| Copyright | © 2017–2018 Mark Karpov |
|---|---|
| License | BSD 3 clause |
| Maintainer | Mark Karpov <markkarpov92@gmail.com> |
| Stability | experimental |
| Portability | portable |
| Safe Haskell | Safe |
| Language | Haskell2010 |
Control.Applicative.Permutations
Description
This module is a generalization of the package parsec-permutation
authored by Samuel Hoffstaetter:
https://hackage.haskell.org/package/parsec-permutation
This module also takes inspiration from the algorithm is described in: Parsing Permutation Phrases, by Arthur Baars, Andres Löh and Doaitse Swierstra. Published as a functional pearl at the Haskell Workshop 2001:
https://www.cs.ox.ac.uk/jeremy.gibbons/wg21/meeting56/loeh-paper.pdf
From these two works we derive a flexible and general method for parsing
permutations over an Applicative structure. Quite useful in conjunction
with "Free" constructions of Applicatives, Monads, etc.
Other permutation parsing libraries tend towards using special "almost
applicative" combinators for construction which denies the library user
the ability to lift and unlift permutation parsing into any Applicative
computational context. We redefine these combinators as convenience
operators here alongside the equivalent Applicative instance.
For example, suppose we want to parse a permutation of: an optional
string of a's, the character b and an optional c. Using a standard
parsing library combinator char, this can be described using the
Applicative instance by:
test = runPermutation $
(,,) <$> toPermutationWithDefault "" (some (char 'a'))
<*> toPermutation (char 'b')
<*> toPermutationWithDefault '_' (char 'c')Since: 0.2.0
- data Permutation m a
- runPermutation :: (Alternative m, Monad m) => Permutation m a -> m a
- intercalateEffect :: (Alternative m, Monad m) => m b -> Permutation m a -> m a
- toPermutation :: Alternative m => m a -> Permutation m a
- toPermutationWithDefault :: Alternative m => a -> m a -> Permutation m a
Permutation type
data Permutation m a Source #
An Applicative wrapper-type for constructing permutation parsers.
Instances
| Functor m => Functor (Permutation m) Source # | |
| Alternative m => Applicative (Permutation m) Source # | |
Permutation evaluators
Arguments
| :: (Alternative m, Monad m) | |
| => Permutation m a | Permutation specification |
| -> m a | Resulting base monad capable of handling the permutation |
"Unlifts" a permutation parser into a parser to be evaluated.
Arguments
| :: (Alternative m, Monad m) | |
| => m b | Effect to be intercalated between permutation components |
| -> Permutation m a | Permutation specification |
| -> m a | Resulting base monad capable of handling the permutation |
"Unlifts" a permutation parser into a parser to be evaluated with an intercalated effect. Useful for separators between permutation elements.
For example, suppose that similar to above we want to parse a permutation
of: an optional string of a's, the character b and an optional c.
However, we also want each element of the permutation to be separated
by a colon. Using a standard parsing library combinator char, this can
be described using the Applicative instance by:
test = intercalateEffect (char ':') $
(,,) <$> toPermutationWithDefault "" (some (char 'a'))
<*> toPermutation (char 'b')
<*> toPermutationWithDefault '_' (char 'c')This will accept strings such as: "a:b:c", "b:c:a", "b:aa", "b", etc.
Note that the effect is intercalated between permutation components and that:
- There is never an effect parsed preceeding the first component of the permutation.
- There is never an effect parsed following the last component of the permutation.
- No effects are intercalated between missing components with a default value.
Permutation constructors
Arguments
| :: Alternative m | |
| => m a | Permutation component |
| -> Permutation m a |
"Lifts" a parser to a permutation parser.
toPermutationWithDefault Source #
Arguments
| :: Alternative m | |
| => a | Default Value |
| -> m a | Permutation component |
| -> Permutation m a |
"Lifts" a parser with a default value to a permutation parser.
If no permutation containing the supplied parser can be parsed from the input, then the supplied default value is returned in lieu of a parse result.