Text.Trifecta

One or none.

It is useful for modelling any computation that is allowed to fail.

Examples

Using the Alternative instance of Control.Monad.Except, the following functions:

>>> import Control.Monad.Except

>>> canFail = throwError "it failed" :: Except String Int>>> final = return 42                :: Except String Int

Can be combined by allowing the first function to fail:

>>> runExcept $ canFail *> finalLeft "it failed"

>>> runExcept $ optional canFail *> finalRight 42

between open close p parses open, followed by p and close. Returns the value returned by p.

 braces  = between (symbol "{") (symbol "}")

chainl p op x parses zero or more occurrences of p, separated by op. Returns a value obtained by a left associative application of all functions returned by op to the values returned by p. If there are zero occurrences of p, the value x is returned.

chainl1 p op x parses one or more occurrences of p, separated by op Returns a value obtained by a left associative application of all functions returned by op to the values returned by p. . This parser can for example be used to eliminate left recursion which typically occurs in expression grammars.

 expr   = term   `chainl1` addop
 term   = factor `chainl1` mulop
 factor = parens expr <|> integer

 mulop  = (*) <$ symbol "*"
      <|> div <$ symbol "/"

 addop  = (+) <$ symbol "+"
      <|> (-) <$ symbol "-"

chainr p op x parses zero or more occurrences of p, separated by op Returns a value obtained by a right associative application of all functions returned by op to the values returned by p. If there are no occurrences of p, the value x is returned.

chainr1 p op x parses one or more occurrences of p, separated by op Returns a value obtained by a right associative application of all functions returned by op to the values returned by p.

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

count n p parses n occurrences of p. If n is smaller or equal to zero, the parser equals to return []. Returns a list of n values returned by p.

endBy p sep parses zero or more occurrences of p, separated and ended by sep. Returns a list of values returned by p.

  cStatements  = cStatement `endBy` semi

endBy1 p sep parses one or more occurrences of p, separated and ended by sep. Returns a list of values returned by p.

endByNonEmpty p sep parses one or more occurrences of p, separated and ended by sep. Returns a non-empty list of values returned by p.

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

 simpleComment   = do{ string "<!--"
                     ; manyTill anyChar (try (string "-->"))
                     }

Note the overlapping parsers anyChar and string "-->", and therefore the use of the try combinator.

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

 priority = option 0 (digitToInt <$> digit)

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

 commaSep p  = p `sepBy` (symbol ",")

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

sepByNonEmpty p sep parses one or more occurrences of p, separated by sep. Returns a non-empty list of values returned by p.

sepEndBy p sep parses zero or more occurrences of p, separated and optionally ended by sep, ie. haskell style statements. Returns a list of values returned by p.

 haskellStatements  = haskellStatement `sepEndBy` semi

sepEndBy1 p sep parses one or more occurrences of p, separated and optionally ended by sep. Returns a list of values returned by p.

sepEndByNonEmpty p sep parses one or more occurrences of p, separated and optionally ended by sep. Returns a non-empty list of values returned by p.

skipOptional p tries to apply parser p. It will parse p or nothing. It only fails if p fails after consuming input. It discards the result of p. (Plays the role of parsec's optional, which conflicts with Applicative's optional)

p `surroundedBy` f is p surrounded by f. Shortcut for between f f p. As in between, returns the value returned by p.

Zero or more.

Examples

>>> many (putStr "la")lalalalalalalalala... * goes on forever *

>>> many NothingJust []

>>> take 5 <$> many (Just 1)* hangs forever *

Note that this function can be used with Parsers based on Applicatives. In that case many parser will attempt to parse parser zero or more times until it fails.

One or more.

Examples

>>> some (putStr "la")lalalalalalalalala... * goes on forever *

>>> some Nothingnothing

>>> take 5 <$> some (Just 1)* hangs forever *

Note that this function can be used with Parsers based on Applicatives. In that case some parser will attempt to parse parser one or more times until it fails.

Additional functionality needed to describe parsers independent of input type.

Parses a letter or digit. Returns the parsed character.

Parses a digit. Returns the parsed character.

Parses a hexadecimal digit (a digit or a letter between 'a' and 'f' or 'A' and 'F'). Returns the parsed character.

Parses a letter (an upper case or lower case character). Returns the parsed character.

Parses a lower case character. Returns the parsed character.

Parses a newline character ('\n'). Returns a newline character.

As the dual of oneOf, noneOf cs succeeds if the current character is not in the supplied list of characters cs. Returns the parsed character.

 consonant = noneOf "aeiou"

As the dual of oneOf, noneOf cs succeeds if the current character is not in the supplied list of characters cs. Returns the parsed character.

 consonant = noneOf "aeiou"

Parses an octal digit (a character between '0' and '7'). Returns the parsed character.

oneOf cs succeeds if the current character is in the supplied list of characters cs. Returns the parsed character. See also satisfy.

  vowel  = oneOf "aeiou"

oneOfSet cs succeeds if the current character is in the supplied set of characters cs. Returns the parsed character. See also satisfy.

  vowel  = oneOf "aeiou"

Parses a white space character (any character which satisfies isSpace) Returns the parsed character.

Skips zero or more white space characters. See also skipMany.

Parses a tab character ('\t'). Returns a tab character.

Parses an upper case letter. Returns the parsed character.

Additional functionality needed to parse character streams.

Token parser angles p parses p enclosed in angle brackets ('<' and '>'), returning the value of p.

