Data.Vinyl.Lens

Documentation

class (i ~ RIndex r rs) => RElem r rs i where

The presence of a field in a record is witnessed by a lens into its value. The third parameter to RElem, i, is there to help the constraint solver realize that this is a decidable predicate with respect to the judgemental equality in k.

Minimal complete definition

rlens

Methods

rlens :: Functor g => sing r -> (f r -> g (f r)) -> Rec f rs -> g (Rec f rs)

We can get a lens for getting and setting the value of a field which is in a record. As a convenience, we take a proxy argument to fix the particular field being viewed. These lenses are compatible with the lens library. Morally:

rlens :: sing r => Lens' (Rec f rs) (f r)

rget :: sing r -> Rec f rs -> f r

For Vinyl users who are not using the lens package, we provide a getter.

rput :: f r -> Rec f rs -> Rec f rs

For Vinyl users who are not using the lens package, we also provide a setter. In general, it will be unambiguous what field is being written to, and so we do not take a proxy argument here.

Instances

RElem k r ((:) k r rs) Z

((~) Nat (RIndex k r ((:) k s rs)) (S i), RElem k r rs i) => RElem k r ((:) k s rs) (S i)

class (is ~ RImage rs ss) => RSubset rs ss is where

If one field set is a subset another, then a lens of from the latter's record to the former's is evident. That is, we can either cast a larger record to a smaller one, or we may replace the values in a slice of a record.

Minimal complete definition

rsubset

Methods

rsubset :: Functor g => (Rec f rs -> g (Rec f rs)) -> Rec f ss -> g (Rec f ss)

This is a lens into a slice of the larger record. Morally, we have:

rsubset :: Lens' (Rec f ss) (Rec f rs)

rcast :: Rec f ss -> Rec f rs

The getter of the rsubset lens is rcast, which takes a larger record to a smaller one by forgetting fields.

rreplace :: Rec f rs -> Rec f ss -> Rec f ss

The setter of the rsubset lens is rreplace, which allows a slice of a record to be replaced with different values.

Instances

RSubset k ([] k) ss ([] Nat)

(RElem k r ss i, RSubset k rs ss is) => RSubset k ((:) k r rs) ss ((:) Nat i is)

type REquivalent rs ss is js = (RSubset rs ss is, RSubset ss rs js)

Two record types are equivalent when they are subtypes of each other.

type (∈) r rs = RElem r rs (RIndex r rs)

A shorthand for RElem which supplies its index.

type (⊆) rs ss = RSubset rs ss (RImage rs ss)

A shorthand for RSubset which supplies its image.

type (≅) rs ss = REquivalent rs ss (RImage rs ss) (RImage ss rs)

A shorthand for REquivalent which supplies its images.

type (<:) rs ss = rs ⊆ ss

A non-unicode equivalent of (⊆).

type (:~:) rs ss = rs ≅ ss

A non-unicode equivalent of (≅).