a parser.

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

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

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

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

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

Run a parser and print its result to standard output.

parseWith Source

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 rSource

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

eitherResult :: Result r -> Either String rSource

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

Combinators

(<?>)Source

Arguments

:: Parser a
-> String	the name to use if parsing fails
-> Parser a

Name the parser, in case failure occurs.

try :: Parser a -> Parser aSource

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 Source

Match a specific character.

char8 :: Char -> Parser Word8 Source

Match a specific character, but return its Word8 value.

anyChar :: Parser Char Source

Match any character.

notChar :: Char -> Parser Char Source

Match any character except the given one.

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

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'

Lookahead

peekChar :: Parser (Maybe Char)Source

Match any character, to perform lookahead. 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.

peekChar' :: Parser Char Source

Match any character, to perform lookahead. Does not consume any input, but will fail if end of input has been reached.

Special character parsers

digit :: Parser Char Source

Parse a single digit.

letter_iso8859_15 :: Parser Char Source

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

letter_ascii :: Parser Char Source

Match a letter, in the ASCII encoding.

space :: Parser Char Source

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 Source

A fast digit predicate.

isDigit_w8 :: Word8 -> Bool Source

A fast digit predicate.

isAlpha_iso8859_15 :: Char -> Bool Source

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 Source

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 Source

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 Source

Fast Word8 predicate for matching ASCII space characters.

Character classes

inClass :: String -> Char -> Bool Source

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 Source

Match any character not in a set.

Efficient string handling

string :: ByteString -> Parser ByteString Source

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 Source

Satisfy a literal string, ignoring case.

skipSpace :: Parser ()Source

Skip over white space.

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

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

take :: Int -> Parser ByteString Source

Consume exactly n bytes of input.

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

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 Source

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 Source

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 Source

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 aSource

Type-specialized version of *> for ByteString.

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

Type-specialized version of <* for ByteString.

Consume all remaining input

takeByteString :: Parser ByteString Source

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

takeLazyByteString :: Parser ByteString Source

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

Text parsing

endOfLine :: Parser ()Source

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

isEndOfLine :: Word8 -> Bool Source

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

isHorizontalSpace :: Word8 -> Bool Source

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

Numeric parsers

decimal :: Integral a => Parser aSource

Parse and decode an unsigned decimal number.

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

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 aSource

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

double :: Parser Double Source

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 Source

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 Source

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 "

rational :: Fractional a => Parser aSource

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 ()Source

Match only if all input has been consumed.

atEnd :: Parser Bool Source

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