Safe Haskell	None
Language	Haskell2010

Data.HList.Label3

Contents

Public constructors for labels
Orphan instances

Description

The HList library

A model of labels as needed for extensible records. As before, all the information about labels is recorded in their type, so the labels of records may be purely phantom. In general, Labels are exclusively type-level entities and have no run-time representation.

Record labels are triplets of type-level naturals, namespace, and description. The namespace part helps avoid confusions between labels from different Haskell modules. The description is an arbitrary nullary type constructor.

For the sake of printing, the description is required to be the instance of Show. One must make sure that the show functions does not examine the value, as descr is purely phantom. Here's an example of the good Label description:

    data MyLabelDescr; instance Show MyLabelDescr where show _ = "descr"

which are automated by makeLabels3 from Data.HList.MakeLabel.

This model even allows the labels in a record to belong to different namespaces. To this end, the model employs the predicate for type equality.

Synopsis

data Lbl (x :: HNat) (ns :: *) (desc :: *)
firstLabel :: ns -> desc -> Label (Lbl HZero ns desc)
nextLabel :: Label (Lbl x ns desc) -> desc' -> Label (Lbl (HSucc x) ns desc')
type family MapLabel (xs :: [k]) :: [*]
type family AddLabel (x :: k) :: * where ...

Documentation

>>> let label3 = Label :: Label (Lbl HZero () ())
>>> let label6 = Label :: Label "6"

data Lbl (x :: HNat) (ns :: *) (desc :: *) Source #

Instances

Instances details

(HEqBy HLeFn n m b, ns ~ ns') => HEqBy HLeFn (Lbl n ns desc :: Type) (Lbl m ns' desc' :: Type) b Source #	Data.HList.Label3 labels can only be compared if they belong to the same namespace.
Instance details Defined in Data.HList.HSort
Label t ~ Label (Lbl ix ns n) => SameLabels (Label t :: Type) (Lbl ix ns n :: Type) Source #
Instance details Defined in Data.HList.Label3
Show desc => ShowLabel (Lbl x ns desc :: Type) Source #	Equality on labels (descriptions are ignored) Use generic instance Show label
Instance details Defined in Data.HList.Label3 Methods showLabel :: Label (Lbl x ns desc) -> String Source #
Show desc => Show (Label (Lbl x ns desc)) Source #
Instance details Defined in Data.HList.Label3 Methods showsPrec :: Int -> Label (Lbl x ns desc) -> ShowS # show :: Label (Lbl x ns desc) -> String # showList :: [Label (Lbl x ns desc)] -> ShowS #
(to ~ LabeledTo x, ToSym (to p q) x) => HExtend (to p q) (Proxy (Lbl n ns desc ': xs)) Source #	if the proxy has Data.HList.Label3.Lbl, then everything has to be wrapped in Label to make the kinds match up.
Instance details Defined in Data.HList.Labelable Associated Types type HExtendR (to p q) (Proxy (Lbl n ns desc ': xs)) Source # Methods (.*.) :: to p q -> Proxy (Lbl n ns desc ': xs) -> HExtendR (to p q) (Proxy (Lbl n ns desc ': xs)) Source #
HExtend (Label (Lbl n ns desc)) (Proxy (x ': xs)) Source #	Mixing two label kinds means we have to include `Label`: `>>>` *`let r = label3 .. label6 .. emptyProxy``>>>` `:t r`*r :: Proxy '[Label (Lbl 'HZero () ()), Label "6"]
Instance details Defined in Data.HList.Label3 Associated Types type HExtendR (Label (Lbl n ns desc)) (Proxy (x ': xs)) Source # Methods (.*.) :: Label (Lbl n ns desc) -> Proxy (x ': xs) -> HExtendR (Label (Lbl n ns desc)) (Proxy (x ': xs)) Source #
HExtend (Label (Lbl n ns desc)) (Proxy (Lbl n' ns' desc' ': xs)) Source #	If possible, Label is left off: `>>>` *`let q = label3 .. label3 .. emptyProxy``>>>` `:t q`*q :: Proxy '[Lbl 'HZero () (), Lbl 'HZero () ()]
Instance details Defined in Data.HList.Label3 Associated Types type HExtendR (Label (Lbl n ns desc)) (Proxy (Lbl n' ns' desc' ': xs)) Source # Methods (.*.) :: Label (Lbl n ns desc) -> Proxy (Lbl n' ns' desc' ': xs) -> HExtendR (Label (Lbl n ns desc)) (Proxy (Lbl n' ns' desc' ': xs)) Source #
type ZipTagged (Lbl ix ns n ': ts :: [Type]) (v ': vs) Source #
Instance details Defined in Data.HList.Label3 type ZipTagged (Lbl ix ns n ': ts :: [Type]) (v ': vs) = Tagged (Lbl ix ns n) v ': ZipTagged ts vs
type HExtendR (to p q) (Proxy (Lbl n ns desc ': xs)) Source #
Instance details Defined in Data.HList.Labelable type HExtendR (to p q) (Proxy (Lbl n ns desc ': xs))
type HExtendR (Label (Lbl n ns desc)) (Proxy (Lbl n' ns' desc' ': xs)) Source #
Instance details Defined in Data.HList.Label3 type HExtendR (Label (Lbl n ns desc)) (Proxy (Lbl n' ns' desc' ': xs)) = Proxy (Lbl n ns desc ': (Lbl n' ns' desc' ': xs))
type HExtendR (Label (Lbl n ns desc)) (Proxy (x ': xs)) Source #
Instance details Defined in Data.HList.Label3 type HExtendR (Label (Lbl n ns desc)) (Proxy (x ': xs)) = Proxy (Label (Lbl n ns desc) ': MapLabel (x ': xs))

