Portability | non-portable |
---|---|

Stability | experimental |

Maintainer | generics@haskell.org |

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`

.