parsers-0.12.4: Parsing combinators

Copyright | (c) Edward Kmett 2011-2012 (c) Paolo Martini 2007 (c) Daan Leijen 1999-2001
License | BSD-style
Maintainer | ekmett@gmail.com
Stability | provisional
Portability | non-portable
Safe Haskell | Safe
Language | Haskell2010

Text.Parser.Permutation

Description

This module implements permutation parsers. The algorithm is described in:

Parsing Permutation Phrases, by Arthur Baars, Andres Loh and Doaitse Swierstra. Published as a functional pearl at the Haskell Workshop 2001.

Synopsis

- data Permutation m a
- permute :: Alternative m => Permutation m a -> m a
- (<||>) :: Functor m => Permutation m (a -> b) -> m a -> Permutation m b
- (<$$>) :: Functor m => (a -> b) -> m a -> Permutation m b
- (<|?>) :: Functor m => Permutation m (a -> b) -> (a, m a) -> Permutation m b
- (<$?>) :: Functor m => (a -> b) -> (a, m a) -> Permutation m b

# Documentation

data Permutation m a #

The type `Permutation m a` denotes a permutation parser that, when converted by the `permute` function, parses using the base parsing monad `m` and returns a value of type `a` on success.

Normally, a permutation parser is first build with special operators like (`<||>`) and than transformed into a normal parser using `permute`.

Instances

Functor m => Functor (Permutation m) # |
Methods fmap :: (a -> b) -> Permutation m a -> Permutation m b # (<$) :: a -> Permutation m b -> Permutation m a #

permute :: Alternative m => Permutation m a -> m a #

The parser `permute perm` parses a permutation of parser described by `perm`. For example, suppose we want to parse a permutation of: an optional string of `a`'s, the character `b` and an optional `c`. This can be described by:

     test  = permute (tuple <$?> ("",some (char 'a'))
                            <||> char 'b'
                            <|?> ('_',char 'c'))
           where
             tuple a b c  = (a,b,c)

(<||>) :: Functor m => Permutation m (a -> b) -> m a -> Permutation m b infixl 1 #

The expression `perm <||> p` adds parser `p` to the permutation parser `perm`. The parser `p` is not allowed to accept empty input - use the optional combinator (`<|?>`) instead. Returns a new permutation parser that includes `p`.

(<$$>) :: Functor m => (a -> b) -> m a -> Permutation m b infixl 2 #

The expression `f <$$> p` creates a fresh permutation parser consisting of parser `p`. The final result of the permutation parser is the function `f` applied to the return value of `p`. The parser `p` is not allowed to accept empty input - use the optional combinator (`<$?>`) instead.

If the function `f` takes more than one parameter, the type variable `b` is instantiated to a functional type which combines nicely with the adds parser `p` to the (`<||>`) combinator. This results in stylized code where a permutation parser starts with a combining function `f` followed by the parsers. The function `f` gets its parameters in the order in which the parsers are specified, but actual input can be in any order.

(<|?>) :: Functor m => Permutation m (a -> b) -> (a, m a) -> Permutation m b infixl 1 #

The expression `perm <||> (x,p)` adds parser `p` to the permutation parser `perm`. The parser `p` is optional - if it can not be applied, the default value `x` will be used instead. Returns a new permutation parser that includes the optional parser `p`.

(<$?>) :: Functor m => (a -> b) -> (a, m a) -> Permutation m b infixl 2 #

The expression `f <$?> (x,p)` creates a fresh permutation parser consisting of parser `p`. The final result of the permutation parser is the function `f` applied to the return value of `p`. The parser `p` is optional - if it can not be applied, the default value `x` will be used instead.