Safe Haskell | Safe-Infered |
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Synthetising attributes, partly motivated by Attribute Grammars, and partly by recursion schemes.

- newtype Attrib f a = Attrib {}
- annMap :: Functor f => (a -> b) -> Attr f a -> Attr f b
- synthetise :: Functor f => (f a -> a) -> Mu f -> Attr f a
- synthetise' :: Functor f => (a -> f b -> b) -> Attr f a -> Attr f b
- synthetiseList :: (Functor f, Foldable f) => ([a] -> a) -> Mu f -> Attr f a
- synthetiseM :: (Traversable f, Monad m) => (f a -> m a) -> Mu f -> m (Attr f a)
- synthCata :: Functor f => (f a -> a) -> Mu f -> Attr f a
- scanCata :: Functor f => (a -> f b -> b) -> Attr f a -> Attr f b
- synthPara :: Functor f => (f (Mu f, a) -> a) -> Mu f -> Attr f a
- synthPara' :: Functor f => (Mu f -> f a -> a) -> Mu f -> Attr f a
- scanPara :: Functor f => (Attr f a -> f b -> b) -> Attr f a -> Attr f b
- synthZygo_ :: Functor f => (f b -> b) -> (f (b, a) -> a) -> Mu f -> Attr f a
- synthZygo :: Functor f => (f b -> b) -> (f (b, a) -> a) -> Mu f -> Attr f (b, a)
- synthZygoWith :: Functor f => (b -> a -> c) -> (f b -> b) -> (f (b, a) -> a) -> Mu f -> Attr f c
- synthAccumCata :: Functor f => (f acc -> (acc, b)) -> Mu f -> (acc, Attr f b)
- synthAccumPara' :: Functor f => (Mu f -> f acc -> (acc, b)) -> Mu f -> (acc, Attr f b)
- mapAccumCata :: Functor f => (f acc -> b -> (acc, c)) -> Attr f b -> (acc, Attr f c)
- synthCataM :: (Traversable f, Monad m) => (f a -> m a) -> Mu f -> m (Attr f a)
- synthParaM :: (Traversable f, Monad m) => (f (Mu f, a) -> m a) -> Mu f -> m (Attr f a)
- synthParaM' :: (Traversable f, Monad m) => (Mu f -> f a -> m a) -> Mu f -> m (Attr f a)
- inherit :: Functor f => (Mu f -> a -> a) -> a -> Mu f -> Attr f a
- inherit' :: Functor f => (a -> b -> a) -> a -> Attr f b -> Attr f a
- inherit2 :: Functor f => (Mu f -> a -> (b, a)) -> a -> Mu f -> Attr f b
- inheritM :: (Traversable f, Monad m) => (Mu f -> a -> m a) -> a -> Mu f -> m (Attr f a)
- inheritM_ :: (Traversable f, Monad m) => (Mu f -> a -> m a) -> a -> Mu f -> m ()
- topDownSweepM :: (Traversable f, Monad m) => (f () -> a -> m (f a)) -> a -> Mu f -> m ()
- topDownSweepM' :: (Traversable f, Monad m) => (b -> f b -> a -> m (f a)) -> a -> Attr f b -> m ()
- synthAccumL :: Traversable f => (a -> Mu f -> (a, b)) -> a -> Mu f -> (a, Attr f b)
- synthAccumR :: Traversable f => (a -> Mu f -> (a, b)) -> a -> Mu f -> (a, Attr f b)
- synthAccumL_ :: Traversable f => (a -> Mu f -> (a, b)) -> a -> Mu f -> Attr f b
- synthAccumR_ :: Traversable f => (a -> Mu f -> (a, b)) -> a -> Mu f -> Attr f b
- enumerateNodes :: Traversable f => Mu f -> (Int, Attr f Int)
- enumerateNodes_ :: Traversable f => Mu f -> Attr f Int
- synthTransform :: Traversable f => (f a -> a) -> (Attr f a -> Maybe (f (Attr f a))) -> Attr f a -> Attr f a
- synthRewrite :: Traversable f => (f a -> a) -> (Attr f a -> Maybe (f (Attr f a))) -> Attr f a -> Attr f a
- annZip :: Functor f => Mu (Ann (Ann f a) b) -> Attr f (a, b)
- annZipWith :: Functor f => (a -> b -> c) -> Mu (Ann (Ann f a) b) -> Attr f c
- annZip3 :: Functor f => Mu (Ann (Ann (Ann f a) b) c) -> Attr f (a, b, c)
- annZipWith3 :: Functor f => (a -> b -> c -> d) -> Mu (Ann (Ann (Ann f a) b) c) -> Attr f d

