Data.HList.Variant

The HList library

See CommonMain#Variant for the public (safe) interface.

The implementation here follows Data.Dynamic, though Typeable is not needed.

See broken/VariantP.hs and broken/VariantOld.hs for different approaches to open sums.

Labels for doctests

>>> import Data.HList.RecordPuns
>>> let x = Label :: Label "x"
>>> let y = Label :: Label "y"
>>> let z = Label :: Label "z"
>>> let _left = Label :: Label "left"
>>> let _right = Label :: Label "right"

>>> :set -XQuasiQuotes -XViewPatterns -XDataKinds

• - * Creating Variants

It is necessary to specify the order in which the fields occur, using a data type like

>>> let p = Proxy :: Proxy '[Tagged "left" Char, Tagged "right" Int]

Then this argument can be passed into mkVariant

>>> let v = mkVariant _left 'x' p
>>> let w = mkVariant _right 5  p

>>> :t v
v :: Variant '[Tagged "left" Char, Tagged "right" Int]

>>> :t w
w :: Variant '[Tagged "left" Char, Tagged "right" Int]

>>> [v,w]
[V{left='x'},V{right=5}]

Alternative: a Record as the Proxy

The type of mkVariant also allows using a Record as the proxy. For example:

>>> :{
let p2 = [pun| left right |] where
            left = 'a'
            right = (4::Int)
:}

>>> let v2 = mkVariant _left 'x' p2
>>> let w2 = mkVariant _right 5  p2

>>> :t v2
v2 :: Variant '[Tagged "left" Char, Tagged "right" Int]

>>> :t w2
w2 :: Variant '[Tagged "left" Char, Tagged "right" Int]

>>> (v2,w2)
(V{left='x'},V{right=5})

A polymorphic Proxy

It is also possible to leave the Char and Int as type variables, and have them inferred.

>>> let p3 = Proxy :: Proxy '[Tagged "left" a, Tagged "right" b]

Using p3 takes some care. The following attempt shows the problem:

>>> :{
let v3' = mkVariant _left 'x' p3
    w3' = mkVariant _right (5::Int) p3
:}

>>> :t v3'
v3' :: Variant '[Tagged "left" Char, Tagged "right" b]

>>> :t w3'
w3' :: Variant '[Tagged "left" a, Tagged "right" Int]

Here each use of p3 does not constrain the type of the other use. In some cases those type variables will be inferred from other constraints, such as when putting the variants into a list

>>> [v3', w3']
[V{left='x'},V{right=5}]

In other cases the other tags will be defaulted to (), at least if ExtendedDefaultRules is enabled:

>>> v3'
V{left='x'}

>>> :set -XNoExtendedDefaultRules
>>> v3'
...
...No instance for (Show ...) arising from a use of ‘print’
...

Another way around this issue is to make sure that the proxy is bound in a monomorphic pattern. These are patterns that allow name shadowing.

• p -> ...

• case e of p -> ...

• do p <- e; ...

• implicit parameters let ?p = e in ...
• other patterns involved in mutually recursive bindings

An example of the case:

>>> :{
let (v3,w3) = case p3 of
              p -> (mkVariant _left 'x' p,
                    mkVariant _right (5 :: Int) p)
:}

>>> :t v3
v3 :: Variant '[Tagged "left" Char, Tagged "right" Int]

>>> :t w3
w3 :: Variant '[Tagged "left" Char, Tagged "right" Int]

data Variant (vs :: [*])

Variant vs has an implementation similar to Dynamic, except the contained value is one of the elements of the vs list, rather than being one particular instance of Typeable.

>>> v .!. _right
Nothing

>>> v .!. _left
Just 'x'

In some cases the pun quasiquote works with variants,

>>> let f [pun| left right |] = (left,right)
>>> f v
(Just 'x',Nothing)

>>> f w
(Nothing,Just 5)

>>> let add1 v = hMapV (Fun succ :: Fun '[Enum] '()) v

>>> f (add1 v)
(Just 'y',Nothing)

>>> f (add1 w)
(Nothing,Just 6)

Constructors

Variant !Int Any

Instances

Relabeled Variant

Methods

relabeled :: (HMapTaggedFn (RecordValuesR s) a, HMapTaggedFn (RecordValuesR b) t, SameLengths * (([*] ': s) (([*] ': a) (([*] ': t) (([*] ': b) [[*]])))), ([*] ~ RecordValuesR t) (RecordValuesR b), ([*] ~ RecordValuesR s) (RecordValuesR a), RecordValues b, RecordValues s, Profunctor p, Functor f) => p (Variant a) (f (Variant b)) -> p (Variant s) (f (Variant t))

TypeIndexed Variant TIC

Methods

typeIndexed :: (TypeIndexedCxt s t a b, Profunctor p, Functor f) => p (TIC (TagR a)) (f (TIC (TagR b))) -> p (Variant s) (f (Variant t))

(ExtendsVariant b t, ProjectVariant s a, ProjectExtendVariant s t, HLeftUnion b s bs, HRLabelSet bs, HRearrange (LabelsOf t) bs t) => Projected Variant s t a b

Prism (Variant s) (Variant t) (Variant a) (Variant b)

Methods

projected :: ((LabeledOpticType ~ ty) (LabelableTy Variant), LabeledOpticP ty p, LabeledOpticF ty f) => p (Variant a) (f (Variant b)) -> p (Variant s) (f (Variant t))

HUpdateVariantAtLabelCxt k l e v v' n _e => HUpdateAtLabel k Variant l e v v'

hUpdateAtLabel x e' (mkVariant x e proxy) == mkVariant x e' proxy
hUpdateAtLabel y e' (mkVariant x e proxy) == mkVariant x e  proxy

Methods

hUpdateAtLabel :: Label Variant e -> v -> l v' -> l r'

