Data.Tagged

tagged-0.8.9: Haskell 98 phantom types to avoid unsafely passing dummy arguments

Copyright | 2009-2015 Edward Kmett
License | BSD3
Maintainer | Edward Kmett <ekmett@gmail.com>
Stability | experimental
Portability | portable
Safe Haskell | Safe
Language | Haskell98

Data.Tagged

Contents

- Tagged values
- Conversion
- Proxy methods GHC dropped

Description

Synopsis

- newtype Tagged (s :: k) b = Tagged {
  - unTagged :: b
  }
- retag :: forall {k1} {k2} (s :: k1) b (t :: k2). Tagged s b -> Tagged t b
- untag :: forall {k} (s :: k) b. Tagged s b -> b
- tagSelf :: a -> Tagged a a
- untagSelf :: Tagged a a -> a
- asTaggedTypeOf :: forall {k} s tagged (b :: k). s -> tagged s b -> s
- witness :: Tagged a b -> a -> b
- proxy :: forall {k} (s :: k) a proxy. Tagged s a -> proxy s -> a
- unproxy :: forall {k} (s :: k) a. (Proxy s -> a) -> Tagged s a
- tagWith :: forall {k} proxy (s :: k) a. proxy s -> a -> Tagged s a
- reproxy :: forall {k1} {k2} proxy (a :: k1) (b :: k2). proxy a -> Proxy b

# Tagged values

newtype Tagged (s :: k) b #

A ``Tagged` s b` value is a value `b` with an attached phantom type `s`. This can be used in place of the more traditional but less safe idiom of passing in an undefined value with the type, because unlike an `(s -> b)`, a ``Tagged` s b` can't try to use the argument `s` as a real value.

Moreover, you don't have to rely on the compiler to inline away the extra argument, because the newtype is "free"

`Tagged` has kind `k -> * -> *` if the compiler supports `PolyKinds`, therefore there is an extra `k` showing in the instance haddocks that may cause confusion.