# Documentation

A newtype wrapper around `Attr f a`

so that we can make `Attr f`

an instance of Functor, Foldable and Traversable (and Comonad). This is necessary
since Haskell does not allow partial application of type synonyms.

Equivalent to the co-free comonad.

annMap :: Functor f => (a -> b) -> Attr f a -> Attr f bSource

Map over annotations

annMap f = unAttrib . fmap f . Attrib

# Synthetised attributes

synthetise :: Functor f => (f a -> a) -> Mu f -> Attr f aSource

*Synthetised* attributes are created in a bottom-up manner.
As an example, the `sizes`

function computes the sizes of all
subtrees:

sizes :: (Functor f, Foldable f) => Mu f -> Attr f Int sizes = synthetise (\t -> 1 + sum t)

(note that `sum`

here is `Data.Foldable.sum == Prelude.sum . Data.Foldable.toList`

)

See also `synthCata`

.

synthetise' :: Functor f => (a -> f b -> b) -> Attr f a -> Attr f bSource

Generalization of `scanr`

for trees. See also `scanCata`

.

synthetiseList :: (Functor f, Foldable f) => ([a] -> a) -> Mu f -> Attr f aSource

List version of `synthetise`

(compare with Uniplate)

synthetiseM :: (Traversable f, Monad m) => (f a -> m a) -> Mu f -> m (Attr f a)Source

Monadic version of `synthetise`

.

# Synthetised attributes as generalized cata- and paramorphisms

synthCata :: Functor f => (f a -> a) -> Mu f -> Attr f aSource

Synonym for `synthetise`

, motivated by the equation

attribute . synthCata f == cata f

That is, it attributes all subtrees with the result of the corresponding catamorphism.

scanCata :: Functor f => (a -> f b -> b) -> Attr f a -> Attr f bSource

Synonym for `synthetise'`

. Note that this could be a special case of `synthCata`

:

scanCata f == annZipWith (flip const) . synthCata (\(Ann a x) -> f a x)

Catamorphim (`cata`

) is the generalization of `foldr`

from lists to trees;
`synthCata`

is one generalization of `scanr`

, and `scanCata`

is another generalization.

synthPara :: Functor f => (f (Mu f, a) -> a) -> Mu f -> Attr f aSource

Attributes all subtrees with the result of the corresponding paramorphism.

attribute . synthPara f == para f

synthPara' :: Functor f => (Mu f -> f a -> a) -> Mu f -> Attr f aSource

Another version of `synthPara`

.

attribute . synthPara' f == para' f

synthZygo_ :: Functor f => (f b -> b) -> (f (b, a) -> a) -> Mu f -> Attr f aSource

Synthetising zygomorphism.

attribute . synthZygo_ g h == zygo_ g h

synthZygoWith :: Functor f => (b -> a -> c) -> (f b -> b) -> (f (b, a) -> a) -> Mu f -> Attr f cSource

synthAccumCata :: Functor f => (f acc -> (acc, b)) -> Mu f -> (acc, Attr f b)Source

Accumulating catamorphisms. Generalization of `mapAccumR`

from lists to trees.

synthAccumPara' :: Functor f => (Mu f -> f acc -> (acc, b)) -> Mu f -> (acc, Attr f b)Source

Accumulating paramorphisms.

mapAccumCata :: Functor f => (f acc -> b -> (acc, c)) -> Attr f b -> (acc, Attr f c)Source