(HPrism k x s t a b, (~) (* -> * -> *) to ((->) LiftedRep LiftedRep)) => Labelable k x Variant s t a b

make a Prism (Variant s) (Variant t) a b

Associated Types

type LabelableTy (s :: [*] -> *) :: LabeledOpticType

Methods

hLens' :: Label x Variant -> LabeledOptic x Variant s t a b b

(HasField k x (Record vs) a, HFindLabel k x vs n, HNat2Integral n) => HasField k x (Variant vs) (Maybe a)

Methods

hLookupByLabel :: Label x (Variant vs) -> Maybe a -> v

(ApplyAB f te te', HMapCxt Variant f ((:) * l ls) ((:) * l' ls')) => HMapAux Variant f ((:) * te ((:) * l ls)) ((:) * te' ((:) * l' ls'))

Methods

hMapAux :: f -> Variant ((* ': te) ((* ': l) ls)) -> Variant ((* ': te') ((* ': l') ls'))

ApplyAB f te te' => HMapAux Variant f ((:) * te ([] *)) ((:) * te' ([] *))

Methods

hMapAux :: f -> Variant ((* ': te) [*]) -> Variant ((* ': te') [*])

((~) * le (Tagged k l (Maybe e)), HOccursNot * (Label k l) (LabelsOf v)) => HExtend le (Variant v)

Extension for Variants prefers the first value

(l .=. Nothing) .*. v = v
(l .=. Just e)  .*. _ = mkVariant l e Proxy

Associated Types

type HExtendR le (Variant v) :: *

Methods

(.*.) :: le -> Variant v -> HExtendR le (Variant v)

(HasField k l (Variant r) (Maybe u), HasFieldPath True ls u (Maybe v)) => HasFieldPath needJust ((:) * (Label k l) ls) (Variant r) (Maybe v)

Methods

hLookupByLabelPath1 :: Proxy Bool needJust -> Label [*] ((* ': Label k l) ls) -> Variant r -> Maybe v

(Unvariant ((:) * txy ([] *)) txy, (~) * tx (Tagged k t x), (~) * ty (Tagged k t y), (~) * txy (Tagged k t (x, y))) => HUnzip Variant ((:) * tx ([] *)) ((:) * ty ([] *)) ((:) * txy ([] *))

Methods

hUnzip :: Variant ((* ': txy) [*]) -> (Variant ((* ': tx) [*]), Variant ((* ': ty) [*]))

(HUnzip Variant ((:) * x2 xs) ((:) * y2 ys) ((:) * xy2 xys), SameLength * * xs ys, SameLength * * ys xys, (~) * tx (Tagged k t x), (~) * ty (Tagged k t y), (~) * txy (Tagged k t (x, y))) => HUnzip Variant ((:) * tx ((:) * x2 xs)) ((:) * ty ((:) * y2 ys)) ((:) * txy ((:) * xy2 xys))

Methods

hUnzip :: Variant ((* ': txy) ((* ': xy2) xys)) -> (Variant ((* ': tx) ((* ': x2) xs)), Variant ((* ': ty) ((* ': y2) ys)))

(Bounded x, Bounded z, (~) [*] (HRevAppR * ((:) * (Tagged k2 s x) xs) ([] *)) ((:) * (Tagged k1 t z) sx), MkVariant k1 t z ((:) * (Tagged k2 s x) xs)) => Bounded (Variant ((:) * (Tagged k2 s x) xs))

Methods

minBound :: Variant ((* ': Tagged k2 s x) xs)

maxBound :: Variant ((* ': Tagged k2 s x) xs)

Enum x => Enum (Variant ((:) * (Tagged k s x) ([] *)))

While the instances could be written Enum (Variant '[]) Eq/Ord which cannot produce values, so they have instances for empty variants (unsafeEmptyVariant). Enum can produce values, so it is better that fromEnum 0 :: Variant '[] fails with No instance for Enum (Variant '[]) than producing an invalid variant.

Methods

succ :: Variant ((* ': Tagged k s x) [*]) -> Variant ((* ': Tagged k s x) [*])

pred :: Variant ((* ': Tagged k s x) [*]) -> Variant ((* ': Tagged k s x) [*])

toEnum :: Int -> Variant ((* ': Tagged k s x) [*])

fromEnum :: Variant ((* ': Tagged k s x) [*]) -> Int

enumFrom :: Variant ((* ': Tagged k s x) [*]) -> [Variant ((* ': Tagged k s x) [*])]

enumFromThen :: Variant ((* ': Tagged k s x) [*]) -> Variant ((* ': Tagged k s x) [*]) -> [Variant ((* ': Tagged k s x) [*])]

enumFromTo :: Variant ((* ': Tagged k s x) [*]) -> Variant ((* ': Tagged k s x) [*]) -> [Variant ((* ': Tagged k s x) [*])]

enumFromThenTo :: Variant ((* ': Tagged k s x) [*]) -> Variant ((* ': Tagged k s x) [*]) -> Variant ((* ': Tagged k s x) [*]) -> [Variant ((* ': Tagged k s x) [*])]

(Enum x, Bounded x, Enum (Variant ((:) * y z))) => Enum (Variant ((:) * (Tagged k s x) ((:) * y z)))

>>> let t = minBound :: Variant '[Tagged "x" Bool, Tagged "y" Bool]
>>> [t .. maxBound]
[V{x=False},V{x=True},V{y=False},V{y=True}]

Odd behavior

There are some arguments that this instance should not exist.