Constructors

Tagged |
Fields unTagged :: b

#### Instances

Instances details

Generic1 (Tagged s :: Type -> Type) # |
Instance details Defined in Data.Tagged Associated Types
type Rep1 (Tagged s :: Type -> Type) |
Instance details Defined in Data.Tagged type Rep1 (Tagged s :: Type -> Type) = D1 ('MetaData "Tagged" "Data.Tagged" "tagged-0.8.9-DfMvf7f6neV1YEOofSyVFB" 'True) (C1 ('MetaCons "Tagged" 'PrefixI 'True) (S1 ('MetaSel ('Just "unTagged") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) Par1))
Methods from1 :: Tagged s a -> Rep1 (Tagged s) a # to1 :: Rep1 (Tagged s) a -> Tagged s a #
Bifoldable (Tagged :: Type -> Type -> Type) # |
Instance details Defined in Data.Tagged Methods bifold :: Monoid m => Tagged m m -> m # bifoldMap :: Monoid m => (a -> m) -> (b -> m) -> Tagged a b -> m # bifoldr :: (a -> c -> c) -> (b -> c -> c) -> c -> Tagged a b -> c # bifoldl :: (c -> a -> c) -> (c -> b -> c) -> c -> Tagged a b -> c #
Bifoldable1 (Tagged :: Type -> Type -> Type) # |
Instance details Defined in Data.Tagged Methods bifold1 :: Semigroup m => Tagged m m -> m # bifoldMap1 :: Semigroup m => (a -> m) -> (b -> m) -> Tagged a b -> m #
Bifunctor (Tagged :: Type -> Type -> Type) # |
Instance details Defined in Data.Tagged Methods bimap :: (a -> b) -> (c -> d) -> Tagged a c -> Tagged b d # first :: (a -> b) -> Tagged a c -> Tagged b c # second :: (b -> c) -> Tagged a b -> Tagged a c #
Bitraversable (Tagged :: Type -> Type -> Type) # |
Instance details Defined in Data.Tagged Methods bitraverse :: Applicative f => (a -> f c) -> (b -> f d) -> Tagged a b -> f (Tagged c d) #
Eq2 (Tagged :: Type -> Type -> Type) # |
Instance details Defined in Data.Tagged Methods liftEq2 :: (a -> b -> Bool) -> (c -> d -> Bool) -> Tagged a c -> Tagged b d -> Bool #
Ord2 (Tagged :: Type -> Type -> Type) # |
Instance details Defined in Data.Tagged Methods liftCompare2 :: (a -> b -> Ordering) -> (c -> d -> Ordering) -> Tagged a c -> Tagged b d -> Ordering #
Read2 (Tagged :: Type -> Type -> Type) # |
Instance details Defined in Data.Tagged Methods liftReadsPrec2 :: (Int -> ReadS a) -> ReadS [a] -> (Int -> ReadS b) -> ReadS [b] -> Int -> ReadS (Tagged a b) # liftReadList2 :: (Int -> ReadS a) -> ReadS [a] -> (Int -> ReadS b) -> ReadS [b] -> ReadS [Tagged a b] # liftReadPrec2 :: ReadPrec a -> ReadPrec [a] -> ReadPrec b -> ReadPrec [b] -> ReadPrec (Tagged a b) # liftReadListPrec2 :: ReadPrec a -> ReadPrec [a] -> ReadPrec b -> ReadPrec [b] -> ReadPrec [Tagged a b] #
Show2 (Tagged :: Type -> Type -> Type) # |
Instance details Defined in Data.Tagged Methods liftShowsPrec2 :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> (Int -> b -> ShowS) -> ([b] -> ShowS) -> Int -> Tagged a b -> ShowS # liftShowList2 :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> (Int -> b -> ShowS) -> ([b] -> ShowS) -> [Tagged a b] -> ShowS #
Foldable1 (Tagged a) # |
Instance details Defined in Data.Tagged Methods fold1 :: Semigroup m => Tagged a m -> m # foldMap1 :: Semigroup m => (a0 -> m) -> Tagged a a0 -> m # foldMap1' :: Semigroup m => (a0 -> m) -> Tagged a a0 -> m # toNonEmpty :: Tagged a a0 -> NonEmpty a0 # maximum :: Ord a0 => Tagged a a0 -> a0 # minimum :: Ord a0 => Tagged a a0 -> a0 # head :: Tagged a a0 -> a0 # last :: Tagged a a0 -> a0 # foldrMap1 :: (a0 -> b) -> (a0 -> b -> b) -> Tagged a a0 -> b # foldlMap1' :: (a0 -> b) -> (b -> a0 -> b) -> Tagged a a0 -> b # foldlMap1 :: (a0 -> b) -> (b -> a0 -> b) -> Tagged a a0 -> b # foldrMap1' :: (a0 -> b) -> (a0 -> b -> b) -> Tagged a a0 -> b #
Eq1 (Tagged s) # |
Instance details Defined in Data.Tagged Methods liftEq :: (a -> b -> Bool) -> Tagged s a -> Tagged s b -> Bool #
Ord1 (Tagged s) # |
Instance details Defined in Data.Tagged Methods liftCompare :: (a -> b -> Ordering) -> Tagged s a -> Tagged s b -> Ordering #
Read1 (Tagged s) # |
