Safe Haskell	None

Data.Generics.Traversable

Contents

Open recursion combinators
Closed recursion combinators

Description

All of the functions below work only on «interesting» subterms It is up to the instance writer to decide which subterms are interesting and which subterms should count as immediate. This can also depend on the context c.

The context, denoted c, is a constraint (of kind * -> Constraint) that provides additional facilities to work with the data. Most functions take an implicit parameter ?c :: p c; it's used to disambugate which context you are referring to. p can be Proxy from the tagged package or any other suitable type constructor.

For more information, see:

Scrap your boilerplate with class: http://research.microsoft.com/en-us/um/people/simonpj/papers/hmap/
Generalizing generic fold: http://ro-che.info/articles/2013-03-11-generalizing-gfoldl.html

Synopsis

Open recursion combinators

class GTraversable c a whereSource

Methods

gtraverse :: (Applicative f, [c :: p c]) => (forall d. c d => d -> f d) -> a -> f aSource

Applicative traversal over (a subset of) immediate subterms. This is a generic version of traverse from Data.Traversable.

The supplied function is applied only to the «interesting» subterms

Other subterms are lifted using pure, and the whole structure is folded back using <*>.

gtraverse has a default implementation const pure, which works for types without interesting subterms (in particular, atomic types).

Instances

GTraversable c Ordering
GTraversable c Char
GTraversable c Double
GTraversable c Float
GTraversable c Integer
GTraversable c Int
GTraversable c Bool
GTraversable c ()
GTraversable c (Ratio n)
c0 a0 => GTraversable c0 (Maybe a0)
c a => GTraversable c [a]
(c0 a0, c0 b0) => GTraversable c0 (Either a0 b0)
(c0 a0, c0 b0) => GTraversable c0 (a0, b0)
(c0 a0, c0 b0, c0 c1) => GTraversable c0 (a0, b0, c1)

gmap :: (GTraversable c a, [c :: p c]) => (forall d. c d => d -> d) -> a -> aSource

Generic map over the immediate subterms

gmapM :: (Monad m, GTraversable c a, [c :: p c]) => (forall d. c d => d -> m d) -> a -> m aSource

Generic monadic map over the immediate subterms

gfoldMap :: (Monoid r, GTraversable c a, [c :: p c]) => (forall d. c d => d -> r) -> a -> rSource

Generic monoidal fold over the immediate subterms (cf. foldMap from Data.Foldable)

gfoldr :: (GTraversable c a, [c :: p c]) => (forall d. c d => d -> r -> r) -> r -> a -> rSource

Generic right fold over the immediate subterms

gfoldl' :: (GTraversable c a, [c :: p c]) => (forall d. c d => r -> d -> r) -> r -> a -> rSource

Generic strict left fold over the immediate subterms

Closed recursion combinators

class (GTraversable (Rec c) a, c a) => Rec c a Source

Rec enables "deep traversals".

It is satisfied automatically when its superclass constraints are satisfied — you are not supposed to declare new instances of this class.

Instances

(GTraversable (Rec c) a, c a) => Rec c a

everywhere :: forall a c p. (Rec c a, [c :: p c]) => (forall d. Rec c d => d -> d) -> a -> aSource

Apply a transformation everywhere in bottom-up manner

everywhere' :: forall a c p. (Rec c a, [c :: p c]) => (forall d. Rec c d => d -> d) -> a -> aSource

Apply a transformation everywhere in top-down manner

everywhereM :: forall m a c p. (Monad m, Rec c a, [c :: p c]) => (forall d. Rec c d => d -> m d) -> a -> m aSource

Monadic variation on everywhere

everything :: forall r a c p. (Rec c a, [c :: p c]) => (r -> r -> r) -> (forall d. Rec c d => d -> r) -> a -> rSource

Strict left fold over all elements, top-down