deriving-compat-0.2: README.md

# `deriving-compat`
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[Hackage: deriving-compat]:
  http://hackage.haskell.org/package/deriving-compat
  "deriving-compat package on Hackage"
[Haskell.org]:
  http://www.haskell.org
  "The Haskell Programming Language"
[tl;dr Legal: BSD3]:
  https://tldrlegal.com/license/bsd-3-clause-license-%28revised%29
  "BSD 3-Clause License (Revised)"

Provides Template Haskell functions that mimic deriving extensions that were introduced or modified in recent versions of GHC. Currently, the following extensions are covered:

* `DeriveFoldable`
* `DeriveFunctor`
* `DeriveTraversable`

The following changes have been backported:

* In GHC 8.0, `DeriveFoldable` was changed to allow folding over data types with existential constraints.
* In GHC 8.0, `DeriveFoldable` and `DeriveTraversable` were changed so as not to generate superfluous `mempty` or `pure` expressions in generated code. As a result, this allows deriving `Traversable` instances for datatypes with unlifted argument types.

Note that some recent GHC extensions are not covered by this package:

* `DeriveGeneric`, which was introducted in GHC 7.2 for deriving `Generic` instances, and modified in GHC 7.6 to allow derivation of `Generic1` instances. Use `Generics.Deriving.TH` from [`generic-deriving`](http://hackage.haskell.org/package/generic-deriving) to derive `Generic(1)` using Template Haskell.
* `DeriveLift`, which was introduced in GHC 8.0 for deriving `Lift` instances. Use `Language.Haskell.TH.Lift` from [`th-lift`](http://hackage.haskell.org/package/th-lift) to derive `Lift` using Template Haskell.