Data.Attoparsec.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

data Parser a

The Parser type is a monad.

Instances

Monad Parser

Functor Parser

MonadPlus Parser

Applicative Parser

Alternative Parser

data Result r

The result of a parse.

Constructors

Fail !ByteString [String] String

The parse failed. The ByteString 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 (ByteString -> Result 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 !ByteString r

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

Instances

Functor Result

Show r => Show (Result r)

Running parsers

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

Run a parser and return its result.

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

Run a parser and print its result to standard output.

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

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

Combinators

(<?>)

Arguments

:: Parser a

-> String

the name to use if parsing fails

-> Parser a

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 useful in cases where a parser might consume some input before failing, i.e. the parser needs arbitrary lookahead. The downside to using this combinator is that it can retain input for longer than is desirable.

module Data.Attoparsec.Combinator

Parsing individual characters

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'

char :: Char -> Parser Char

Match a specific character.

anyChar :: Parser Char

Match any character.

char8 :: Char -> Parser Word8

Match a specific character, but return its Word8 value.

notChar :: Char -> Parser Char

Match any character except the given one.

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.

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.

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 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.

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.

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.

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 => 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.

State observation and manipulation functions

endOfInput :: Parser ()

Match only if all input has been consumed.

ensure :: Int -> Parser ()

Succeed only if at least n bytes of input are available.