The last type in the Variant does not need to be Bounded. This means that enumFrom behaves a bit unexpectedly:

>>> [False .. ]
[False,True]

>>> [t .. ]
[V{x=False},V{x=True},V{y=False},V{y=True},V{y=*** Exception: Prelude.Enum.Bool.toEnum: bad argument

This is a "feature" because it allows an Enum (Variant '[Tagged "a" Bool, Tagged "n" Integer])

Another difficult choice is that the lower bound is fromEnum 0 rather than minBound:

>>> take 5 [ minBound :: Variant '[Tagged "b" Bool, Tagged "i" Int] .. ]
[V{b=False},V{b=True},V{i=0},V{i=1},V{i=2}]

Methods

succ :: Variant ((* ': Tagged k s x) ((* ': y) z)) -> Variant ((* ': Tagged k s x) ((* ': y) z))

pred :: Variant ((* ': Tagged k s x) ((* ': y) z)) -> Variant ((* ': Tagged k s x) ((* ': y) z))

toEnum :: Int -> Variant ((* ': Tagged k s x) ((* ': y) z))

fromEnum :: Variant ((* ': Tagged k s x) ((* ': y) z)) -> Int

enumFrom :: Variant ((* ': Tagged k s x) ((* ': y) z)) -> [Variant ((* ': Tagged k s x) ((* ': y) z))]

enumFromThen :: Variant ((* ': Tagged k s x) ((* ': y) z)) -> Variant ((* ': Tagged k s x) ((* ': y) z)) -> [Variant ((* ': Tagged k s x) ((* ': y) z))]

enumFromTo :: Variant ((* ': Tagged k s x) ((* ': y) z)) -> Variant ((* ': Tagged k s x) ((* ': y) z)) -> [Variant ((* ': Tagged k s x) ((* ': y) z))]

enumFromThenTo :: Variant ((* ': Tagged k s x) ((* ': y) z)) -> Variant ((* ': Tagged k s x) ((* ': y) z)) -> Variant ((* ': Tagged k s x) ((* ': y) z)) -> [Variant ((* ': Tagged k s x) ((* ': y) z))]

(Eq (Variant xs), Eq x) => Eq (Variant ((:) * x xs))

Methods

(==) :: Variant ((* ': x) xs) -> Variant ((* ': x) xs) -> Bool

(/=) :: Variant ((* ': x) xs) -> Variant ((* ': x) xs) -> Bool

Eq (Variant ([] *))

Methods

(==) :: Variant [*] -> Variant [*] -> Bool

(/=) :: Variant [*] -> Variant [*] -> Bool

(Typeable * (Variant v), GfoldlVariant v v, GunfoldVariant v v, VariantConstrs v) => Data (Variant v)

Methods

gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> Variant v -> c (Variant v)

gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (Variant v)

toConstr :: Variant v -> Constr

dataTypeOf :: Variant v -> DataType

dataCast1 :: Typeable (* -> *) t => (forall d. Data d => c (t d)) -> Maybe (c (Variant v))

dataCast2 :: Typeable (* -> * -> *) t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (Variant v))

gmapT :: (forall b. Data b => b -> b) -> Variant v -> Variant v

gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Variant v -> r

gmapQr :: (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Variant v -> r

gmapQ :: (forall d. Data d => d -> u) -> Variant v -> [u]

gmapQi :: Int -> (forall d. Data d => d -> u) -> Variant v -> u

gmapM :: Monad m => (forall d. Data d => d -> m d) -> Variant v -> m (Variant v)

gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Variant v -> m (Variant v)

gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Variant v -> m (Variant v)

(Ord x, Ord (Variant xs)) => Ord (Variant ((:) * x xs))

Methods

compare :: Variant ((* ': x) xs) -> Variant ((* ': x) xs) -> Ordering

(<) :: Variant ((* ': x) xs) -> Variant ((* ': x) xs) -> Bool

(<=) :: Variant ((* ': x) xs) -> Variant ((* ': x) xs) -> Bool

(>) :: Variant ((* ': x) xs) -> Variant ((* ': x) xs) -> Bool

(>=) :: Variant ((* ': x) xs) -> Variant ((* ': x) xs) -> Bool

max :: Variant ((* ': x) xs) -> Variant ((* ': x) xs) -> Variant ((* ': x) xs)

min :: Variant ((* ': x) xs) -> Variant ((* ': x) xs) -> Variant ((* ': x) xs)

Ord (Variant ([] *))

Methods

compare :: Variant [*] -> Variant [*] -> Ordering

(<) :: Variant [*] -> Variant [*] -> Bool

(<=) :: Variant [*] -> Variant [*] -> Bool

(>) :: Variant [*] -> Variant [*] -> Bool

(>=) :: Variant [*] -> Variant [*] -> Bool

max :: Variant [*] -> Variant [*] -> Variant [*]

min :: Variant [*] -> Variant [*] -> Variant [*]

ReadVariant v => Read (Variant v)

A corresponding read instance

Methods

readsPrec :: Int -> ReadS (Variant v)

readList :: ReadS [Variant v]

readPrec :: ReadPrec (Variant v)

readListPrec :: ReadPrec [Variant v]

ShowVariant vs => Show (Variant vs)

Variants are not opaque

Methods

showsPrec :: Int -> Variant vs -> ShowS

show :: Variant vs -> String

showList :: [Variant vs] -> ShowS

(Semigroup x, Semigroup (Variant ((:) * a b))) => Semigroup (Variant ((:) * (Tagged k t x) ((:) * a b)))

Methods

(<>) :: Variant ((* ': Tagged k t x) ((* ': a) b)) -> Variant ((* ': Tagged k t x) ((* ': a) b)) -> Variant ((* ': Tagged k t x) ((* ': a) b))

sconcat :: NonEmpty (Variant ((* ': Tagged k t x) ((* ': a) b))) -> Variant ((* ': Tagged k t x) ((* ': a) b))

stimes :: Integral b => b -> Variant ((* ': Tagged k t x) ((* ': a) b)) -> Variant ((* ': Tagged k t x) ((* ': a) b))

(Unvariant ((:) * (Tagged k t x) ([] *)) x, Semigroup x) => Semigroup (Variant ((:) * (Tagged k t x) ([] *)))

