polyparse-1.2: A variety of alternative parser combinator libraries.




The Parse class is a replacement for the standard Read class.

The Parse class is a replacement for the standard Read class. It is a specialisation of the (poly) Parser monad for String input. There are instances defined for all Prelude types. For user-defined types, you can write your own instance, or use DrIFT to generate them automatically, e.g. {-! derive : Parse !-}

type TextParser a = Parser Char aSource

A synonym for Parser Char, i.e. string input (no state)

class Parse a whereSource

The class Parse is a replacement for Read, operating over String input. Essentially, it permits better error messages for why something failed to parse. It is rather important that parse can read back exactly what is generated by the corresponding instance of show. To apply a parser to some text, use runParser.


parse :: TextParser aSource

A straightforward parser for an item. (A minimal definition of a class instance requires either |parse| or |parsePrec|.)

parsePrec :: Int -> TextParser aSource

A straightforward parser for an item, given the precedence of any surrounding expression. (Precedence determines whether parentheses are mandatory or optional.)

parseList :: TextParser [a]Source

Parsing a list of items by default accepts the [] and comma syntax, except when the list is really a character string using "".


Parse Bool 
Parse Char 
Parse Double 
Parse Float 
Parse Int 
Parse Integer 
Parse Ordering 
Parse () 
Parse a => Parse [a] 
Parse a => Parse (Maybe a) 
(Parse a, Parse b) => Parse (Either a b) 
(Parse a, Parse b) => Parse (a, b) 
(Parse a, Parse b, Parse c) => Parse (a, b, c) 

parseByRead :: Read a => String -> TextParser aSource

If there already exists a Read instance for a type, then we can make a Parser for it, but with only poor error-reporting. The string argument is the expected type or value (for error-reporting only).

Combinators specific to string input, lexed haskell-style

word :: TextParser StringSource

One lexical chunk (Haskell-style lexing).

isWord :: String -> TextParser StringSource

Ensure that the next input word is the given string. (Note the input is lexed as haskell, so wordbreaks at spaces, symbols, etc.)

optionalParens :: TextParser a -> TextParser aSource

Allow true string parens around an item.

parens :: Bool -> TextParser a -> TextParser aSource

Allow nested parens around an item (one set required when Bool is True).

field :: Parse a => String -> TextParser aSource

Deal with named field syntax. The string argument is the field name, and the parser returns the value of the field.

constructors :: [(String, TextParser a)] -> TextParser aSource

Parse one of a bunch of alternative constructors. In the list argument, the first element of the pair is the constructor name, and the second is the parser for the rest of the value. The first matching parse is returned.

enumeration :: Show a => String -> [a] -> TextParser aSource

Parse one of the given nullary constructors (an enumeration). The string argument is the name of the type, and the list argument should contain all of the possible enumeration values.

Parsers for literal numerics and characters

parseInt :: Integral a => String -> a -> (Char -> Bool) -> (Char -> Int) -> a -> TextParser aSource

Re-export all the more general combinators from Poly too