Proposal: Make `NFData` a fundamental/primitive type-class (by making `deepseq` a GHC-boot package)

[Edward Kmett]

+1

Sent from my iPhone

On Aug 23, 2011, at 7:39 AM, Herbert Valerio Riedel <hvr at gnu.org> wrote:

> Proposal:
> ~~~~~~~~~
> 
> Make `NFData` a fundamental/primitive type-class
> (by making `deepseq` a GHC-boot package)
> 
> Discussion deadline: 2 weeks.
> 
> Note: This is a reboot of a previous unresolved proposal[1] by Johan Tibell
> with a slightly different emphasis.
> 
> Current Issues:
> ~~~~~~~~~~~~~~~
> 
> - The `deepseq` package should not depend on `containers` and `array`
>   (ideally `deepseq` would be merged with `base` and
>   `containers`/`array` would define their own `NFData` instances)
> 
> - Not all data types defined by "core libraries" have `NFData` instances
>   defined (e.g. `time` and `bytestring`). The lack of such "standard"
>   instances causes users of `deepseq` to define local orphan instances
> 
> - GHC boot packages can't depend on `deepseq` as it is not a GHC-boot 
>   package yet, and thus orphan instances are required for those
>   packages -- which would benefit in terms of maintainability[4] and 
>   efficiency[3] from being defined locally by having access to the
>   internal representations
> 
> Rationale:
> ~~~~~~~~~~
> 
> The principal idea this proposal is based upon is that the `NFData`
> type-class is similarly universal/basic/fundamental as the `Ord`,
> `Show`, or `Eq` type-classes are -- it might be even desirable to make
> `NFData` part of a future Haskell Prelude at some point and maybe even
> allow automatic instance derivation.
> 
> 
> Building on this idea that `NFData` is a "primitive" type-class, the
> next best thing that can be done relatively easy and short-term as a
> transitional step is to
> 
> 1) make `deepseq` a GHC-boot package[2],
> 
> 2) remove `deepseq`'s dependancy on `array` and `containers`,
> 
> 3) move the affected instance definitions to the `array` and
>    `containers` packages respectively, and
> 
> 4) satisfy the PVP by incrementing package versions where necessary.
> 
> This should provide a path of least resistance, as no packages
> depending on `deepseq` would have to be adapted except for maybe
> PVP-related version constraint widening.
> 
> 
> Moreover, this would pave the way for a future proposal to merge the
> `deepseq` into `base` at some later point.
> 
> 
> References:
> ~~~~~~~~~~~
> 
> [1]: http://hackage.haskell.org/trac/ghc/ticket/4868
> [2]: http://www.haskell.org/pipermail/libraries/2010-December/015427.html
> [3]: http://www.haskell.org/pipermail/libraries/2010-December/015428.html
> [4]: http://www.haskell.org/pipermail/libraries/2011-January/015488.html
> 
> 
> -- hvr
> 
> 
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