Safe Haskell	Safe-Inferred
Language	Haskell2010

Data.Primitive.Unlifted.Box

Description

Traditionally, there were only a few basic unlifted types available in GHC, all of them primitive. Now, with the UnliftedNewtypes and UnliftedDatatypes extensions, users are free to create as many as they like. However, many essential facilities, like the Monad class, still work only with lifted types, so users must wrap their unlifted types into lifted ones to use those. If the wrapped version of a type is likely to be used heavily on its own, it often makes sense to write a custom wrapper type for it. This module exports a general box for situations where the focus should be on the unlifted type rather than its wrapper.

Synopsis

data Box (a :: UnliftedType) = Box# {
- unBox# :: a
}
toBox :: PrimUnlifted a => a -> Box (Unlifted a)
fromBox :: PrimUnlifted a => Box (Unlifted a) -> a

Documentation

data Box (a :: UnliftedType) Source #

Turn an arbitrary unlifted type into a lifted one with a PrimUnlifted instance. For example, given

data UnliftedMaybe a :: UnliftedType where
  UnliftedNothing :: UnliftedMaybe a
  UnliftedJust :: a -> UnliftedMaybe a

we have

Box (UnliftedMaybe a) :: Type

Constructors

Box#
Fields unBox# :: a

Instances

Instances details

PrimUnlifted (Box a) Source #
Instance details Defined in Data.Primitive.Unlifted.Box Associated Types type Unlifted (Box a) :: UnliftedType Source # Methods toUnlifted# :: Box a -> Unlifted (Box a) Source # fromUnlifted# :: Unlifted (Box a) -> Box a Source #
type Unlifted (Box a) Source #
Instance details Defined in Data.Primitive.Unlifted.Box type Unlifted (Box a) = a

toBox :: PrimUnlifted a => a -> Box (Unlifted a) Source #

fromBox :: PrimUnlifted a => Box (Unlifted a) -> a Source #