Could be a special case of `synthAccumCata`

:

mapAccumCata f == second (annZipWith (flip const)) . synthAccumCata (\(Ann b t) -> f b t) where second g (x,y) = (x, g y)

synthCataM :: (Traversable f, Monad m) => (f a -> m a) -> Mu f -> m (Attr f a)Source

Synonym for `synthetiseM`

. If you don't need the result, use `cataM_`

instead.

synthParaM :: (Traversable f, Monad m) => (f (Mu f, a) -> m a) -> Mu f -> m (Attr f a)Source

Monadic version of `synthPara`

. If you don't need the result, use `paraM_`

instead.

synthParaM' :: (Traversable f, Monad m) => (Mu f -> f a -> m a) -> Mu f -> m (Attr f a)Source

Monadic version of `synthPara'`

.

# Inherited attributes

inherit :: Functor f => (Mu f -> a -> a) -> a -> Mu f -> Attr f aSource

*Inherited* attributes are created in a top-down manner.
As an example, the `depths`

function computes the depth
(the distance from the root, incremented by 1) of all subtrees:

depths :: Functor f => Mu f -> Attr f Int depths = inherit (\_ i -> i+1) 0

inherit' :: Functor f => (a -> b -> a) -> a -> Attr f b -> Attr f aSource

Generalization of `scanl`

from lists to trees.

inherit2 :: Functor f => (Mu f -> a -> (b, a)) -> a -> Mu f -> Attr f bSource

Generalization of `inherit`

. TODO: better name?

inheritM :: (Traversable f, Monad m) => (Mu f -> a -> m a) -> a -> Mu f -> m (Attr f a)Source

Monadic version of `inherit`

.

# Top-down folds

topDownSweepM :: (Traversable f, Monad m) => (f () -> a -> m (f a)) -> a -> Mu f -> m ()Source

Monadic top-down "sweep" of a tree. It's kind of a more complicated folding version of `inheritM`

.
This is unsafe in the sense that the user is responsible to retain the shape of the node.
TODO: better name?

topDownSweepM' :: (Traversable f, Monad m) => (b -> f b -> a -> m (f a)) -> a -> Attr f b -> m ()Source

An attributed version of `topDownSweepM`

. Probably more useful.

# Traversals

synthAccumL :: Traversable f => (a -> Mu f -> (a, b)) -> a -> Mu f -> (a, Attr f b)Source

Synthetising attributes via an accumulating map in a left-to-right fashion
(the order is the same as in `foldl`

).

synthAccumR :: Traversable f => (a -> Mu f -> (a, b)) -> a -> Mu f -> (a, Attr f b)Source

Synthetising attributes via an accumulating map in a right-to-left fashion
(the order is the same as in `foldr`

).

synthAccumL_ :: Traversable f => (a -> Mu f -> (a, b)) -> a -> Mu f -> Attr f bSource

synthAccumR_ :: Traversable f => (a -> Mu f -> (a, b)) -> a -> Mu f -> Attr f bSource

enumerateNodes :: Traversable f => Mu f -> (Int, Attr f Int)Source

We use `synthAccumL`

to number the nodes from `0`

to `(n-1)`

in
a left-to-right traversal fashion, where
`n == length (universe tree)`

is the number of substructures,
which is also returned.

enumerateNodes_ :: Traversable f => Mu f -> Attr f IntSource

# Resynthetising transformations

synthTransform :: Traversable f => (f a -> a) -> (Attr f a -> Maybe (f (Attr f a))) -> Attr f a -> Attr f aSource

Bottom-up transformations which automatically resynthetise attributes in case of changes.

synthRewrite :: Traversable f => (f a -> a) -> (Attr f a -> Maybe (f (Attr f a))) -> Attr f a -> Attr f aSource

Bottom-up transformations to normal form (applying transformation exhaustively) which automatically resynthetise attributes in case of changes.

# Stacking attributes

annZip :: Functor f => Mu (Ann (Ann f a) b) -> Attr f (a, b)Source

Merges two layers of annotations into a single one.