Instance details Defined in Data.Tagged Methods liftReadsPrec :: (Int -> ReadS a) -> ReadS [a] -> Int -> ReadS (Tagged s a) # liftReadList :: (Int -> ReadS a) -> ReadS [a] -> ReadS [Tagged s a] # liftReadPrec :: ReadPrec a -> ReadPrec [a] -> ReadPrec (Tagged s a) # liftReadListPrec :: ReadPrec a -> ReadPrec [a] -> ReadPrec [Tagged s a] #
Show1 (Tagged s) # |
Instance details Defined in Data.Tagged Methods liftShowsPrec :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> Int -> Tagged s a -> ShowS # liftShowList :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> [Tagged s a] -> ShowS #
Applicative (Tagged s) # |
Instance details Defined in Data.Tagged Methods pure :: a -> Tagged s a # (<*>) :: Tagged s (a -> b) -> Tagged s a -> Tagged s b # liftA2 :: (a -> b -> c) -> Tagged s a -> Tagged s b -> Tagged s c # (*>) :: Tagged s a -> Tagged s b -> Tagged s b # (<*) :: Tagged s a -> Tagged s b -> Tagged s a #
Functor (Tagged s) # |
Instance details Defined in Data.Tagged Methods fmap :: (a -> b) -> Tagged s a -> Tagged s b # (<$) :: a -> Tagged s b -> Tagged s a #
Monad (Tagged s) # |
Instance details Defined in Data.Tagged Methods (>>=) :: Tagged s a -> (a -> Tagged s b) -> Tagged s b # (>>) :: Tagged s a -> Tagged s b -> Tagged s b # return :: a -> Tagged s a #
Foldable (Tagged s) # |
Instance details Defined in Data.Tagged Methods fold :: Monoid m => Tagged s m -> m # foldMap :: Monoid m => (a -> m) -> Tagged s a -> m # foldMap' :: Monoid m => (a -> m) -> Tagged s a -> m # foldr :: (a -> b -> b) -> b -> Tagged s a -> b # foldr' :: (a -> b -> b) -> b -> Tagged s a -> b # foldl :: (b -> a -> b) -> b -> Tagged s a -> b # foldl' :: (b -> a -> b) -> b -> Tagged s a -> b # foldr1 :: (a -> a -> a) -> Tagged s a -> a # foldl1 :: (a -> a -> a) -> Tagged s a -> a # toList :: Tagged s a -> [a] # null :: Tagged s a -> Bool # length :: Tagged s a -> Int # elem :: Eq a => a -> Tagged s a -> Bool # maximum :: Ord a => Tagged s a -> a # minimum :: Ord a => Tagged s a -> a # sum :: Num a => Tagged s a -> a # product :: Num a => Tagged s a -> a #
Traversable (Tagged s) # |
Instance details Defined in Data.Tagged Methods traverse :: Applicative f => (a -> f b) -> Tagged s a -> f (Tagged s b) # sequenceA :: Applicative f => Tagged s (f a) -> f (Tagged s a) # mapM :: Monad m => (a -> m b) -> Tagged s a -> m (Tagged s b) # sequence :: Monad m => Tagged s (m a) -> m (Tagged s a) #
NFData b => NFData (Tagged s b) # |
Instance details Defined in Data.Tagged Methods rnf :: Tagged s b -> () #
(Semigroup a, Monoid a) => Monoid (Tagged s a) # |
Instance details Defined in Data.Tagged Methods mempty :: Tagged s a # mappend :: Tagged s a -> Tagged s a -> Tagged s a # mconcat :: [Tagged s a] -> Tagged s a #
Semigroup a => Semigroup (Tagged s a) # |
Instance details Defined in Data.Tagged Methods (<>) :: Tagged s a -> Tagged s a -> Tagged s a # sconcat :: NonEmpty (Tagged s a) -> Tagged s a # stimes :: Integral b => b -> Tagged s a -> Tagged s a #
Bits a => Bits (Tagged s a) # |
Instance details Defined in Data.Tagged Methods (.&.) :: Tagged s a -> Tagged s a -> Tagged s a # (.|.) :: Tagged s a -> Tagged s a -> Tagged s a # xor :: Tagged s a -> Tagged s a -> Tagged s a # complement :: Tagged s a -> Tagged s a # shift :: Tagged s a -> Int -> Tagged s a # rotate :: Tagged s a -> Int -> Tagged s a # zeroBits :: Tagged s a # bit :: Int -> Tagged s a # setBit :: Tagged s a -> Int -> Tagged s a # clearBit :: Tagged s a -> Int -> Tagged s a # complementBit :: Tagged s a -> Int -> Tagged s a # testBit :: Tagged s a -> Int -> Bool # bitSizeMaybe :: Tagged s a -> Maybe Int # bitSize :: Tagged s a -> Int # isSigned :: Tagged s a -> Bool # shiftL :: Tagged s a -> Int -> Tagged s a # unsafeShiftL :: Tagged s a -> Int -> Tagged s a # shiftR :: Tagged s a -> Int -> Tagged s a # unsafeShiftR :: Tagged s a -> Int -> Tagged s a # rotateL :: Tagged s a -> Int -> Tagged s a # rotateR :: Tagged s a -> Int -> Tagged s a # popCount :: Tagged s a -> Int #
FiniteBits a => FiniteBits (Tagged s a) # |
