planet-mitchell-0.0.0: Planet Mitchell

Safe HaskellSafe
LanguageHaskell2010

Proxy

Synopsis

Documentation

data Proxy (t :: k) :: forall k. k -> * #

Proxy is a type that holds no data, but has a phantom parameter of arbitrary type (or even kind). Its use is to provide type information, even though there is no value available of that type (or it may be too costly to create one).

Historically, Proxy :: Proxy a is a safer alternative to the 'undefined :: a' idiom.

>>> Proxy :: Proxy (Void, Int -> Int)
Proxy

Proxy can even hold types of higher kinds,

>>> Proxy :: Proxy Either
Proxy
>>> Proxy :: Proxy Functor
Proxy
>>> Proxy :: Proxy complicatedStructure
Proxy

Constructors

Proxy 
Instances
Generic1 (Proxy :: k -> *) 
Instance details

Defined in GHC.Generics

Associated Types

type Rep1 Proxy :: k -> * #

Methods

from1 :: Proxy a -> Rep1 Proxy a #

to1 :: Rep1 Proxy a -> Proxy a #

Monad (Proxy :: * -> *)

Since: base-4.7.0.0

Instance details

Defined in Data.Proxy

Methods

(>>=) :: Proxy a -> (a -> Proxy b) -> Proxy b #

(>>) :: Proxy a -> Proxy b -> Proxy b #

return :: a -> Proxy a #

fail :: String -> Proxy a #

Functor (Proxy :: * -> *)

Since: base-4.7.0.0

Instance details

Defined in Data.Proxy

Methods

fmap :: (a -> b) -> Proxy a -> Proxy b #

(<$) :: a -> Proxy b -> Proxy a #

Applicative (Proxy :: * -> *)

Since: base-4.7.0.0

Instance details

Defined in Data.Proxy

Methods

pure :: a -> Proxy a #

(<*>) :: Proxy (a -> b) -> Proxy a -> Proxy b #

liftA2 :: (a -> b -> c) -> Proxy a -> Proxy b -> Proxy c #

(*>) :: Proxy a -> Proxy b -> Proxy b #

(<*) :: Proxy a -> Proxy b -> Proxy a #

Foldable (Proxy :: * -> *)

Since: base-4.7.0.0

Instance details

Defined in Data.Foldable

Methods

fold :: Monoid m => Proxy m -> m #

foldMap :: Monoid m => (a -> m) -> Proxy a -> m #

foldr :: (a -> b -> b) -> b -> Proxy a -> b #

foldr' :: (a -> b -> b) -> b -> Proxy a -> b #

foldl :: (b -> a -> b) -> b -> Proxy a -> b #

foldl' :: (b -> a -> b) -> b -> Proxy a -> b #

foldr1 :: (a -> a -> a) -> Proxy a -> a #

foldl1 :: (a -> a -> a) -> Proxy a -> a #

toList :: Proxy a -> [a] #

null :: Proxy a -> Bool #

length :: Proxy a -> Int #

elem :: Eq a => a -> Proxy a -> Bool #

maximum :: Ord a => Proxy a -> a #

minimum :: Ord a => Proxy a -> a #

sum :: Num a => Proxy a -> a #

product :: Num a => Proxy a -> a #

Traversable (Proxy :: * -> *)

Since: base-4.7.0.0

Instance details

Defined in Data.Traversable

Methods

traverse :: Applicative f => (a -> f b) -> Proxy a -> f (Proxy b) #

sequenceA :: Applicative f => Proxy (f a) -> f (Proxy a) #

mapM :: Monad m => (a -> m b) -> Proxy a -> m (Proxy b) #

sequence :: Monad m => Proxy (m a) -> m (Proxy a) #

Alternative (Proxy :: * -> *)

