Data.Extensible.Field

Flexible records and variants Example: https://github.com/fumieval/extensible/blob/master/examples/records.hs

Documentation

newtype Field h kv

A Field h (k ':> v) is h v, but is along with the index k.

Field :: (v -> *) -> Assoc k v -> *

Constructors

Field

Fields

getField :: h (AssocValue kv)

Instances

Wrapper k h => Wrapper (Assoc k k) (Field k k h)

(KnownSymbol k1, Wrapper k h, Show (Repr k h v)) => Show (Field k Symbol h ((:>) Symbol k k v))

Shows in field @= value style instead of the derived one.

type Repr (Assoc k1 k) (Field k k1 h) kv = Repr k h (AssocValue k k1 kv)

(@=) :: Wrapper h => FieldName k -> Repr h v -> Field h (k :> v) infix 1

Annotate a value by the field name.

(<@=>) :: (Functor f, Wrapper h) => FieldName k -> f (Repr h v) -> Comp f (Field h) (k :> v) infix 1

Lifted (@=)

type FieldOptic k = forall f p t xs h v. (Extensible f p t, Associate k v xs, Labelling k p, Wrapper h) => Optic' p f (t (Field h) xs) (Repr h v)

FieldOptic s is a type of optics that points a field/constructor named s.

The yielding fields can be Lenses for Records and Prisms for Variants.

FieldOptic "foo" = Associate "foo" a xs => Lens' (Record xs) a
FieldOptic "foo" = Associate "foo" a xs => Prism' (Variant xs) a

FieldOptics can be generated using mkField defined in the Data.Extensible.TH module.

type FieldName k = Optic' (LabelPhantom k) Proxy (Inextensible (Field Proxy) `[k :> ()]`) ()

When you see this type as an argument, it expects a FieldLens. This type is used to resolve the name of the field internally.

Records and variants

type RecordOf h = (:*) (Field h)

The type of records which contain several fields.

RecordOf :: (v -> *) -> [Assoc k v] -> *

type Record = RecordOf Identity

Simple record

emptyRecord :: Record []

An empty Record.

type VariantOf h = (:|) (Field h)

The dual of RecordOf

VariantOf :: (v -> *) -> [Assoc k v] -> *

type Variant = VariantOf Identity

Simple variant

Matching

matchWithField :: (forall x. f x -> g x -> r) -> RecordOf f xs -> VariantOf g xs -> r

matchField :: RecordOf (Match h r) xs -> VariantOf h xs -> r

Constraint

type family AssocKey kv :: k

Equations

AssocKey (k :> v) = k

type family AssocValue kv :: v

Equations

AssocValue (k :> v) = v

class (pk (AssocKey kv), pv (AssocValue kv)) => KeyValue pk pv kv

Instances

(pk k2, pv v) => KeyValue k k pk pv ((:>) k k k v)

Internal

data LabelPhantom s a b

A ghostly type which spells the field name

Instances

Profunctor (LabelPhantom k * * s)

type family Labelling s p :: Constraint

Equations

Labelling s (LabelPhantom t) = s ~ t

Labelling s p = ()

data Inextensible h xs

The trivial inextensible data type

Instances

(Functor f, Profunctor p) => Extensible k f p (Inextensible k)