Token parser braces p parses p enclosed in braces ('{' and '}'), returning the value of p.

Token parser brackets p parses p enclosed in brackets ('[' and ']'), returning the value of p.

This token parser parses a single literal character. Returns the literal character value. This parsers deals correctly with escape sequences. The literal character is parsed according to the grammar rules defined in the Haskell report (which matches most programming languages quite closely).

This parser parses a character literal without the surrounding quotation marks.

This parser does NOT swallow trailing whitespace

Token parser colon parses the character ':' and skips any trailing white space. Returns the string ":".

Token parser comma parses the character ',' and skips any trailing white space. Returns the string ",".

Token parser commaSep p parses zero or more occurrences of p separated by comma. Returns a list of values returned by p.

Token parser commaSep1 p parses one or more occurrences of p separated by comma. Returns a list of values returned by p.

Parses a non-negative whole number in the decimal system. Returns the value of the number.

This parser does NOT swallow trailing whitespace

Token parser dot parses the character '.' and skips any trailing white space. Returns the string ".".

This token parser parses a floating point value. Returns the value of the number. The number is parsed according to the grammar rules defined in the Haskell report.

Parses a non-negative whole number in the hexadecimal system. The number should be prefixed with "x" or "X". Returns the value of the number.

This parser does NOT swallow trailing whitespace

Parse a non-reserved identifier or symbol

This token parser parses an integer (a whole number). This parser is like natural except that it can be prefixed with sign (i.e. '-' or '+'). Returns the value of the number. The number can be specified in decimal, hexadecimal or octal. The number is parsed according to the grammar rules in the Haskell report.

This parser parses an integer (a whole number). This parser is like natural except that it can be prefixed with sign (i.e. '-' or '+'). Returns the value of the number. The number can be specified in decimal, hexadecimal or octal. The number is parsed according to the grammar rules in the Haskell report.

This parser does NOT swallow trailing whitespace.

Also, unlike the integer parser, this parser does not admit spaces between the sign and the number.

This token parser is like naturalOrDouble, but handles leading - or +.

This token parser is like naturalOrScientific, but handles leading - or +.

Lift an identifier style into a monad transformer

Using over from the lens package:

liftIdentifierStyle = over styleChars lift

This token parser parses a natural number (a non-negative whole number). Returns the value of the number. The number can be specified in decimal, hexadecimal or octal. The number is parsed according to the grammar rules in the Haskell report.

This token parser parses either natural or a float. Returns the value of the number. This parsers deals with any overlap in the grammar rules for naturals and floats. The number is parsed according to the grammar rules defined in the Haskell report.

This token parser parses either natural or a scientific. Returns the value of the number. This parsers deals with any overlap in the grammar rules for naturals and floats. The number is parsed according to the grammar rules defined in the Haskell report.

Parses a non-negative whole number in the octal system. The number should be prefixed with "o" or "O". Returns the value of the number.

This parser does NOT swallow trailing whitespace

Token parser parens p parses p enclosed in parenthesis, returning the value of p.

parse a reserved operator or identifier using a given style

parse a reserved operator or identifier using a given style given Text.

This token parser parses a floating point value. Returns the value of the number. The number is parsed according to the grammar rules defined in the Haskell report.

Token parser semiSep p parses zero or more occurrences of p separated by semi. Returns a list of values returned by p.

Token parser semiSep1 p parses one or more occurrences of p separated by semi. Returns a list of values returned by p.

This token parser parses a literal string. Returns the literal string value. This parsers deals correctly with escape sequences and gaps. The literal string is parsed according to the grammar rules defined in the Haskell report (which matches most programming languages quite closely).

This token parser behaves as stringLiteral, but for single-quoted strings.

This is a traversal of both actions in contained in an IdentifierStyle.

styleChars :: Traversal (IdentifierStyle m) (IdentifierStyle n) (m Char) (n Char)

This is a lens that can be used to modify the highlight used for this identifier set.

styleHighlight :: Lens' (IdentifierStyle m) Highlight

This is a traversal that can be used to modify the highlights used for both non-reserved and reserved identifiers in this identifier set.

styleHighlights :: Traversal' (IdentifierStyle m) Highlight

This lens can be used to update the action used to recognize subsequent letters in an identifier.

styleLetter :: Lens' (IdentifierStyle m) (m Char)

This lens can be used to update the name for this style of identifier.

styleName :: Lens' (IdentifierStyle m) String

This is a lens that can be used to modify the reserved identifier set.

styleReserved :: Lens' (IdentifierStyle m) (HashSet String)

This is a lens that can be used to modify the highlight used for reserved identifiers in this identifier set.

styleReservedHighlight :: Lens' (IdentifierStyle m) Highlight

This lens can be used to update the action used to recognize the first letter in an identifier.

styleStart :: Lens' (IdentifierStyle m) (m Char)

Token parser symbol s parses string s and skips trailing white space.

Token parser symbolic s parses char s and skips trailing white space.

Token parser textSymbol t parses text s and skips trailing white space.

Skip zero or more bytes worth of white space. More complex parsers are free to consider comments as white space.

Used to describe an input style for constructors, values, operators, etc.

Additional functionality that is needed to tokenize input while ignoring whitespace.

This is a parser transformer you can use to disable syntax highlighting over a range of text you are parsing.

This is a parser transformer you can use to disable the automatic trailing newline (but not whitespace-in-general) consumption of a Token parser.

This is a parser transformer you can use to disable the automatic trailing space consumption of a Token parser.