LiftType

Template Haskell has a class Lift that allows you to promote values from Haskell-land into the land of metaprogramming - Q.

class Lift a where
    lift :: a -> Q Exp

    liftTyped :: a -> Q (TExp a)

However, there wasn't a way to promote a *type* into a Q Type.

This library provides exactly that function. It requires a Typeable constraint, but this is automatically satisfied by GHC.

Since: 0.1.0.0

Documentation

liftType :: forall t. Typeable t => Type

Convert a type argument into a Template Haskell Type.

Use with TypeApplications.

Example:

>>> :set -XTypeApplications
>>> liftType @Bool
ConT GHC.Types.Bool
>>> liftType @[Char]
AppT (ConT GHC.Types.[]) (ConT GHC.Types.Char)

This works with data kinds, too.

>>> :set -XDataKinds
>>> liftType @3
LitT (NumTyLit 3)
>>> liftType @"hello"
LitT (StrTyLit "hello")
>>> liftType @'[Int, Char]
AppT (AppT (PromotedT GHC.Types.:) (ConT GHC.Types.Int)) (AppT (AppT (PromotedT GHC.Types.:) (ConT GHC.Types.Char)) (PromotedT GHC.Types.[]))
>>> liftType @'(Int, Char)
AppT (AppT (PromotedT GHC.Tuple.(,)) (ConT GHC.Types.Int)) (ConT GHC.Types.Char)

Since: 0.1.0.0

liftTypeQ :: forall t. Typeable t => Q Type

liftType promoted to the Q monad.

Since: 0.1.0.0

typeRepToType :: SomeTypeRep -> Type

Promote a SomeTypeRep into a Type.

Since: 0.1.1.0

tyConToName :: TyCon -> TypeOrDataName

Extract the TypeOrDataName from a TyCon. You probably want to use typeToName instead. See that function for documentation and more information.

Since: 0.1.2.0

typeToName :: forall t. Typeable t => TypeOrDataName

This function returns the name of the outermost type constructor.

>>> typeToName @Char
TypeName ''Char
>>> typeToName @Maybe
TypeName ''Maybe
>>> typeToName @(Maybe Char)
TypeName ''Maybe
>>> typeToName @(Int -> Char)
TypeName ''(->)
>>> typeToName @'False
PromotedDataName 'False

Since: 0.1.2.0

data TypeOrDataName

It's possible to use a data constructor with a DataKinds promotion. This disambiguates where the name comes from.

Since: 0.1.2.0

Constructors

TypeName Name

PromotedDataName Name

Instances

Show TypeOrDataName

Defined in LiftType

Methods

showsPrec :: Int -> TypeOrDataName -> ShowS

show :: TypeOrDataName -> String

showList :: [TypeOrDataName] -> ShowS

Eq TypeOrDataName

Defined in LiftType

Methods

(==) :: TypeOrDataName -> TypeOrDataName -> Bool

(/=) :: TypeOrDataName -> TypeOrDataName -> Bool

getTypeOrDataName :: TypeOrDataName -> Name

Retrieve the Name from a TypeOrDataName, forgetting how it was parsed.

Since: 0.1.2.0