Public constructors for labels

firstLabel :: ns -> desc -> Label (Lbl HZero ns desc) Source #

Construct the first label

nextLabel :: Label (Lbl x ns desc) -> desc' -> Label (Lbl (HSucc x) ns desc') Source #

Construct the next label

type family MapLabel (xs :: [k]) :: [*] Source #

similar to Data.HList.Record.Labels1, but avoids producing Label (Label x)

Instances

Instances details

type MapLabel ('[] :: [k]) Source #
Instance details Defined in Data.HList.Label3 type MapLabel ('[] :: [k]) = '[] :: [Type]
type MapLabel (x ': xs :: [k]) Source #
Instance details Defined in Data.HList.Label3 type MapLabel (x ': xs :: [k]) = AddLabel x ': MapLabel xs

type family AddLabel (x :: k) :: * where ... Source #

Equations

AddLabel (Label x) = Label x
AddLabel x = Label x

Orphan instances

HExtend (Label y) (Proxy (x ': xs)) Source #
Instance details Associated Types type HExtendR (Label y) (Proxy (x ': xs)) Source # Methods (.*.) :: Label y -> Proxy (x ': xs) -> HExtendR (Label y) (Proxy (x ': xs)) Source #
HExtend (Label y) (Proxy (x ': xs)) Source #
Instance details Associated Types type HExtendR (Label y) (Proxy (x ': xs)) Source # Methods (.*.) :: Label y -> Proxy (x ': xs) -> HExtendR (Label y) (Proxy (x ': xs)) Source #
HExtend (Label y) (Proxy (x ': xs)) Source #
Instance details Associated Types type HExtendR (Label y) (Proxy (x ': xs)) Source # Methods (.*.) :: Label y -> Proxy (x ': xs) -> HExtendR (Label y) (Proxy (x ': xs)) Source #
HExtend (Label y) (Proxy (x ': xs)) Source #	Mixing two label kinds means we have to include `Label`: `>>>` *`let s = label6 .. label3 .. emptyProxy``>>>` `:t s`*s :: Proxy '[Label "6", Label (Lbl 'HZero () ())]
Instance details Associated Types type HExtendR (Label y) (Proxy (x ': xs)) Source # Methods (.*.) :: Label y -> Proxy (x ': xs) -> HExtendR (Label y) (Proxy (x ': xs)) Source #