[Haskell-cafe] [ANN] singletons-3.0, singletons-th-3.0, and singletons-base-3.0

Fri Mar 12 17:38:27 UTC 2021

This is fantastic!

On Fri, Mar 12, 2021 at 12:31 PM Ryan Scott <ryan.gl.scott at gmail.com> wrote:

> I'm happy to announce the 3.0 release of the singletons library, as
> well as the debut of its companion libraries, singletons-th and
> singletons-base. There's been a fair bit of improvements, cleanup, and
> reorganization since the last release, so I thought it appropriate to
> give this release a super-major version bump. This announcement will
> go over some highlights of the new releases, but if you want the full
> details, you can consult the changelog entries for each library below:
>
> * singletons-3.0:
> http://hackage.haskell.org/package/singletons-3.0/changelog
> * singletons-th-3.0:
> http://hackage.haskell.org/package/singletons-th-3.0/changelog
> * singletons-base-3.0:
> http://hackage.haskell.org/package/singletons-base-3.0/changelog
>
> ##########################
> ## Why three libraries? ##
> ##########################
>
> Instead of there just being one singletons library, there are now
> _three_ libraries:
>
> * singletons: A small, foundational library that defines basic
> singleton-related types and definitions. The new singletons library
> supports GHC 8.0 or later, does not depend on any external libraries,
> and does not make use of Template Haskell.
> * singletons-th: A library that defines Template Haskell functionality
> for promoting term-level functions to type-level equivalents and
> singling functions to dependently typed equivalents. This library
> requires bleeding-edge GHC features, and as a result, it only supports
> GHC 9.0 or later.
> * singletons-base: A library that uses singletons-th to define
> promoted and singled functions from the base library, including the
> Prelude. Similarly to singletons-th, this library only supports GHC
> 9.0 or later.
>
> Previous singletons releases combined all of this functionality into a
> single library. However, discussions with singletons users revealed
> that this was a frequent source of pain:
>
> * The total time it took to compile the old singletons library
> dissuaded some from using it, especially for those who only wanted to
> use a small part of the library.
> * Some users wished to use singletons in environments where Template
> Haskell is not an option.
> * Some users wanted to use core definitions from Data.Singletons, but
> because the old singletons library only ever supported one GHC at a
> time, this was impractical.
>
> The new package structure in the 3.0 release is an attempt to address
> some of these pain points. In particular, most of the code which
> results in extensive compile times is now confined to the
> singletons-base library. For the full discussion that led up to this,
> see [1].
>
> ###########################
> ## Module reorganization ##
> ###########################
>
> Splitting up singletons into smaller packages provided a rare
> opportunity to clean up the module naming conventions, which were
> confusing and inconsistent in many places. The 3.0 releases now use
> the following conventions:
>
> * All modules in singletons now begin with Data.Singletons.*.
> * All modules in singletons-th now begin with Data.Singletons.TH.*.
> * Most modules in singletons-base now reflect the modules from base
> from which they take inspiration. For example, the Prelude module now
> has a Prelude.Singletons counterpart in singletons. Similarly, there
> are also modules like Control.Monad.Singletons,
> GHC.TypeLits.Singletons, etc. All other modules that do not correspond
> to something in base now begin with Data.Singletons.Base.*.
>
> The convention now used in singletons-base was inspired by the
> conventions used in the lens library. The end result is that is now
> somewhat easier to figure out what parts of singletons-base to import.
> Because this is a significant departure from previous singletons
> releases, if you want to continue supporting pre-3.0 releases, you
> will likely need to put something like this in your .cabal file:
>
>     flag singletons-3-0
>       description:         Use @singletons-3.0@ or later.
>       default:             True
>
>     library
>       ...
>       if flag(singletons-3-0)
>         build-depends:
>           singletons-base >= 3.0
>           -- You may also need to depend on singletons >= 3.0 or
> singletons-th >= 3.0
>       else
>         build-depends:
>           singletons < 3.0
>
> ###################
> ## Other changes ##
> ###################
>
> Besides the package and module reorganization mentioned above,
> singletons-{,th,base}-3.0 feature a variety of new quality-of-life
> improvements. Here are a handful of the more notable improvements:
>
> * The OptionsM type, used for configuring how the Template Haskell
> machinery in singletons-th works, is now an instance of Quote. This
> avoids the need to use the Control.Monad.Trans.Class.lift function to
> lift quoted declarations into OptionsM. [2]
> * Data.Singletons.TH.Options now defines a promotedDataTypeOrConName
> option. Overriding this option can be useful in situations where one
> wishes to promote types such as `Nat`, `Symbol`, or data types built
> on top of them. [3]
> * The internals of the ShowSing class have been refactored to allow
> deriving Show instances for Sing types (e.g., deriving instance
> ShowSing a => Show (SList (z :: [a]))). [4]
> * Improve the quality of GHCi's output when using :kind on types
> defined by singletons-th. [5]
>
> If you encounter any issues, feel free to leave a bug report at
> https://github.com/goldfirere/singletons/issues.
>
> Happy (type-level) hacking,
>
> Ryan S.
> -----
> [1] https://github.com/goldfirere/singletons/issues/420
> [2] https://github.com/goldfirere/singletons/pull/484
> [3] https://github.com/goldfirere/singletons/pull/462
> [4] https://github.com/goldfirere/singletons/pull/486
> [5] https://github.com/goldfirere/singletons/pull/446
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/haskell-cafe/attachments/20210312/4bb00f99/attachment.html>