Methods

(<>) :: Variant ((* ': Tagged k t x) [*]) -> Variant ((* ': Tagged k t x) [*]) -> Variant ((* ': Tagged k t x) [*])

sconcat :: NonEmpty (Variant ((* ': Tagged k t x) [*])) -> Variant ((* ': Tagged k t x) [*])

stimes :: Integral b => b -> Variant ((* ': Tagged k t x) [*]) -> Variant ((* ': Tagged k t x) [*])

(Monoid x, Monoid (Variant ((:) * a b))) => Monoid (Variant ((:) * (Tagged k t x) ((:) * a b)))

Methods

mempty :: Variant ((* ': Tagged k t x) ((* ': a) b))

mappend :: Variant ((* ': Tagged k t x) ((* ': a) b)) -> Variant ((* ': Tagged k t x) ((* ': a) b)) -> Variant ((* ': Tagged k t x) ((* ': a) b))

mconcat :: [Variant ((* ': Tagged k t x) ((* ': a) b))] -> Variant ((* ': Tagged k t x) ((* ': a) b))

(Unvariant ((:) * (Tagged k t x) ([] *)) x, Monoid x) => Monoid (Variant ((:) * (Tagged k t x) ([] *)))

Methods

mempty :: Variant ((* ': Tagged k t x) [*])

mappend :: Variant ((* ': Tagged k t x) [*]) -> Variant ((* ': Tagged k t x) [*]) -> Variant ((* ': Tagged k t x) [*])

mconcat :: [Variant ((* ': Tagged k t x) [*])] -> Variant ((* ': Tagged k t x) [*])

(SameLength * * s a, ExtendsVariant s a, SameLength * * b t, ExtendsVariant b t) => Rearranged [*] Variant s t a b

Methods

rearranged :: (Profunctor p, Functor f) => p (s b) (f (s b)) -> p (s t) (f (s a))

type LabelableTy Variant

type LabelableTy Variant = LabelablePrism

type HExtendR le (Variant v)

type HExtendR le (Variant v) = Variant ((:) * (UnMaybe le) v)

Unsafe operations

unsafeMkVariant

Arguments

:: Int

n

-> v

-> Variant vs

This is only safe if the n'th element of vs has type Tagged t v

unsafeCastVariant :: Variant v -> Variant v'

Safe when (e ~ e') given that

Tagged t e ~ HLookupByHNatR n v
Tagged t' e' ~ HLookupByHNatR n v'

hUpdateAtLabel is the safe version

castVariant :: (RecordValuesR v ~ RecordValuesR v', SameLength v v') => Variant v -> Variant v'

in ghc>=7.8, coerce is probably a better choice

unsafeUnVariant :: Variant v -> e

private destructor. This is safe only if the value contained actually has type e

unsafeEmptyVariant :: Variant '[]

This function is unsafe because it can lead to a runtime error when used together with the HExtend instance (.*.)

>>> print $ (Label :: Label "x") .=. (Nothing :: Maybe ()) .*. unsafeEmptyVariant
V{*** Exception: invalid variant

use mkVariant1 instead

Public constructor

class HasField x (Variant vs) (Maybe v) => MkVariant x v vs | x vs -> v where

Minimal complete definition

mkVariant

Methods

mkVariant

Arguments

:: Label x

the tag

-> v

value to be stored

-> proxy vs

a helper to fix the ordering and types of the potential values that this variant contains. Typically this will be a Proxy, Record or another Variant

-> Variant vs

Instances

(HFindLabel k x vs n, HNat2Integral n, HasField k x (Variant vs) (Maybe v)) => MkVariant k x v vs

Methods

mkVariant :: Label x v -> vs -> proxy vs -> Variant vs

mkVariant1 :: Label k l -> e -> Variant ((:) * (Tagged k l e) ([] *))

Public destructor

hLookupByLabel (synonym .!.)

(.!.)             :: Variant v -> Label x -> Maybe e
hLookupByLabel    :: Label x -> Variant v -> Maybe e

hPrism and hLens' combine this with mkVariant

splitVariant1 :: Variant (Tagged s x ': xs) -> Either x (Variant xs)

splitVariant1' :: Variant (x ': xs) -> Either x (Variant xs)

x ~ Tagged s t

extendVariant :: Variant l -> Variant (e ': l)

Prism

class (SameLength s t, SameLabels s t) => HPrism x s t a b | x s -> a, x t -> b, x s b -> t, x t a -> s where

Make a Prism (Variant s) (Variant t) a b out of a Label.

See Data.HList.Labelable.hLens' is a more overloaded version.

Few type annotations are necessary because of the restriction that s and t have the same labels in the same order, and to get "t" the "a" in "s" is replaced with "b".

Minimal complete definition

hPrism

Methods

hPrism :: (Choice p, Applicative f) => Label x -> p a (f b) -> p (Variant s) (f (Variant t))

Instances

(MkVariant k x b t, HasField k x (Variant s) (Maybe a), SameLength * * s t, SameLabels [*] [*] s t, H2ProjectByLabels ((:) * (Label k x) ([] *)) s si so, H2ProjectByLabels ((:) * (Label k x) ([] *)) t ti to, (~) [*] so to, HUpdateAtLabel k Variant x b s t, HUpdateAtLabel k Variant x a t s) => HPrism k x s t a b

Methods

hPrism :: (Choice p, Applicative f) => Label x s -> p b (f b) -> p (Variant t) (f (Variant a))

Read

class ShowVariant vs where

helper class for defining the Show instance

Minimal complete definition

showVariant

Methods

showVariant :: Variant vs -> ShowS

Instances

(ShowLabel k l, Show v, (~) * lv (Tagged k l v)) => ShowVariant ((:) * lv ([] *))

Methods

showVariant :: Variant ((* ': lv) [*]) -> ShowS

(ShowLabel k l, Show v, ShowVariant ((:) * w ws)) => ShowVariant ((:) * (Tagged k l v) ((:) * w ws))