Since: base-4.9.0.0

Instance details

Defined in Data.Proxy

Methods

empty :: Proxy a #

(<|>) :: Proxy a -> Proxy a -> Proxy a #

some :: Proxy a -> Proxy [a] #

many :: Proxy a -> Proxy [a] #

Distributive (Proxy :: * -> *) 
Instance details

Defined in Data.Distributive

Methods

distribute :: Functor f => f (Proxy a) -> Proxy (f a) #

collect :: Functor f => (a -> Proxy b) -> f a -> Proxy (f b) #

distributeM :: Monad m => m (Proxy a) -> Proxy (m a) #

collectM :: Monad m => (a -> Proxy b) -> m a -> Proxy (m b) #

Contravariant (Proxy :: * -> *) 
Instance details

Defined in Data.Functor.Contravariant

Methods

contramap :: (a -> b) -> Proxy b -> Proxy a #

(>$) :: b -> Proxy b -> Proxy a #

Representable (Proxy :: * -> *) 
Instance details

Defined in Data.Functor.Rep

Associated Types

type Rep Proxy :: * #

Methods

tabulate :: (Rep Proxy -> a) -> Proxy a #

index :: Proxy a -> Rep Proxy -> a #

ToJSON1 (Proxy :: * -> *) 
Instance details

Defined in Data.Aeson.Types.ToJSON

Methods

liftToJSON :: (a -> Value) -> ([a] -> Value) -> Proxy a -> Value #

liftToJSONList :: (a -> Value) -> ([a] -> Value) -> [Proxy a] -> Value #

liftToEncoding :: (a -> Encoding) -> ([a] -> Encoding) -> Proxy a -> Encoding #

liftToEncodingList :: (a -> Encoding) -> ([a] -> Encoding) -> [Proxy a] -> Encoding #

FromJSON1 (Proxy :: * -> *) 
Instance details

Defined in Data.Aeson.Types.FromJSON

Methods

liftParseJSON :: (Value -> Parser a) -> (Value -> Parser [a]) -> Value -> Parser (Proxy a) #

liftParseJSONList :: (Value -> Parser a) -> (Value -> Parser [a]) -> Value -> Parser [Proxy a] #

MonadPlus (Proxy :: * -> *)

Since: base-4.9.0.0

Instance details

Defined in Data.Proxy

Methods

mzero :: Proxy a #

mplus :: Proxy a -> Proxy a -> Proxy a #

Eq1 (Proxy :: * -> *)

Since: base-4.9.0.0

Instance details

Defined in Data.Functor.Classes

Methods

liftEq :: (a -> b -> Bool) -> Proxy a -> Proxy b -> Bool #

Ord1 (Proxy :: * -> *)

Since: base-4.9.0.0

Instance details

Defined in Data.Functor.Classes

Methods

liftCompare :: (a -> b -> Ordering) -> Proxy a -> Proxy b -> Ordering #

Read1 (Proxy :: * -> *)

Since: base-4.9.0.0

Instance details

Defined in Data.Functor.Classes

Methods

liftReadsPrec :: (Int -> ReadS a) -> ReadS [a] -> Int -> ReadS (Proxy a) #

liftReadList :: (Int -> ReadS a) -> ReadS [a] -> ReadS [Proxy a] #

liftReadPrec :: ReadPrec a -> ReadPrec [a] -> ReadPrec (Proxy a) #

liftReadListPrec :: ReadPrec a -> ReadPrec [a] -> ReadPrec [Proxy a] #

Show1 (Proxy :: * -> *)

Since: base-4.9.0.0

Instance details

Defined in Data.Functor.Classes

Methods

liftShowsPrec :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> Int -> Proxy a -> ShowS #

liftShowList :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> [Proxy a] -> ShowS #

MonadZip (Proxy :: * -> *)

Since: base-4.9.0.0

Instance details

Defined in Control.Monad.Zip

Methods

mzip :: Proxy a -> Proxy b -> Proxy (a, b) #

mzipWith :: (a -> b -> c) -> Proxy a -> Proxy b -> Proxy c #

munzip :: Proxy (a, b) -> (Proxy a, Proxy b) #

Divisible (Proxy :: * -> *) 
Instance details

Defined in Data.Functor.Contravariant.Divisible

Methods

divide :: (a -> (b, c)) -> Proxy b -> Proxy c -> Proxy a #

conquer :: Proxy a #

Decidable (Proxy :: * -> *) 
Instance details

Defined in Data.Functor.Contravariant.Divisible

Methods

lose :: (a -> Void) -> Proxy a #

choose :: (a -> Either b c) -> Proxy b -> Proxy c -> Proxy a #

NFData1 (Proxy :: * -> *)