Instance details Defined in Data.Tagged Methods finiteBitSize :: Tagged s a -> Int # countLeadingZeros :: Tagged s a -> Int # countTrailingZeros :: Tagged s a -> Int #
(Data s, Data b) => Data (Tagged s b) # |
Instance details Defined in Data.Tagged Methods gfoldl :: (forall d b0. Data d => c (d -> b0) -> d -> c b0) -> (forall g. g -> c g) -> Tagged s b -> c (Tagged s b) # gunfold :: (forall b0 r. Data b0 => c (b0 -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (Tagged s b) # toConstr :: Tagged s b -> Constr # dataTypeOf :: Tagged s b -> DataType # dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c (Tagged s b)) # dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c (Tagged s b)) # gmapT :: (forall b0. Data b0 => b0 -> b0) -> Tagged s b -> Tagged s b # gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Tagged s b -> r # gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Tagged s b -> r # gmapQ :: (forall d. Data d => d -> u) -> Tagged s b -> [u] # gmapQi :: Int -> (forall d. Data d => d -> u) -> Tagged s b -> u # gmapM :: Monad m => (forall d. Data d => d -> m d) -> Tagged s b -> m (Tagged s b) # gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Tagged s b -> m (Tagged s b) # gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Tagged s b -> m (Tagged s b) #
IsString a => IsString (Tagged s a) # |
Instance details Defined in Data.Tagged Methods fromString :: String -> Tagged s a #
Bounded b => Bounded (Tagged s b) # |
Instance details Defined in Data.Tagged Methods minBound :: Tagged s b # maxBound :: Tagged s b #
Enum a => Enum (Tagged s a) # |
Instance details Defined in Data.Tagged Methods succ :: Tagged s a -> Tagged s a # pred :: Tagged s a -> Tagged s a # toEnum :: Int -> Tagged s a # fromEnum :: Tagged s a -> Int # enumFrom :: Tagged s a -> [Tagged s a] # enumFromThen :: Tagged s a -> Tagged s a -> [Tagged s a] # enumFromTo :: Tagged s a -> Tagged s a -> [Tagged s a] # enumFromThenTo :: Tagged s a -> Tagged s a -> Tagged s a -> [Tagged s a] #
Floating a => Floating (Tagged s a) # |
Instance details Defined in Data.Tagged Methods pi :: Tagged s a # exp :: Tagged s a -> Tagged s a # log :: Tagged s a -> Tagged s a # sqrt :: Tagged s a -> Tagged s a # (**) :: Tagged s a -> Tagged s a -> Tagged s a # logBase :: Tagged s a -> Tagged s a -> Tagged s a # sin :: Tagged s a -> Tagged s a # cos :: Tagged s a -> Tagged s a # tan :: Tagged s a -> Tagged s a # asin :: Tagged s a -> Tagged s a # acos :: Tagged s a -> Tagged s a # atan :: Tagged s a -> Tagged s a # sinh :: Tagged s a -> Tagged s a # cosh :: Tagged s a -> Tagged s a # tanh :: Tagged s a -> Tagged s a # asinh :: Tagged s a -> Tagged s a # acosh :: Tagged s a -> Tagged s a # atanh :: Tagged s a -> Tagged s a # log1p :: Tagged s a -> Tagged s a # expm1 :: Tagged s a -> Tagged s a # log1pexp :: Tagged s a -> Tagged s a # log1mexp :: Tagged s a -> Tagged s a #
RealFloat a => RealFloat (Tagged s a) # |
Instance details Defined in Data.Tagged Methods floatRadix :: Tagged s a -> Integer # floatDigits :: Tagged s a -> Int # floatRange :: Tagged s a -> (Int, Int) # decodeFloat :: Tagged s a -> (Integer, Int) # encodeFloat :: Integer -> Int -> Tagged s a # exponent :: Tagged s a -> Int # significand :: Tagged s a -> Tagged s a # scaleFloat :: Int -> Tagged s a -> Tagged s a # isNaN :: Tagged s a -> Bool # isInfinite :: Tagged s a -> Bool # isDenormalized :: Tagged s a -> Bool # isNegativeZero :: Tagged s a -> Bool # isIEEE :: Tagged s a -> Bool # atan2 :: Tagged s a -> Tagged s a -> Tagged s a #
Storable a => Storable (Tagged s a) # |
Instance details Defined in Data.Tagged Methods sizeOf :: Tagged s a -> Int # alignment :: Tagged s a -> Int # peekElemOff :: Ptr (Tagged s a) -> Int -> IO (Tagged s a) # pokeElemOff :: Ptr (Tagged s a) -> Int -> Tagged s a -> IO () # peekByteOff :: Ptr b -> Int -> IO (Tagged s a) # pokeByteOff :: Ptr b -> Int -> Tagged s a -> IO () # peek :: Ptr (Tagged s a) -> IO (Tagged s a) # poke :: Ptr (Tagged s a) -> Tagged s a -> IO () #
Generic (Tagged s b) # |
