Portability | non-portable |
---|---|
Stability | experimental |
Maintainer | generics@haskell.org |
Safe Haskell | Safe-Infered |
The generic zipper.
- 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)) -> phi 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, last :: (forall b. phi b -> r b -> Ctx f b r ix -> a) -> f r ix -> Maybe a
- next, 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
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.
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 whereSource
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.
cmapA :: Applicative a => (forall ix. phi ix -> r ix -> a (r' ix)) -> phi 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 ixSource
first, last :: (forall b. phi b -> r b -> Ctx f b r ix -> a) -> f r ix -> Maybe aSource
next, prev :: (forall b. phi b -> r b -> Ctx f b r ix -> a) -> phi b -> Ctx f b r ix -> r b -> Maybe aSource
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 g => Zipper phi (:.: Maybe g) | |
Zipper phi g => Zipper phi (:.: [] g) | |
(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 ixSource
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.
on :: (forall xi. phi xi -> r xi -> a) -> Loc phi r ix -> aSource
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 ixSource
Update the current focus without changing its type.
foldZipper :: (forall xi. phi xi -> xi -> r xi) -> Algebra phi r -> Loc phi I0 ix -> r ixSource
Most general eliminator. Both on
and update
can be defined
in terms of foldZipper
.