Methods

showVariant :: Variant ((* ': Tagged k l v) ((* ': w) ws)) -> ShowS

Show

class ReadVariant vs where

Minimal complete definition

readVariant

Methods

readVariant :: ReadP (Variant vs)

Instances

ReadVariant ([] *)

Methods

readVariant :: ReadP (Variant [*])

(ShowLabel k l, Read v, ReadVariant vs, HOccursNot * (Label k l) (LabelsOf vs)) => ReadVariant ((:) * (Tagged k l v) vs)

Methods

readVariant :: ReadP (Variant ((* ': Tagged k l v) vs))

Data

class VariantConstrs (xs :: [*]) where

Minimal complete definition

variantConstrs

Methods

variantConstrs :: DataType -> proxy xs -> [Constr]

Instances

VariantConstrs ([] *)

Methods

variantConstrs :: DataType -> proxy [*] -> [Constr]

(ShowLabel k l, VariantConstrs xs) => VariantConstrs ((:) * (Tagged k l e) xs)

Methods

variantConstrs :: DataType -> proxy ((* ': Tagged k l e) xs) -> [Constr]

class GunfoldVariant (es :: [*]) v where

implementation of gunfold for Variant

In ghci

:set -ddump-deriv -XDeriveDataTypeable
data X a b c = A a | B b | C c deriving (Data,Typeable)

shows that gunfold is defined something like

gunfold k z c = case constrIndex c of
      1 -> k (z Ghci1.A)
      2 -> k (z Ghci1.B)
      _ -> k (z Ghci1.C)

If we instead had

type X a b c = Variant [Tagged "A" a, Tagged "B" b, Tagged "C" c]

Then we could write:

gunfold1 :: (forall b r. Data b => (b -> r) -> c r)
         -> Variant [Tagged "A" a, Tagged "B" b, Tagged "C" c]
gunfold1 f c = case constrIndex c of
      1 -> f mkA
      2 -> f mkB
      _ -> f mkC
  where mkA a = mkVariant (Label :: Label "A") (a :: a) v
        mkB b = mkVariant (Label :: Label "B") (b :: b) v
        mkC c = mkVariant (Label :: Label "C") (c :: c) v
        v = Proxy :: Proxy [Tagged "A" a, Tagged "B" b, Tagged "C" c]

where f = k.z

Minimal complete definition

gunfoldVariant

Methods

gunfoldVariant

Arguments

:: (forall b. Data b => (b -> Variant v) -> c (Variant v))

f = k . z

-> Proxy es

-> Int

-> c (Variant v)

Instances

(MkVariant k l e v, Data e, GunfoldVariant ((:) * b bs) v) => GunfoldVariant ((:) * (Tagged k l e) ((:) * b bs)) v

Methods

gunfoldVariant :: (forall a. Data a => (a -> Variant v) -> c (Variant v)) -> Proxy [*] ((* ': Tagged k l e) ((* ': b) bs)) -> Int -> c (Variant v)

(MkVariant k l e v, Data e) => GunfoldVariant ((:) * (Tagged k l e) ([] *)) v

Methods

gunfoldVariant :: (forall b. Data b => (b -> Variant v) -> c (Variant v)) -> Proxy [*] ((* ': Tagged k l e) [*]) -> Int -> c (Variant v)

class GfoldlVariant xs xs' where

Minimal complete definition

gfoldlVariant

Methods

gfoldlVariant :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> Variant xs -> c (Variant xs')

the same as gfoldl, except the variant that is returned can have more possible values (needed to actually implement gfoldl).

Instances

((~) * a (Tagged k l v), MkVariant k l v r, Data v, GfoldlVariant ((:) * b c) r) => GfoldlVariant ((:) * a ((:) * b c)) r

Methods

gfoldlVariant :: (forall d e. Data d => c (d -> e) -> d -> c e) -> (forall g. g -> c g) -> Variant ((* ': a) ((* ': b) c)) -> c (Variant r)

(Unvariant ((:) * a ([] *)) v, (~) * a (Tagged k l v), Data v, MkVariant k l v b) => GfoldlVariant ((:) * a ([] *)) b

Methods

gfoldlVariant :: (forall d c. Data d => c (d -> c) -> d -> c c) -> (forall g. g -> c g) -> Variant ((* ': a) [*]) -> c (Variant b)

Map

newtype HMapV f

Apply a function to all possible elements of the variant

Constructors

HMapV f

Instances

((~) * vx (Variant x), (~) * vy (Variant y), HMapAux Variant (HFmap f) x y, SameLength * * x y) => ApplyAB (HMapV f) vx vy

apply a function to all values that could be in the variant.

Methods

applyAB :: HMapV f -> vx -> vy

hMapV :: (SameLength' * * y x, SameLength' * * x y, HMapAux Variant (HFmap f) x y) => f -> Variant x -> Variant y

shortcut for applyAB . HMapV. hMap is more general

hMapOutV :: forall x y z f. (SameLength x y, HMapAux Variant (HFmap f) x y, Unvariant y z, HMapOutV_gety x z ~ y) => f -> Variant x -> z

hMapOutV f = unvariant . hMapV f, except an ambiguous type variable is resolved by HMapOutV_gety

type family HMapOutV_gety (x :: [*]) (z :: *) :: [*]

resolves an ambiguous type in hMapOutV

Instances

type HMapOutV_gety ([] *) z

type HMapOutV_gety ([] *) z = [] *

type HMapOutV_gety ((:) * (Tagged k s x) xs) z

type HMapOutV_gety ((:) * (Tagged k s x) xs) z = (:) * (Tagged k s z) (HMapOutV_gety xs z)

HUpdateAtLabel instance

type HUpdateVariantAtLabelCxt l e v v' n _e = (HFindLabel l v n, HFindLabel l v' n, HUpdateAtHNatR n (Tagged l e) v ~ v', HasField l (Variant v) (Maybe _e), HasField l (Record v') e, MkVariant l e v')