Instance details Defined in Data.Tagged Associated Types
type Rep (Tagged s b) |
Instance details Defined in Data.Tagged type Rep (Tagged s b) = D1 ('MetaData "Tagged" "Data.Tagged" "tagged-0.8.9-DfMvf7f6neV1YEOofSyVFB" 'True) (C1 ('MetaCons "Tagged" 'PrefixI 'True) (S1 ('MetaSel ('Just "unTagged") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 b)))
Methods from :: Tagged s b -> Rep (Tagged s b) x # to :: Rep (Tagged s b) x -> Tagged s b #
Ix b => Ix (Tagged s b) # |
Instance details Defined in Data.Tagged Methods range :: (Tagged s b, Tagged s b) -> [Tagged s b] # index :: (Tagged s b, Tagged s b) -> Tagged s b -> Int # unsafeIndex :: (Tagged s b, Tagged s b) -> Tagged s b -> Int # inRange :: (Tagged s b, Tagged s b) -> Tagged s b -> Bool # rangeSize :: (Tagged s b, Tagged s b) -> Int # unsafeRangeSize :: (Tagged s b, Tagged s b) -> Int #
Num a => Num (Tagged s a) # |
Instance details Defined in Data.Tagged Methods (+) :: Tagged s a -> Tagged s a -> Tagged s a # (-) :: Tagged s a -> Tagged s a -> Tagged s a # (*) :: Tagged s a -> Tagged s a -> Tagged s a # negate :: Tagged s a -> Tagged s a # abs :: Tagged s a -> Tagged s a # signum :: Tagged s a -> Tagged s a # fromInteger :: Integer -> Tagged s a #
Read b => Read (Tagged s b) # |
Instance details Defined in Data.Tagged Methods readsPrec :: Int -> ReadS (Tagged s b) # readList :: ReadS [Tagged s b] # readPrec :: ReadPrec (Tagged s b) # readListPrec :: ReadPrec [Tagged s b] #
Fractional a => Fractional (Tagged s a) # |
Instance details Defined in Data.Tagged Methods (/) :: Tagged s a -> Tagged s a -> Tagged s a # recip :: Tagged s a -> Tagged s a # fromRational :: Rational -> Tagged s a #
Integral a => Integral (Tagged s a) # |
Instance details Defined in Data.Tagged Methods quot :: Tagged s a -> Tagged s a -> Tagged s a # rem :: Tagged s a -> Tagged s a -> Tagged s a # div :: Tagged s a -> Tagged s a -> Tagged s a # mod :: Tagged s a -> Tagged s a -> Tagged s a # quotRem :: Tagged s a -> Tagged s a -> (Tagged s a, Tagged s a) # divMod :: Tagged s a -> Tagged s a -> (Tagged s a, Tagged s a) # toInteger :: Tagged s a -> Integer #
Real a => Real (Tagged s a) # |
Instance details Defined in Data.Tagged Methods toRational :: Tagged s a -> Rational #
RealFrac a => RealFrac (Tagged s a) # |
Instance details Defined in Data.Tagged Methods properFraction :: Integral b => Tagged s a -> (b, Tagged s a) # truncate :: Integral b => Tagged s a -> b # round :: Integral b => Tagged s a -> b # ceiling :: Integral b => Tagged s a -> b # floor :: Integral b => Tagged s a -> b #
Show b => Show (Tagged s b) # |
Instance details Defined in Data.Tagged Methods showsPrec :: Int -> Tagged s b -> ShowS # show :: Tagged s b -> String # showList :: [Tagged s b] -> ShowS #
Eq b => Eq (Tagged s b) # |
Instance details Defined in Data.Tagged Methods (==) :: Tagged s b -> Tagged s b -> Bool # (/=) :: Tagged s b -> Tagged s b -> Bool #
Ord b => Ord (Tagged s b) # |
Instance details Defined in Data.Tagged Methods compare :: Tagged s b -> Tagged s b -> Ordering # (<) :: Tagged s b -> Tagged s b -> Bool # (<=) :: Tagged s b -> Tagged s b -> Bool # (>) :: Tagged s b -> Tagged s b -> Bool # (>=) :: Tagged s b -> Tagged s b -> Bool # max :: Tagged s b -> Tagged s b -> Tagged s b # min :: Tagged s b -> Tagged s b -> Tagged s b #
type Rep1 (Tagged s :: Type -> Type) # |
Instance details Defined in Data.Tagged type Rep1 (Tagged s :: Type -> Type) = D1 ('MetaData "Tagged" "Data.Tagged" "tagged-0.8.9-DfMvf7f6neV1YEOofSyVFB" 'True) (C1 ('MetaCons "Tagged" 'PrefixI 'True) (S1 ('MetaSel ('Just "unTagged") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) Par1))
type Rep (Tagged s b) # |
Instance details Defined in Data.Tagged type Rep (Tagged s b) = D1 ('MetaData "Tagged" "Data.Tagged" "tagged-0.8.9-DfMvf7f6neV1YEOofSyVFB" 'True) (C1 ('MetaCons "Tagged" 'PrefixI 'True) (S1 ('MetaSel ('Just "unTagged") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 b)))

