unboxed

This is a small package exploring how to overload Prelude typeclasses to work over multiple RuntimeReps.

The end result is that with enough extensions, including NoImplicitPrelude, and RebindableSyntax, importing Unlifted.Prelude will allow you to work with Eq, Ord, Num, etc. in any TYPE r, not just TYPE 'LiftedRep. This allows using numeric literals such as 3 in unlifted types such as Int#, or Float#. If you are working with types of kind Type, this package will delegate to normal Prelude instances, so you don't have to provide duplicate definitions.

In addition to overloading classes, some limited data types are also offered. Notably lists of lifted or unboxed values, and lifted and unlifted Maybes of lifted or unlifted values. When GHC 9.2 lands, hopefully with support for unboxed data types, then an unlifted list should be possible.

The key operation to allow this is Lev in Unlifted.Levitation. It can be used to adapt any TYPE r to Type in negative position, by observing that in core, any constrained type is in Type and attaching a trivial constraint.

This allows ifThenElse to work under RebindableSyntax at all TYPE r types, despite levity polymorphism not allowing its use in negative position, and for the if to be appropriately lazy.

If you are going to explore the library using the ghci, I'd recommend running ghci with -fno-it to keep it from trying to bing the last variable, given it can't bind unlifted variables. Running with -interactive-print print will use whatever defininition of print is in scope, and the one in Unlifted.Prelude is sufficiently polymorphic to work with lifted and unlifted values. See the comments in the local .ghci file.

There are a lot of classes in base that should be ported, and many hands make for light work, so please feel free to pitch in!

License

Licensed under either of

• Apache License, Version 2.0 (http://www.apache.org/licenses/LICENSE-2.0)
• BSD 2-Clause license (https://opensource.org/licenses/BSD-2-Clause) at your option.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you shall be dual-licensed as above, without any additional terms or conditions.

Contact Information

Contributions and bug reports are welcome!

Please feel free to contact me through github or on the ##coda or #haskell IRC channels on irc.freenode.net.

-Edward Kmett