Proposal: Make `NFData` a fundamental/primitive type-class (by making `deepseq` a GHC-boot package)
Herbert Valerio Riedel
hvr at gnu.org
Tue Aug 23 13:39:30 CEST 2011
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 by Johan Tibell
with a slightly different emphasis.
- 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 and
efficiency from being defined locally by having access to the
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) 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.
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