This package provides a GHC.Generics-based genericLiftWithPkg function (intended for GHC 7.10 and earlier), as well as a genericLift function (only available on GHC 8.0 and later), both of which can be used for providing a Language.Haskell.TH.Syntax.lift implementation. See the documentation in the Language.Haskell.TH.Lift.Generics module to get started.
Note that due to API limitations, GHC.Generics wasn’t powerful enough to come up with the entirety of a lift implementation prior to GHC 8.0. For this reason, genericLiftWithPkg requires you to produce the package name yourself, which proves to be no small feat (see the documentation for more info).
Luckily, you don’t have to jump through as many hoops on GHC 8.0 and later: simply use the genericLift function, and life is good.
Changes
0.2.1 [2021.09.16]
The lifting functions have been modified to reduce splice
time for constructors with many fields from quadratic to
linear. This probably only has a modest impact on total
compilation time.
genericLift, genericLiftTyped, genericLiftTypedExp, and
genericLiftTypedCompat functions now work for GHC 7.4 and above
for types that derive Typeable.
genericLiftWithPkgFallback, genericLiftTypedWithPkgFallback,
genericLiftTypedExpWithPkgFallback, and
genericLiftTypedCompatWithPkgFallback functions have been added that take
advantage of Typeable instances for GHC 7.4 and above but also take a
user-provided package name for earlier versions.
0.2 [2020.09.30]
genericLiftTyped and genericLiftTypedWithPkg now return a Code instead
of a TExp to reflect the type of liftTyped changing in
template-haskell-2.17.0.0. New functions genericLiftTypedTExp and
genericLiftTypedTExpWithPkg have been added for those who wish to return
TExp specifically. In addition, the functions genericLiftTypedCompat and
genericLiftTypedCompatWithPkg have been introduced which return a Code
on template-haskell-2.17.0.0 or later, but a TExp on older versions of
template-haskell. These functions are most useful for implementing
liftTyped in a Lift instance in a backwards-compatible way.
The th-compat library is used to backport the Code data type back to
versions of template-haskell that do not define it.
The functions in Language.Haskell.TH.Lift.Generics are now generalized to
work over any Quote instance instead of hardcoding Q. Again, the
th-compat library is used to backport Quote to old versions of
template-haskell that do not define it.
Make genericLift work properly for empty data types.
0.1.3 [2019.11.26]
Add genericLiftTyped and genericLiftTypedWithPkg.
0.1.2
Add a case for V1 (i.e., empty data types), which diverges in the way
you’d expect.