HExtend instance

type family UnMaybe le

Instances

type UnMaybe (Maybe e)

type UnMaybe (Maybe e) = e

type UnMaybe (Tagged k l (Maybe e))

type UnMaybe (Tagged k l (Maybe e)) = Tagged k l e

Conversion to an untagged value

class HAllEqVal (x :: [*]) (b :: Bool) | x -> b

Instances

HAllEqVal ([] *) True

(HEq * a a' b, HAllEqVal ((:) * (Tagged k2 t a') xs) b2, (~) Bool (HAnd b b2) b3) => HAllEqVal ((:) * (Tagged k1 s a) ((:) * (Tagged k2 t a') xs)) b3

HAllEqVal ((:) * x ([] *)) True

class HAllEqVal' (x :: [*])

Instances

HAllEqVal' ([] *)

(HAllEqVal' ((:) * ta xs), (~) * a' a, (~) * ta (Tagged k2 t a), (~) * ta' (Tagged k1 t' a')) => HAllEqVal' ((:) * ta' ((:) * ta xs))

HAllEqVal' ((:) * x ([] *))

class Unvariant' v e | v -> e where

Similar to unvariant, except type variables in v will be made equal to e if possible. That allows the type of Nothing to be inferred as Maybe Char.

>>> unvariant' $ x .=. Nothing .*. mkVariant1 y 'y'
'y'

However, this difference leads to more local error messages (Couldn't match type ‘()’ with ‘Char’), rather than the following with unvariant:

Fail
   '("Variant",
     '[Tagged "left" Char, Tagged "right" ()],
     "must have all values equal to ",
     e))

Minimal complete definition

unvariant'

Methods

unvariant' :: Variant v -> e

Instances

(HAllEqVal' ((:) * (Tagged * () e) v), Unvariant v e) => Unvariant' v e

Methods

unvariant' :: Variant v -> e

class Unvariant v e | v -> e where

Convert a Variant which has all possibilities having the same type into a value of that type. Analogous to either id id.

See also unvariant'

Minimal complete definition

unvariant

Methods

unvariant :: Variant v -> e

Instances

(Unvariant1 Bool b v e, HAllEqVal v b, HAllEqVal ((:) * (Tagged * () e) v) b) => Unvariant v e

Methods

unvariant :: Variant v -> e

class Unvariant1 b v e | b v -> e where

Minimal complete definition

unvariant1

Methods

unvariant1 :: Proxy b -> Variant v -> e

Instances

Fail Symbol "Unvariant applied to empty variant" => Unvariant1 k b ([] *) (Proxy Symbol "Unvariant applied to empty variant")

Methods

unvariant1 :: Proxy b [*] -> Variant (Proxy Symbol "Unvariant applied to empty variant") -> e

(~) * v (Tagged k t1 e) => Unvariant1 Bool True ((:) * v vs) e

Methods

unvariant1 :: Proxy True ((* ': v) vs) -> Variant e -> e

Fail * (UnvariantTypeMismatch ((:) * v vs)) => Unvariant1 Bool False ((:) * v vs) (UnvariantTypeMismatch ((:) * v vs))

Methods

unvariant1 :: Proxy False ((* ': v) vs) -> Variant (UnvariantTypeMismatch ((* ': v) vs)) -> e

data UnvariantTypeMismatch (vs :: [*])

Instances

Fail * (UnvariantTypeMismatch ((:) * v vs)) => Unvariant1 Bool False ((:) * v vs) (UnvariantTypeMismatch ((:) * v vs))

Methods

unvariant1 :: Proxy False ((* ': v) vs) -> Variant (UnvariantTypeMismatch ((* ': v) vs)) -> e

unvarianted :: (Unvariant' s a, Unvariant' t b, SameLabels s t, SameLength s t, Functor f) => (a -> f b) -> Variant s -> f (Variant t)

Lens (Variant s) (Variant t) a b

Analogue of Control.Lens.chosen :: Lens (Either a a) (Either b b) a b

unvarianted' :: (Functor f, SameLength' * * t t, SameLabels [*] [*] t t, HAllEqVal ((:) * (Tagged * () a) t) b, HAllEqVal t b, HAllEqVal' ((:) * (Tagged * () a) t), Unvariant1 Bool b t a) => (a -> f a) -> Variant t -> f (Variant t)

Lens' (Variant s) a

where we might have s ~ '[Tagged t1 a, Tagged t2 a]

Zip

class ZipVariant x y xy | x y -> xy, xy -> x y where

Applies to variants that have the same labels in the same order. A generalization of

zipEither :: Either a b -> Either a b -> Maybe (Either (a,a) (b,b))
zipEither (Left a) (Left a') = Just (Left (a,a'))
zipEither (Right a) (Right a') = Just (Right (a,a'))
zipEither _ _ = Nothing

see HZip for zipping other collections

Minimal complete definition

zipVariant

Methods

zipVariant :: Variant x -> Variant y -> Maybe (Variant xy)

Instances

ZipVariant ([] *) ([] *) ([] *)

Methods

zipVariant :: Variant [*] -> Variant [*] -> Maybe (Variant [*])

((~) * tx (Tagged k t x), (~) * ty (Tagged k t y), (~) * txy (Tagged k t (x, y)), ZipVariant xs ys zs, MkVariant k t (x, y) ((:) * txy zs)) => ZipVariant ((:) * tx xs) ((:) * ty ys) ((:) * txy zs)

Methods

zipVariant :: Variant ((* ': tx) xs) -> Variant ((* ': ty) ys) -> Maybe (Variant ((* ': txy) zs))

with a record

class (SameLength v v', SameLabels v v') => ZipVR fs v v' | fs v -> v' where

Apply a record of functions to a variant of values. The functions are selected based on those having the same label as the value.

