zipper-0.2: Generic zipper for families of recursive datatypes Source code Contents Index

Generics.MultiRec.Zipper Portability non-portable Stability experimental Maintainer generics@haskell.org

Contents Locations Context frames Generic zipper class Interface

Description

The generic zipper.

Synopsis

data Loc data family Ctx f :: * -> (* -> *) -> * -> * class HFunctor phi f => Zipper phi f where cmapA :: Applicative a => (forall ix. phi ix -> r ix -> a (r' ix)) -> Ctx f b r ix -> a (Ctx f b r' ix) fill :: phi b -> Ctx f b r ix -> r b -> f r ix first :: (forall b. phi b -> r b -> Ctx f b r ix -> a) -> f r ix -> Maybe a last :: (forall b. phi b -> r b -> Ctx f b r ix -> a) -> f r ix -> Maybe a next :: (forall b. phi b -> r b -> Ctx f b r ix -> a) -> phi b -> Ctx f b r ix -> r b -> Maybe a prev :: (forall b. phi b -> r b -> Ctx f b r ix -> a) -> phi b -> Ctx f b r ix -> r b -> Maybe a enter :: (Fam phi, Zipper phi (PF phi)) => phi ix -> ix -> Loc phi I0 ix down :: Loc phi I0 ix -> Maybe (Loc phi I0 ix) down' :: Loc phi I0 ix -> Maybe (Loc phi I0 ix) up :: Loc phi I0 ix -> Maybe (Loc phi I0 ix) right :: Loc phi r ix -> Maybe (Loc phi r ix) left :: Loc phi r ix -> Maybe (Loc phi r ix) dfnext :: Loc phi I0 ix -> Maybe (Loc phi I0 ix) dfprev :: Loc phi I0 ix -> Maybe (Loc phi I0 ix) leave :: Loc phi I0 ix -> ix on :: (forall xi. phi xi -> r xi -> a) -> Loc phi r ix -> a update :: (forall xi. phi xi -> xi -> xi) -> Loc phi I0 ix -> Loc phi I0 ix foldZipper :: (forall xi. phi xi -> xi -> r xi) -> Algebra phi r -> Loc phi I0 ix -> r ix

Locations

data Loc Source

Abstract type of locations. A location contains the current focus and its context. A location is parameterized over the family of datatypes and over the type of the complete value. Instances HFunctor phi (Loc phi)

Context frames

data family Ctx f :: * -> (* -> *) -> * -> * Source

Abstract type of context frames. Not required for the high-level navigation functions.

Generic zipper class

class HFunctor phi f => Zipper phi f where Source

It is in general not necessary to use the generic navigation functions directly. The functions listed in the `Interface' section below are more user-friendly. Methods cmapA :: Applicative a => (forall ix. phi ix -> r ix -> a (r' ix)) -> Ctx f b r ix -> a (Ctx f b r' ix) Source fill :: phi b -> Ctx f b r ix -> r b -> f r ix Source first :: (forall b. phi b -> r b -> Ctx f b r ix -> a) -> f r ix -> Maybe a Source last :: (forall b. phi b -> r b -> Ctx f b r ix -> a) -> f r ix -> Maybe a Source next :: (forall b. phi b -> r b -> Ctx f b r ix -> a) -> phi b -> Ctx f b r ix -> r b -> Maybe a Source prev :: (forall b. phi b -> r b -> Ctx f b r ix -> a) -> phi b -> Ctx f b r ix -> r b -> Maybe a Source Instances Zipper phi U Zipper phi (K a) El phi xi => Zipper phi (I xi) (Constructor c, Zipper phi f) => Zipper phi (C c f) Zipper phi f => Zipper phi (f :>: xi) (Zipper phi f, Zipper phi g) => Zipper phi (f :*: g) (Zipper phi f, Zipper phi g) => Zipper phi (f :+: g)

Interface

enter :: (Fam phi, Zipper phi (PF phi)) => phi ix -> ix -> Loc phi I0 ix Source

Start navigating a datastructure. Returns a location that focuses the entire value and has an empty context.

down :: Loc phi I0 ix -> Maybe (Loc phi I0 ix) Source

Move down to the leftmost child. Returns Nothing if the current focus is a leaf.

down' :: Loc phi I0 ix -> Maybe (Loc phi I0 ix) Source

Move down to the rightmost child. Returns Nothing if the current focus is a leaf.

up :: Loc phi I0 ix -> Maybe (Loc phi I0 ix) Source

Move up to the parent. Returns Nothing if the current focus is the root.

right :: Loc phi r ix -> Maybe (Loc phi r ix) Source

Move to the right sibling. Returns Nothing if the current focus is the rightmost sibling.

left :: Loc phi r ix -> Maybe (Loc phi r ix) Source

Move to the left sibling. Returns Nothing if the current focus is the leftmost sibling.

dfnext :: Loc phi I0 ix -> Maybe (Loc phi I0 ix) Source

Move through all positions in depth-first left-to-right order.

dfprev :: Loc phi I0 ix -> Maybe (Loc phi I0 ix) Source

Move through all positions in depth-first right-to-left order.

leave :: Loc phi I0 ix -> ix Source

Return the entire value, independent of the current focus.

on :: (forall xi. phi xi -> r xi -> a) -> Loc phi r ix -> a Source

Operate on the current focus. This function can be used to extract the current point of focus.

update :: (forall xi. phi xi -> xi -> xi) -> Loc phi I0 ix -> Loc phi I0 ix Source

Update the current focus without changing its type.

foldZipper :: (forall xi. phi xi -> xi -> r xi) -> Algebra phi r -> Loc phi I0 ix -> r ix Source

Most general eliminator. Both on and update can be defined in terms of foldZipper.

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