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GHC 10.0.0.20260917 · lts/ghc-10.0.x · 8fef28d · 2026-11-02

Moduletype-hint-0.1Haskell2010

Type.Hint

This module provides Proxy values for various types from the base library and functions to use these values as hints for type inference.

Contents

Hinting functions
Standard types proxies

Synopsis

Packagetype-hint-0.1
Exports56
LanguageHaskell2010
LicenceBSD-3-Clause
SourceHint.hs

Hinting functions

valuehintType :: α -> p α -> α

Hint the type system about the type.

valuehintType1 :: f α -> p f -> f α

Hint the type system about the type constructor.

valuehintTypeArg :: f α -> p α -> f α

Hint the type system about the type argument.

valuehintType2 :: f α β -> p f -> f α β

Hint the type system about the two-argument type constructor.

valuehintType2Arg1 :: f α β -> p α -> f α β

Hint the type system about the first type argument.

valuehintType2Arg2 :: f α β -> p β -> f α β

Hint the type system about the second type argument.

valuehintType3 :: f α β γ -> p f -> f α β γ

Hint the type system about the three-argument type constructor.

valuehintType3Arg1 :: f α β γ -> p α -> f α β γ

Hint the type system about the first type argument.

valuehintType3Arg2 :: f α β γ -> p β -> f α β γ

Hint the type system about the second type argument.

valuehintType3Arg3 :: f α β γ -> p γ -> f α β γ

Hint the type system about the third type argument.

Standard types proxies

datadata Proxy (t :: 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.

Example1 expression

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

Proxy can even hold types of higher kinds,

Example1 expression

>>> Proxy :: Proxy EitherProxy

Example1 expression

>>> Proxy :: Proxy FunctorProxy

Example1 expression

>>> Proxy :: Proxy complicatedStructureProxy

Instances27Generic1, Monad, Functor, Applicative, Foldable, Traversable, …

Generic1 ProxyDefined in ghc-internal-10.0.0 · GHC.Internal.Generics
Monad ProxyDefined in ghc-internal-10.0.0 · GHC.Internal.Data.Proxy
Functor ProxyDefined in ghc-internal-10.0.0 · GHC.Internal.Data.Proxy
Applicative ProxyDefined in ghc-internal-10.0.0 · GHC.Internal.Data.Proxy
Foldable ProxyDefined in ghc-internal-10.0.0 · GHC.Internal.Data.Foldable
Traversable ProxyDefined in ghc-internal-10.0.0 · GHC.Internal.Data.Traversable
Alternative ProxyDefined in ghc-internal-10.0.0 · GHC.Internal.Data.Proxy
MonadPlus ProxyDefined in ghc-internal-10.0.0 · GHC.Internal.Data.Proxy
MonadZip ProxyDefined in ghc-internal-10.0.0 · GHC.Internal.Control.Monad.Zip
Eq1 ProxyDefined in base-4.23.0.0 · Data.Functor.Classes
Ord1 ProxyDefined in base-4.23.0.0 · Data.Functor.Classes
Read1 ProxyDefined in base-4.23.0.0 · Data.Functor.Classes
Show1 ProxyDefined in base-4.23.0.0 · Data.Functor.Classes
Contravariant ProxyDefined in base-4.23.0.0 · Data.Functor.Contravariant
Bounded (Proxy t)Defined in ghc-internal-10.0.0 · GHC.Internal.Data.Proxy
Enum (Proxy s)Defined in ghc-internal-10.0.0 · GHC.Internal.Data.Proxy
Eq (Proxy s)Defined in ghc-internal-10.0.0 · GHC.Internal.Data.Proxy
Data t => Data (Proxy t)Defined in ghc-internal-10.0.0 · GHC.Internal.Data.Data
Ord (Proxy s)Defined in ghc-internal-10.0.0 · GHC.Internal.Data.Proxy
Read (Proxy t)Defined in ghc-internal-10.0.0 · GHC.Internal.Data.Proxy
Show (Proxy s)Defined in ghc-internal-10.0.0 · GHC.Internal.Data.Proxy
Ix (Proxy s)Defined in ghc-internal-10.0.0 · GHC.Internal.Data.Proxy
Generic (Proxy t)Defined in ghc-internal-10.0.0 · GHC.Internal.Generics
Semigroup (Proxy s)Defined in ghc-internal-10.0.0 · GHC.Internal.Data.Proxy
Monoid (Proxy s)Defined in ghc-internal-10.0.0 · GHC.Internal.Data.Proxy
type Rep (Proxy t) = D1 ('MetaData "Proxy" "GHC.Internal.Data.Proxy" "ghc-internal" 'False) (C1 ('MetaCons "Proxy" 'PrefixI 'False) U1)Defined in ghc-internal-10.0.0 · GHC.Internal.Generics
type Rep1 Proxy = D1 ('MetaData "Proxy" "GHC.Internal.Data.Proxy" "ghc-internal" 'False) (C1 ('MetaCons "Proxy" 'PrefixI 'False) U1)Defined in ghc-internal-10.0.0 · GHC.Internal.Generics