Minimal complete definition

zipVR_

Methods

zipVR_ :: Record fs -> Variant v -> Variant v'

zipVR is probably a better choice in most situations, since it requires that fs has one function for every element of v

Instances

ZipVR fs ([] *) ([] *)

Methods

zipVR_ :: Record fs -> Variant [*] -> Variant [*]

((~) * lv (Tagged k l v), (~) * lv' (Tagged k l v'), HMemberM * (Label k l) (LabelsOf fs) b, HasFieldM k l (Record fs) f, (~) * (DemoteMaybe (v -> v) f) (v -> v'), MkVariant k l v' ((:) * lv' rs), ZipVR fs vs rs) => ZipVR fs ((:) * lv vs) ((:) * lv' rs)

Methods

zipVR_ :: Record fs -> Variant ((* ': lv) vs) -> Variant ((* ': lv') rs)

zipVR :: (SameLabels fs v, SameLength fs v, ZipVR fs v v', ZipVRCxt fs v v') => Record fs -> Variant v -> Variant v'

>>> let xy = x .*. y .*. emptyProxy
>>> let p = Proxy `asLabelsOf` xy
>>> let vs = [ mkVariant x 1.0 p, mkVariant y () p ]

>>> zipVR (hBuild (+1) id) `map` vs
[V{x=2.0},V{y=()}]

type family ZipVRCxt (fs :: [*]) (xs :: [*]) (ys :: [*]) :: Constraint

Lets zipVR act as if ZipVR fs v v' had an FD v v' -> fs

ZipVRCxt [Tagged s f,  Tagged t g]
         [Tagged s fx, Tagged t gx]
         [Tagged s fy, Tagged t gy]
  = (f ~ (fx -> fy), g ~ (gx -> gy))

Instances

type ZipVRCxt ([] *) ([] *) ([] *)

type ZipVRCxt ([] *) ([] *) ([] *) = ()

type ZipVRCxt ((:) * (Tagged k s f) fs) ((:) * (Tagged k s x) xs) ((:) * (Tagged k s y) ys)

type ZipVRCxt ((:) * (Tagged k s f) fs) ((:) * (Tagged k s x) xs) ((:) * (Tagged k s y) ys) = ((~) * f (x -> y), ZipVRCxt fs xs ys)

Eq

Alternative Eq

eqVariant :: (ZipVariant x2 y x1, HAllEqVal ((:) * (Tagged * () Bool) (HMapOutV_gety x1 Bool)) b, HAllEqVal (HMapOutV_gety x1 Bool) b, Unvariant1 Bool b (HMapOutV_gety x1 Bool) Bool, HMapAux Variant (HFmap UncurryEq) x1 (HMapOutV_gety x1 Bool), SameLength' * * (HMapOutV_gety x1 Bool) x1, SameLength' * * x1 (HMapOutV_gety x1 Bool)) => Variant x2 -> Variant y -> Bool

implemented like and (zipWith (==) xs ys). Behaves the same as the Eq instances for Variant

data UncurryEq

Constructors

UncurryEq

Instances

((~) * ee (e, e), Eq e, (~) * bool Bool) => ApplyAB UncurryEq ee bool

Methods

applyAB :: UncurryEq -> ee -> bool

Ord

Bounded

Enum

Ix (TODO)

Semigroup

Monoid

Projection

class ProjectVariant x y where

convert a variant with more fields into one with fewer (or the same) fields.

>>> let ty = Proxy :: Proxy [Tagged "left" Int, Tagged "right" Int]
>>> let l = mkVariant _left 1 ty
>>> let r = mkVariant _right 2 ty

>>> map projectVariant [l, r] :: [Maybe (Variant '[Tagged "left" Int])]
[Just V{left=1},Nothing]

rearrangeVariant = fromJust . projectVariant is one implementation of rearrangeVariant, since the result can have the same fields with a different order:

>>> let yt = Proxy :: Proxy [Tagged "right" Int, Tagged "left" Int]

>>> map projectVariant [l, r] `asTypeOf` [Just (mkVariant _left 0 yt)]
[Just V{left=1},Just V{right=2}]

Minimal complete definition

projectVariant

Methods

projectVariant :: Variant x -> Maybe (Variant y)

Instances

ProjectVariant x ([] *)

Methods

projectVariant :: Variant x -> Maybe (Variant [*])

(ProjectVariant x ys, HasField k t (Variant x) (Maybe y), HOccursNot * (Label k t) (LabelsOf ys), (~) * ty (Tagged k t y)) => ProjectVariant x ((:) * ty ys)

Methods

projectVariant :: Variant x -> Maybe (Variant ((* ': ty) ys))

class HAllTaggedLV y => ProjectExtendVariant x y where

projectExtendVariant = fmap extendVariant . projectVariant

where intermediate variant is as large as possible. Used to implement Data.HList.Labelable.projected

Note that:

>>> let r = projectExtendVariant (mkVariant1 Label 1 :: Variant '[Tagged "x" Int])
>>> r :: Maybe (Variant '[Tagged "x" Integer])
Nothing

Minimal complete definition

projectExtendVariant

Methods

projectExtendVariant :: Variant x -> Maybe (Variant y)

Instances

HAllTaggedLV y => ProjectExtendVariant ([] *) y

Methods

projectExtendVariant :: Variant [*] -> Maybe (Variant y)

((~) * lv (Tagged k l v), HMemberM * lv y inY, ProjectExtendVariant' inY lv y, ProjectExtendVariant xs y) => ProjectExtendVariant ((:) * lv xs) y

Methods

projectExtendVariant :: Variant ((* ': lv) xs) -> Maybe (Variant y)

class ProjectExtendVariant' (inY :: Maybe [*]) lv (y :: [*]) where

Minimal complete definition

projectExtendVariant'

Methods

projectExtendVariant' :: Proxy inY -> lv -> Maybe (Variant y)