retag :: forall {k1} {k2} (s :: k1) b (t :: k2). Tagged s b -> Tagged t b #

Some times you need to change the tag you have lying around. Idiomatic usage is to make a new combinator for the relationship between the tags that you want to enforce, and define that combinator using `retag`.

    data Succ n
    retagSucc :: Tagged n a -> Tagged (Succ n) a
    retagSucc = retag

untag :: forall {k} (s :: k) b. Tagged s b -> b #

Alias for `unTagged`

tagSelf :: a -> Tagged a a #

Tag a value with its own type.

untagSelf :: Tagged a a -> a #

`untagSelf` is a type-restricted version of `untag`.

asTaggedTypeOf :: forall {k} s tagged (b :: k). s -> tagged s b -> s #

`asTaggedTypeOf` is a type-restricted version of `const`. It is usually used as an infix operator, and its typing forces its first argument (which is usually overloaded) to have the same type as the tag of the second.

witness :: Tagged a b -> a -> b #

# Conversion

proxy :: forall {k} (s :: k) a proxy. Tagged s a -> proxy s -> a #

Convert from a `Tagged` representation to a representation based on a `Proxy`.

unproxy :: forall {k} (s :: k) a. (Proxy s -> a) -> Tagged s a #

Convert from a representation based on a `Proxy` to a `Tagged` representation.

tagWith :: forall {k} proxy (s :: k) a. proxy s -> a -> Tagged s a #

Another way to convert a proxy to a tag.

# Proxy methods GHC dropped

reproxy :: forall {k1} {k2} proxy (a :: k1) (b :: k2). proxy a -> Proxy b #

Some times you need to change the proxy you have lying around. Idiomatic usage is to make a new combinator for the relationship between the proxies that you want to enforce, and define that combinator using `reproxy`.

    data Succ n
    reproxySucc :: proxy n -> Proxy (Succ n)
    reproxySucc = reproxy