valueaUnit :: Proxy ()

() proxy value.

valueaChar :: Proxy Char

Char proxy value.

valueanInteger :: Proxy Integer

Integer proxy value.

valueanInt :: Proxy Int

Int proxy value.

valueanInt8 :: Proxy Int8

Int8 proxy value.

valueanInt16 :: Proxy Int16

Int16 proxy value.

valueanInt32 :: Proxy Int32

Int32 proxy value.

valueanInt64 :: Proxy Int64

Int64 proxy value.

valueaWord :: Proxy Word

Word proxy value.

valueaWord8 :: Proxy Word8

Word8 proxy value.

valueaWord16 :: Proxy Word16

Word16 proxy value.

valueaWord32 :: Proxy Word32

Word32 proxy value.

valueaWord64 :: Proxy Word64

Word64 proxy value.

valueaRatio :: Proxy Ratio

Ratio proxy value.

valueaRatioOf :: Proxy α -> Proxy (Ratio α)

Ratio α proxy value.

valueaRational :: Proxy Rational

Rational proxy value.

valueaFixed :: Proxy Fixed

Fixed proxy value.

valueaFixedOf :: Proxy α -> Proxy (Fixed α)

Fixed α proxy value.

valueaUni :: Proxy Uni

Uni proxy value.

valueaDeci :: Proxy Deci

Deci proxy value.

valueaCenti :: Proxy Centi

Centi proxy value.

valueaMilli :: Proxy Milli

Milli proxy value.

valueaMicro :: Proxy Micro

Micro proxy value.

valueaNano :: Proxy Nano

Nano proxy value.

valueaPico :: Proxy Pico

Pico proxy value.

valueaFloat :: Proxy Float

Float proxy value.

valueaDouble :: Proxy Double

Double proxy value.

valueaMaybe :: Proxy Maybe

Maybe proxy value.

valueaMaybeOf :: Proxy α -> Proxy (Maybe α)

Maybe α proxy value.

valueaPair :: Proxy Tuple2

Pair proxy value.

valueaPairOf :: Proxy α -> Proxy β -> Proxy (α, β)

(α, β) proxy value.

valueaTriple :: Proxy Tuple3

Triple proxy value.

valueaTripleOf :: Proxy α -> Proxy β -> Proxy γ -> Proxy (α, β, γ)

(α, β, γ) proxy value.

valueanEither :: Proxy Either

Either proxy value.

valueanEitherOf :: Proxy α -> Proxy β -> Proxy (Either α β)

Either α β proxy value.

valueaList :: Proxy []

List proxy value.

valueaListOf :: Proxy α -> Proxy [α]

List of α proxy value.

valueanIo :: Proxy IO

IO proxy value.

valueanIoOf :: Proxy α -> Proxy (IO α)

IO α proxy value.

valueanIoRef :: Proxy IORef

IORef proxy value.

valueanIoRefOf :: Proxy α -> Proxy (IORef α)

IORef α proxy value.

valueanSt :: Proxy ST

ST proxy value.

valueanStOf :: Proxy α -> Proxy (ST α)

ST α proxy value.

valueanStRef :: Proxy STRef

STRef proxy value.

valueanStRefOf :: Proxy α -> Proxy (STRef α)

STRef α proxy value.