Since: deepseq-1.4.3.0

Instance details

Defined in Control.DeepSeq

Methods

liftRnf :: (a -> ()) -> Proxy a -> () #

Hashable1 (Proxy :: * -> *) 
Instance details

Defined in Data.Hashable.Class

Methods

liftHashWithSalt :: (Int -> a -> Int) -> Int -> Proxy a -> Int #

Apply (Proxy :: * -> *) 
Instance details

Defined in Data.Functor.Bind.Class

Methods

(<.>) :: Proxy (a -> b) -> Proxy a -> Proxy b #

(.>) :: Proxy a -> Proxy b -> Proxy b #

(<.) :: Proxy a -> Proxy b -> Proxy a #

liftF2 :: (a -> b -> c) -> Proxy a -> Proxy b -> Proxy c #

Pointed (Proxy :: * -> *) 
Instance details

Defined in Data.Pointed

Methods

point :: a -> Proxy a #

Plus (Proxy :: * -> *) 
Instance details

Defined in Data.Functor.Plus

Methods

zero :: Proxy a #

Alt (Proxy :: * -> *) 
Instance details

Defined in Data.Functor.Alt

Methods

(<!>) :: Proxy a -> Proxy a -> Proxy a #

some :: Applicative Proxy => Proxy a -> Proxy [a] #

many :: Applicative Proxy => Proxy a -> Proxy [a] #

Bind (Proxy :: * -> *) 
Instance details

Defined in Data.Functor.Bind.Class

Methods

(>>-) :: Proxy a -> (a -> Proxy b) -> Proxy b #

join :: Proxy (Proxy a) -> Proxy a #

Extend (Proxy :: * -> *) 
Instance details

Defined in Data.Functor.Extend

Methods

duplicated :: Proxy a -> Proxy (Proxy a) #

extended :: (Proxy a -> b) -> Proxy a -> Proxy b #

Bounded (Proxy t) 
Instance details

Defined in Data.Proxy

Methods

minBound :: Proxy t #

maxBound :: Proxy t #

Enum (Proxy s)

Since: base-4.7.0.0

Instance details

Defined in Data.Proxy

Methods

succ :: Proxy s -> Proxy s #

pred :: Proxy s -> Proxy s #

toEnum :: Int -> Proxy s #

fromEnum :: Proxy s -> Int #

enumFrom :: Proxy s -> [Proxy s] #

enumFromThen :: Proxy s -> Proxy s -> [Proxy s] #

enumFromTo :: Proxy s -> Proxy s -> [Proxy s] #

enumFromThenTo :: Proxy s -> Proxy s -> Proxy s -> [Proxy s] #

Eq (Proxy s)

Since: base-4.7.0.0

Instance details

Defined in Data.Proxy

Methods

(==) :: Proxy s -> Proxy s -> Bool #

(/=) :: Proxy s -> Proxy s -> Bool #

Data t => Data (Proxy t)

Since: base-4.7.0.0

Instance details

Defined in Data.Data

Methods

gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> Proxy t -> c (Proxy t) #

gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c (Proxy t) #

toConstr :: Proxy t -> Constr #

dataTypeOf :: Proxy t -> DataType #

dataCast1 :: Typeable t0 => (forall d. Data d => c (t0 d)) -> Maybe (c (Proxy t)) #

dataCast2 :: Typeable t0 => (forall d e. (Data d, Data e) => c (t0 d e)) -> Maybe (c (Proxy t)) #

gmapT :: (forall b. Data b => b -> b) -> Proxy t -> Proxy t #

gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Proxy t -> r #

gmapQr :: (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Proxy t -> r #

gmapQ :: (forall d. Data d => d -> u) -> Proxy t -> [u] #

gmapQi :: Int -> (forall d. Data d => d -> u) -> Proxy t -> u #

gmapM :: Monad m => (forall d. Data d => d -> m d) -> Proxy t -> m (Proxy t) #

gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Proxy t -> m (Proxy t) #

gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Proxy t -> m (Proxy t) #

Ord (Proxy s)

Since: base-4.7.0.0

Instance details

Defined in Data.Proxy

Methods

compare :: Proxy s -> Proxy s -> Ordering #

(<) :: Proxy s -> Proxy s -> Bool #

(<=) :: Proxy s -> Proxy s -> Bool #

(>) :: Proxy s -> Proxy s -> Bool #

(>=) :: Proxy s -> Proxy s -> Bool #

max :: Proxy s -> Proxy s -> Proxy s #

min :: Proxy s -> Proxy s -> Proxy s #

Read (Proxy t)

