The result of a parse.

Compare two IResult values for equality.

If both IResult s 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 .)

Match only if all input has been consumed.

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

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

Note : this type is deprecated, and will be removed in the next major release. Use the Scientific type instead.

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.

Name the parser, in case failure occurs.

choice ps tries to apply the actions in the list ps in order, until one of them succeeds. Returns the value of the succeeding action.

option x p tries to apply action p . If p fails without consuming input, it returns the value x , otherwise the value returned by p .

priority  = option 0 (digitToInt <$> digit)

many' p applies the action p zero or more times. Returns a list of the returned values of p . The value returned by p is forced to WHNF.

 word  = many' letter

many1 p applies the action p one or more times. Returns a list of the returned values of p .

 word  = many1 letter

many1' p applies the action p one or more times. Returns a list of the returned values of p . The value returned by p is forced to WHNF.

 word  = many1' letter

sepBy p sep applies zero or more occurrences of p , separated by sep . Returns a list of the values returned by p .

commaSep p  = p `sepBy` (char ',')

sepBy' p sep applies zero or more occurrences of p , separated by sep . Returns a list of the values returned by p . The value returned by p is forced to WHNF.

commaSep p  = p `sepBy'` (char ',')

sepBy1 p sep applies one or more occurrences of p , separated by sep . Returns a list of the values returned by p .

commaSep p  = p `sepBy1` (char ',')

sepBy1' p sep applies one or more occurrences of p , separated by sep . Returns a list of the values returned by p . The value returned by p is forced to WHNF.

commaSep p  = p `sepBy1'` (char ',')

manyTill p end applies action p zero or more times until action end succeeds, and returns the list of values returned by p . This can be used to scan comments:

 simpleComment   = string "<!--" *> manyTill anyChar (string "-->")

(Note the overlapping parsers anyChar and string "-->" . While this will work, it is not very efficient, as it will cause a lot of backtracking.)

manyTill' p end applies action p zero or more times until action end succeeds, and returns the list of values returned by p . This can be used to scan comments:

 simpleComment   = string "<!--" *> manyTill' anyChar (string "-->")

(Note the overlapping parsers anyChar and string "-->" . While this will work, it is not very efficient, as it will cause a lot of backtracking.)

The value returned by p is forced to WHNF.

Skip zero or more instances of an action.

Skip one or more instances of an action.

Apply the given action repeatedly, returning every result.

Combine two alternatives.

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

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

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

The parser skip p succeeds for any character for which the predicate p returns True .

skipDigit = skip isDigit
    where isDigit c = c >= '0' && c <= '9'

The parser satisfyWith f p transforms a character, and succeeds if the predicate p returns True on the transformed value. The parser returns the transformed character that was parsed.

Consume exactly n characters of input.

string s parses a sequence of characters 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.

Satisfy a literal string, ignoring case.

Note: this function is currently quite inefficient. Unicode case folding can change the length of a string ("ß" becomes "ss"), which makes a simple, efficient implementation tricky. We have (for now) chosen simplicity over efficiency.

Satisfy a literal string, ignoring case for characters in the ASCII range.

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

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 character 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.

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 character 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.

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

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

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 character 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 character 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.

Like scan , but generalized to return the final state of the scanner.

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 character of input: it will fail if the predicate never returns True or if there is no input left.

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.

Match any character not in a set.

Match any character.

Match a specific character.

Match any character except the given one.

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.

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

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

Return both the result of a parse and the portion of the input that was consumed while it was being parsed.

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

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

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.

Parse and decode an unsigned decimal number.

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

Parse a rational number.

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

Note : this parser is not safe for use with inputs from untrusted sources. An input with a suitably large exponent such as "1e1000000000" will cause a huge Integer to be allocated, resulting in what is effectively a denial-of-service attack.

In most cases, it is better to use double or scientific instead.

Parse a Double .

This parser accepts an optional leading sign character, followed by at most one decimal digit. The syntax is similar to that accepted by the read function, with the exception that a trailing '.' is consumed.

Examples

These examples use this helper:

r :: Parser a -> Text -> Result a
r p s = feed (parse p s) mempty

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

r double "3"     == Done "" 3.0
r double "3.1"   == Done "" 3.1
r double "3e4"   == Done "" 30000.0
r double "3.1e4" == Done "" 31000.0
r double "3e"    == Done "e" 3.0

Examples with behaviour identical to read :

r double ".3"    == Fail ".3" _ _
r double "e3"    == Fail "e3" _ _

Example of difference from read :

r double "3.foo" == Done "foo" 3.0

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

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

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

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

Parse a scientific number.

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

Parse a single digit, as recognised by isDigit .

Parse a letter, as recognised by isAlpha .

Parse a space character, as recognised by isSpace .

Skip over white space.

Obsolete . A type-specialized version of *> for Text . Use *> instead.

Obsolete . A type-specialized version of <* for Text . Use *> instead.

Run a parser and return its result.

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

This function does not force a parser to consume all of its input. Instead, any residual input will be discarded. To force a parser to consume all of its input, use something like this:

parseOnly (myParser <* endOfInput)
 

Run a parser and print its result to standard output.

Convert a Result value to a Maybe value.

Convert a Result value to an Either value.