# deriving-compat

Backports of GHC deriving extensions https://github.com/haskell-compat/deriving-compat

Version on this page: | 0.3.6 |

LTS Haskell 11.14: | 0.4.3 |

Stackage Nightly 2018-06-17: | 0.4.3 |

Latest on Hackage: | 0.4.3 |

**Ryan Scott**

**Ryan Scott**

#### Module documentation for 0.3.6

- Data
- Data.Bounded
- Data.Deriving
- Data.Enum
- Data.Eq
- Data.Foldable
- Data.Functor
- Data.Ix
- Data.Ord
- Data.Traversable

- Text
- Text.Read
- Text.Show

`deriving-compat`

[][Haskell.org] [][tl;dr Legal: BSD3]

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 typeclasses/extensions are covered:

- Deriving
`Bounded`

- Deriving
`Enum`

- Deriving
`Ix`

- Deriving
`Eq`

,`Eq1`

, and`Eq2`

- Deriving
`Ord`

,`Ord1`

, and`Ord2`

- Deriving
`Read`

,`Read1`

, and`Read2`

- Deriving
`Show`

,`Show1`

, and`Show2`

`DeriveFoldable`

`DeriveFunctor`

`DeriveTraversable`

`GeneralizedNewtypeDeriving`

(with GHC 8.2 or later)`DerivingVia`

(with GHC 8.2 or later)

See the `Data.Deriving`

module for a full list of backported changes.

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

`DeriveDataTypeable`

`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`

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`

to derive`Lift`

using Template Haskell.- The
`Bifunctor`

typeclass, which was introduced in GHC 7.10, as well as the`Bifoldable`

and`Bitraversable`

typeclasses, which were introduced in GHC 8.2. Use`Data.Bifunctor.TH`

from`bifunctors`

to derive these typeclasses using Template Haskell.

## Changes

### 0.4.3 [2018.06.16]

Fix a bug that caused debug-enabled GHC builds to panic when generating code from this library (see Trac #15270). The fix only affects the library's internals, so no changes are user-facing.

### 0.4.2 [2018.05.14]

Backport the fixes for GHC Trac #14364 and #14918, which significantly improve the compliation times of derived

`Read`

instances.

### 0.4.1 [2018.02.04]

- Add
`Data.Deriving.Via`

, which allows emulating the behavior of the`GeneralizedNewtypeDeriving`

and`DerivingVia`

extensions. - Test suite fixes for GHC 8.4.

## 0.4 [2017.12.07]

- Incorporate changes from the
`EmptyDataDeriving`

proposal (which is in GHC as of 8.4):*For derived*For derived`Eq`

and`Ord`

instances for empty data types, simply return`True`

and`EQ`

, respectively, without inspecting the arguments.`Read`

instances for empty data types, simply return`pfail`

(without`parens`

).*For derived*For derived`Show`

instances for empty data types, inspect the argument (instead of`error`

ing). In addition, add`showEmptyCaseBehavior`

to`ShowOptions`

, which configures whether derived instances for empty data types should use the`EmptyCase`

extension (this is disabled by default).`Functor`

and`Traversable`

instances for empty data types, make`fmap`

and`traverse`

strict in its argument.*For derived*Add`Foldable`

instances, do not error on empty data types. Instead, simply return the folded state (for`foldr`

) or`mempty`

(for`foldMap`

), without inspecting the arguments.`FFTOptions`

(`Functor`

/`Foldable`

/`Traversable`

options) to`Data.Functor.Deriving`

, along with variants of existing functions that take`FFTOptions`

as an argument. For now, the only configurable option is whether derived instances for empty data types should use the`EmptyCase`

extension (this is disabled by default). - Backport the fix to #13328. That is, when deriving
`Functor`

or`Traversable`

instances for data types where the last type variable is at phantom role, generated`fmap`

/`traverse`

implementations now use`coerce`

for efficiency. - Rename
`emptyCaseBehavior`

from`Data.Functor.Deriving`

to`fftEmptyCaseBehavior`

.

### 0.3.6 [2017.04.10]

- Make
`deriveTraversable`

use`liftA2`

in derived implementations of`traverse`

when possible, now that`liftA2`

is a class method of`Applicative`

(as of GHC 8.2) - Make
`deriveShow`

use`showCommaSpace`

, a change introduced in GHC 8.2

### 0.3.5 [2016.12.12]

Fix bug in which derived

`Ord`

instances for datatypes with many constructors would fail to typecheck

### 0.3.4 [2016.10.20]

- Fix bug in which infix record selectors weren't shown with parentheses in derived
`Show`

instances - Fix bug in which record selectors weren't parsed correctly in derived
`Read`

instances

### 0.3.3 [2016.09.11]

- Add
`Data.Bounded.Deriving`

, which allows deriving`Bounded`

with TH. - Add
`Data.Enum.Deriving`

, which allows deriving`Enum`

with TH. - Add
`Data.Ix.Deriving`

, which allows deriving`Ix`

with TH. - Fix bug in which derived
`Show`

instance would parenthesize the output too eagerly

### 0.3.2

- Incorporate a fix to GHC Trac #10858, which will be introduced in GHC 8.2
- Fix bug in which derived
`Ord`

instances accidentally swapped their less-than(-or-equal-to) and greater-than(-or-equal-to) methods - Fix GHC HEAD build

### 0.3.1

- Allow deriving
`Functor`

and`Foldable`

instances for datatypes containing unboxed tuples - Microoptimization in derived instances of higher-order versions of
`Eq`

,`Ord`

,`Read`

, and`Show`

## 0.3

- Added
`Data.Eq.Deriving`

, which allows deriving`Eq`

,`Eq1`

, and`Eq2`

with TH. - Added
`Data.Ord.Deriving`

, which allows deriving`Ord`

,`Ord1`

, and`Ord2`

with TH. - Added
`Data.Read.Deriving`

, which allows deriving`Read`

,`Read1`

, and`Eq2`

with TH. - Renamed
`Text.Show.Deriving.Options`

to`ShowOptions`

so as to disambiguate it from the options datatypes in other`deriving-compat`

modules.

### 0.2.2

Fixed a bug in

`Text.Show.Deriving`

's treatment of unlifted types

### 0.2.1

Added

`Text.Show.Deriving`

, which allows deriving`Show`

,`Show1`

, and`Show2`

with TH.

## 0.2

- Added support for GHC 8.0
- Added
`Data.Functor.Deriving`

and`Data.Traversable.Deriving`

, which allow deriving`Functor`

and`Traversable`

with TH. - Added
`Data.Deriving`

, which reexports all other modules

## 0.1

- Initial commit