Data.Generics.Fixplate.Attributes

Synthetising attributes, partly motivated by Attribute Grammars.

Documentation

newtype Attrib f a

A newtype wrapper around Attr f a so that we can make Attr f an instance of Functor, Foldable and Traversable. This is necessary since Haskell does not allow partial application of type synonyms.

Constructors

Attrib

Fields

unAttrib :: Attr f a

Instances

Functor f => Functor (Attrib f)

Foldable f => Foldable (Attrib f)

Traversable f => Traversable (Attrib f)

(ShowF f, Show a) => Show (Attrib f a)

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

Map over annotations

 annMap f = unAttrib . fmap f . Attrib

Synthetised attributes

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

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)

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

Generalization of scanr for trees.

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)

Inherited attributes

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

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 a

Generalization of scanl for trees

Traversals

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

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)

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 b

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

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

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 Int

Stacking attributes

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

Merges two layers of annotations into a single one.

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)

Merges three layers of annotations into a single one.

annZipWith3 :: Functor f => (a -> b -> c -> d) -> Mu (Ann (Ann (Ann f a) b) c) -> Attr f d