Since: base-4.7.0.0

Instance details

Defined in Data.Proxy

Show (Proxy s)

Since: base-4.7.0.0

Instance details

Defined in Data.Proxy

Methods

showsPrec :: Int -> Proxy s -> ShowS #

show :: Proxy s -> String #

showList :: [Proxy s] -> ShowS #

Ix (Proxy s)

Since: base-4.7.0.0

Instance details

Defined in Data.Proxy

Methods

range :: (Proxy s, Proxy s) -> [Proxy s] #

index :: (Proxy s, Proxy s) -> Proxy s -> Int #

unsafeIndex :: (Proxy s, Proxy s) -> Proxy s -> Int

inRange :: (Proxy s, Proxy s) -> Proxy s -> Bool #

rangeSize :: (Proxy s, Proxy s) -> Int #

unsafeRangeSize :: (Proxy s, Proxy s) -> Int

Generic (Proxy t) 
Instance details

Defined in GHC.Generics

Associated Types

type Rep (Proxy t) :: * -> * #

Methods

from :: Proxy t -> Rep (Proxy t) x #

to :: Rep (Proxy t) x -> Proxy t #

Semigroup (Proxy s)

Since: base-4.9.0.0

Instance details

Defined in Data.Proxy

Methods

(<>) :: Proxy s -> Proxy s -> Proxy s #

sconcat :: NonEmpty (Proxy s) -> Proxy s #

stimes :: Integral b => b -> Proxy s -> Proxy s #

Monoid (Proxy s)

Since: base-4.7.0.0

Instance details

Defined in Data.Proxy

Methods

mempty :: Proxy s #

mappend :: Proxy s -> Proxy s -> Proxy s #

mconcat :: [Proxy s] -> Proxy s #

Hashable (Proxy a) 
Instance details

Defined in Data.Hashable.Class

Methods

hashWithSalt :: Int -> Proxy a -> Int #

hash :: Proxy a -> Int #

ToJSON (Proxy a) 
Instance details

Defined in Data.Aeson.Types.ToJSON

FromJSON (Proxy a) 
Instance details

Defined in Data.Aeson.Types.FromJSON

NFData (Proxy a)

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: Proxy a -> () #

Upper (Proxy a) 
Instance details

Defined in Data.Semilattice.Upper

Methods

upperBound :: Proxy a #

Lower (Proxy a) 
Instance details

Defined in Data.Semilattice.Lower

Methods

lowerBound :: Proxy a #

Serialise (Proxy a)

Since: serialise-0.2.0.0

Instance details

Defined in Codec.Serialise.Class

type Rep1 (Proxy :: k -> *) 
Instance details

Defined in GHC.Generics

type Rep1 (Proxy :: k -> *) = D1 (MetaData "Proxy" "Data.Proxy" "base" False) (C1 (MetaCons "Proxy" PrefixI False) (U1 :: k -> *))
type Rep (Proxy :: * -> *) 
Instance details

Defined in Data.Functor.Rep

type Rep (Proxy :: * -> *) = Void
type Rep (Proxy t) 
Instance details

Defined in GHC.Generics

type Rep (Proxy t) = D1 (MetaData "Proxy" "Data.Proxy" "base" False) (C1 (MetaCons "Proxy" PrefixI False) (U1 :: * -> *))

asProxyTypeOf :: a -> proxy a -> a #

asProxyTypeOf 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.

>>> import Data.Word
>>> :type asProxyTypeOf 123 (Proxy :: Proxy Word8)
asProxyTypeOf 123 (Proxy :: Proxy Word8) :: Word8

Note the lower-case proxy in the definition. This allows any type constructor with just one argument to be passed to the function, for example we could also write

>>> import Data.Word
>>> :type asProxyTypeOf 123 (Just (undefined :: Word8))
asProxyTypeOf 123 (Just (undefined :: Word8)) :: Word8

data KProxy t #

A concrete, promotable proxy type, for use at the kind level There are no instances for this because it is intended at the kind level only

Constructors

KProxy