lift-generics

GHC.Generics-based Language.Haskell.TH.Syntax.lift implementation

https://github.com/RyanGlScott/lift-generics

Version on this page:0.2.1
LTS Haskell 18.18:0.2.1@rev:1
Stackage Nightly 2021-11-28:0.2.1@rev:1
Latest on Hackage:0.2.1@rev:1

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BSD-3-Clause licensed by Ryan Scott
Maintained by Ryan Scott
This version can be pinned in stack with:lift-generics-0.2.1@sha256:65355d291494917cac98a241ca72ae4b11a9a313d86a994382715d39bf8bfa26,4398

Module documentation for 0.2.1

lift-generics

Haskell Programming Language Hackage Dependencies Haskell Programming Language BSD3 License Build Status

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.

Credit goes to Matthew Pickering for suggesting this idea.

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.

0.1.1

  • Fix test suite on GHC 8.0

0.1

  • Initial commit