Instances

ProjectExtendVariant' (Nothing [*]) lv y

Methods

projectExtendVariant' :: Proxy (Maybe [*]) (Nothing [*]) -> lv -> Maybe (Variant y)

(MkVariant k l v y, (~) * lv (Tagged k l v)) => ProjectExtendVariant' (Just [*] t) lv y

Methods

projectExtendVariant' :: Proxy (Maybe [*]) (Just [*] t) -> lv -> Maybe (Variant y)

class (ProjectVariant x yin, ProjectVariant x yout) => SplitVariant x yin yout where

Minimal complete definition

splitVariant

Methods

splitVariant :: Variant x -> Either (Variant yin) (Variant yout)

Instances

(ProjectVariant x yin, ProjectVariant x yout, H2ProjectByLabels (LabelsOf yin) x xi xo, HRearrange (LabelsOf yin) xi yin, HRearrange (LabelsOf yout) xo yout, HLeftUnion xi xo xixo, HRearrange (LabelsOf x) xixo x, HAllTaggedLV x, HAllTaggedLV yin, HAllTaggedLV yout) => SplitVariant x yin yout

Methods

splitVariant :: Variant x -> Either (Variant yin) (Variant yout)

class (HAllTaggedLV y, HAllTaggedLV x) => ExtendsVariant x y where

projectVariant . extendsVariant = Just (when the types match up)

extendVariant is a special case

Minimal complete definition

extendsVariant

Methods

extendsVariant :: Variant x -> Variant y

Instances

(MkVariant k l e y, (~) * le (Tagged k l e), ExtendsVariant ((:) * b bs) y) => ExtendsVariant ((:) * le ((:) * b bs)) y

Methods

extendsVariant :: Variant ((* ': le) ((* ': b) bs)) -> Variant y

(HAllTaggedLV x, Unvariant ((:) * le ([] *)) e, MkVariant k l e x, (~) * le (Tagged k l e)) => ExtendsVariant ((:) * le ([] *)) x

Methods

extendsVariant :: Variant ((* ': le) [*]) -> Variant x

rearrangeVariant :: (SameLength v v', ExtendsVariant v v') => Variant v -> Variant v'

rearrangeVariant is a specialization of extendsVariant whose result is always . see also rearranged

hMaybied :: (Applicative f, Choice p, SameLength' * * x r, SameLength' * * r x, HMapAux HList (HFmap HCastF) x r, VariantToHMaybied v1 x, VariantToHMaybied v2 r, HFoldr HMaybiedToVariantFs [Variant ([] *)] x [Variant v1]) => p (Variant v1) (f (Variant v2)) -> p (Record x) (f (Record r))

Prism (Record tma) (Record tmb) (Variant ta) (Variant tb)

see hMaybied'

data HCastF

Constructors

HCastF

Instances

((~) * mx (Maybe x), (~) * my (Maybe y), HCast y x) => ApplyAB HCastF mx my

Methods

applyAB :: HCastF -> mx -> my

hMaybied' :: (HFoldr HMaybiedToVariantFs [Variant ([] *)] x [Variant v], VariantToHMaybied v x, HMapAux HList (HFmap HCastF) x x, SameLength' * * x x, Choice p, Applicative f) => p (Variant v) (f (Variant v)) -> p (Record x) (f (Record x))

Prism' (Record tma) (Variant ta)

where tma and tmb are lists like

tma ~ '[Tagged x (Maybe a), Tagged y (Maybe b)]
ta  ~ '[Tagged x        a , Tagged y        b ]

If one element of the record is Just, the Variant will contain that element. Otherwise, the prism fails.

Note

The types work out to define a prism:

l = prism' variantToHMaybied (listToMaybe . hMaybiedToVariants)

but the law: s^?l ≡ Just a ==> l # a ≡ s is not followed, because we could have:

  s, s2 :: Record '[Tagged "x" (Maybe Int), Tagged "y" (Maybe Char)]
  s = hBuild (Just 1) (Just '2')
  s2 = hBuild (Just 1) Nothing

  v :: Variant '[Tagged "x" Int, Tagged "y" Char]
  v = mkVariant (Label :: Label "x") 1 Proxy

So that s^?l == Just v. But l#v == s2 /= s, while the law requires l#v == s. hMaybied avoids this problem by only producing a value when there is only one present.

class VariantToHMaybied v r | v -> r, r -> v where

Minimal complete definition

variantToHMaybied

Methods

variantToHMaybied :: Variant v -> Record r

Instances

VariantToHMaybied ([] *) ([] *)

Methods

variantToHMaybied :: Variant [*] -> Record [*]

(VariantToHMaybied v r, HReplicateF nr ConstTaggedNothing () r, (~) * tx (Tagged k t x), (~) * tmx (Tagged k t (Maybe x))) => VariantToHMaybied ((:) * tx v) ((:) * tmx r)

Methods

variantToHMaybied :: Variant ((* ': tx) v) -> Record ((* ': tmx) r)

data ConstTaggedNothing

Constructors

ConstTaggedNothing

Instances

(~) * y (Tagged k t (Maybe e)) => ApplyAB ConstTaggedNothing x y

Methods

applyAB :: ConstTaggedNothing -> x -> y

hMaybiedToVariants :: (HFoldr HMaybiedToVariantFs [Variant '[]] r [Variant v], VariantToHMaybied v r) => Record r -> [Variant v]

Every element of the record that is Just becomes one element in the resulting list. See hMaybied' example types that r and v can take.

data HMaybiedToVariantFs

Constructors

HMaybiedToVariantFs

Instances

((~) * x (Tagged k t (Maybe e), [Variant v]), (~) * y [Variant ((:) * (Tagged k t e) v)], MkVariant k t e ((:) * (Tagged k t e) v)) => ApplyAB HMaybiedToVariantFs x y

Methods

applyAB :: HMaybiedToVariantFs -> x -> y