zipper-0.1: Generic zipper for systems 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 f => Zipper f where cmap :: (forall b. Ix s b => s b -> r b -> r' b) -> Ctx f s r ix b -> Ctx f s r' ix b fill :: Ix s b => Ctx f s r ix b -> r b -> f s r ix first :: (forall b. Ix s b => r b -> Ctx f s r ix b -> a) -> f s r ix -> Maybe a last :: (forall b. Ix s b => r b -> Ctx f s r ix b -> a) -> f s r ix -> Maybe a next :: (forall b. Ix s b => r b -> Ctx f s r ix b -> a) -> Ix s b => Ctx f s r ix b -> r b -> Maybe a prev :: (forall b. Ix s b => r b -> Ctx f s r ix b -> a) -> Ix s b => Ctx f s r ix b -> r b -> Maybe a enter :: (Ix s ix, Zipper (PF s)) => s ix -> ix -> Loc s I0 ix down :: Loc s I0 ix -> Maybe (Loc s I0 ix) down' :: Loc s I0 ix -> Maybe (Loc s I0 ix) up :: Loc s I0 ix -> Maybe (Loc s I0 ix) right :: Loc s r ix -> Maybe (Loc s r ix) left :: Loc s r ix -> Maybe (Loc s r ix) dfnext :: Loc s I0 ix -> Maybe (Loc s I0 ix) dfprev :: Loc s I0 ix -> Maybe (Loc s I0 ix) leave :: Loc s I0 ix -> ix on :: (forall xi. Ix s xi => s xi -> r xi -> a) -> Loc s r ix -> a update :: (forall xi. Ix s xi => s xi -> xi -> xi) -> Loc s I0 ix -> Loc s I0 ix foldZipper :: (forall xi. Ix s xi => s xi -> xi -> r xi) -> Algebra s r -> Loc s 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 system of datatypes and over the type of the complete value.

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 f => Zipper 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 cmap :: (forall b. Ix s b => s b -> r b -> r' b) -> Ctx f s r ix b -> Ctx f s r' ix b Source fill :: Ix s b => Ctx f s r ix b -> r b -> f s r ix Source first :: (forall b. Ix s b => r b -> Ctx f s r ix b -> a) -> f s r ix -> Maybe a Source last :: (forall b. Ix s b => r b -> Ctx f s r ix b -> a) -> f s r ix -> Maybe a Source next :: (forall b. Ix s b => r b -> Ctx f s r ix b -> a) -> Ix s b => Ctx f s r ix b -> r b -> Maybe a Source prev :: (forall b. Ix s b => r b -> Ctx f s r ix b -> a) -> Ix s b => Ctx f s r ix b -> r b -> Maybe a Source Instances Zipper U Zipper (I xi) Zipper (K a) (Zipper f, Zipper g) => Zipper (f :+: g) (Zipper f, Zipper g) => Zipper (f :*: g) Zipper f => Zipper (f :>: xi) (Constructor c, Zipper f) => Zipper (C c f)

Interface

enter :: (Ix s ix, Zipper (PF s)) => s ix -> ix -> Loc s I0 ix Source

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

leave :: Loc s I0 ix -> ix Source

Return the entire value, independent of the current focus.

on :: (forall xi. Ix s xi => s xi -> r xi -> a) -> Loc s r ix -> a Source

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

update :: (forall xi. Ix s xi => s xi -> xi -> xi) -> Loc s I0 ix -> Loc s I0 ix Source

Update the current focus without changing its type.

foldZipper :: (forall xi. Ix s xi => s xi -> xi -> r xi) -> Algebra s r -> Loc s I0 ix -> r ix Source

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

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