Generic.Data

Generic (<>) (or mappend).

instance Semigroup MyType where
  (<>) = gmappend

See also gmempty.

Generic mempty.

instance Monoid MyType where
  mempty = gmempty

Generic (<>) (or mappend).

The difference from gmappend is the Monoid constraint instead of Semigroup, for older versions of base where Semigroup is not a superclass of Monoid.

Generic (==).

instance Eq MyType where
  (==) = geq

Generic compare.

instance Ord MyType where
  compare = gcompare

Generic readPrec.

instance Read MyType where
  readPrec = Text.Read.greadPrec
  readListPrec = readListPrecDefault

Generic representation of Read types.

Generic showsPrec.

instance Show MyType where
  showsPrec = gshowsPrec

Generic representation of Show types.

Generic representation of Enum types.

The opts parameter is a type-level option to select different implementations.

Standard option for GEnum: derive Enum for types with only nullary constructors (the same restrictions as in the Haskell 2010 report).

Generic toEnum generated with the StandardEnum option.

instance Enum MyType where
  toEnum = gtoEnum
  fromEnum = gfromEnum
  enumFrom = genumFrom
  enumFromThen = genumFromThen
  enumFromTo = genumFromTo
  enumFromThenTo = genumFromThenTo

Generic fromEnum generated with the StandardEnum option.

See also gtoEnum.

Generic enumFrom generated with the StandardEnum option.

See also gtoEnum.

Generic enumFromThen generated with the StandardEnum option.

See also gtoEnum.

Generic enumFromTo generated with the StandardEnum option.

See also gtoEnum.

Generic enumFromThenTo generated with the StandardEnum option.

See also gtoEnum.

Extends the StandardEnum option for GEnum to allow all constructors to have arbitrary many fields. Each field type must be an instance of both Enum and Bounded. Avoid fields of types Int and Word.

Details

Two restrictions require the user's attention:

• The Enum instances of the field types need to start enumerating from 0. In particular, Int is an unfit field type, because the enumeration of the negative values starts before 0.

• There can only be up to maxBound :: Int values (because the implementation represents the cardinality explicitly as an Int). This restriction makes Word an invalid field type as well. Notably, it is insufficient for each individual field types to stay below this limit. Instead it applies to the generic type as a whole.

Elements are numbered by toEnum, from 0 up to (cardinality - 1). The resulting ordering matches the generic Ord instance defined by Generic.Data.gcompare. The values from different constructors are enumerated sequentially.

data Example = C0 Bool Bool | C1 Bool
  deriving (Eq, Ord, Show, Generic)

cardinality = 6  -- 2    * 2    + 2
                 -- Bool * Bool | Bool

enumeration =
    [ C0 False False
    , C0 False  True
    , C0  True False
    , C0  True  True
    , C1 False
    , C1 True
    ]

enumeration == map gtoFiniteEnum [0 .. 5]
[0 .. 5] == map gfromFiniteEnum enumeration

Generic toEnum generated with the FiniteEnum option.

instance Enum MyType where
  toEnum = gtoFiniteEnum
  fromEnum = gfromFiniteEnum
  enumFrom = gfiniteEnumFrom
  enumFromThen = gfiniteEnumFromThen
  enumFromTo = gfiniteEnumFromTo
  enumFromThenTo = gfiniteEnumFromThenTo

Generic fromEnum generated with the FiniteEnum option.

See also gtoFiniteEnum.

Generic enumFrom generated with the FiniteEnum option.

See also gtoFiniteEnum.

Generic enumFromThen generated with the FiniteEnum option.

See also gtoFiniteEnum.

Generic enumFromTo generated with the FiniteEnum option.

See also gtoFiniteEnum.

Generic enumFromThenTo generated with the FiniteEnum option.

See also gtoFiniteEnum.

Generic minBound.

instance Bounded MyType where
  minBound = gminBound
  maxBound = gmaxBound

Generic maxBound.

See also gminBound.

Generic representation of Bounded types.

Generic range.

import Data.Ix
instance Ix MyType where
  range = grange
  index = gindex
  inRange = ginRange

Generic index.

See also grange.

Generic inRange.

See also grange.

Generic representation of Ix types.

Generic unsafeIndex.

Details

The functions unsafeIndex and unsafeRangeSize belong to Ix but are internal to GHC and hence not exported from the module Data.Ix. However they are exported from the module GHC.Arr. See grange for how to define an instance of Ix such that it does not depend on the stability of GHCs internal API. Unfortunately this results in additional (unnecessary) bound checks. With the danger of having no stability guarantees for GHC's internal API one can alternatively define an instance of Ix as

import GHC.Arr
instance Ix MyType where
  range = grange
  unsafeIndex = gunsafeIndex
  inRange = ginRange

Generic fmap.

instance Functor MyTypeF where
  fmap = gfmap

Generic (<$).

See also gfmap.

Generic foldMap.

instance Foldable MyTypeF where
  foldMap = gfoldMap

Generic foldr.

instance Foldable MyTypeF where
  foldr = gfoldr

See also gfoldMap.

Class of generic representations for which Foldable can be derived.

Generic traverse.

instance Traversable MyTypeF where
  traverse = gtraverse

Generic sequenceA.

instance Traversable MyTypeF where
  sequenceA = gsequenceA

See also gtraverse.

Class of generic representations for which Traversable can be derived.

Generic pure.

instance Applicative MyTypeF where
  pure = gpure
  (<*>) = gap

Generic (<*>) (or ap).

See also gpure.

Generic liftA2.

See also gpure.

Generic empty.

instance Alternative MyTypeF where
  empty = gempty
  (<|>) = galt

Generic (<|>).

See also gempty.

Generic liftEq.

Generic liftCompare.

Generic liftReadPrec.

Generic representation of Read1 types.

Generic liftShowsPrec.

Generic representation of Show1 types.

Name of the first data constructor in a type as a string.

>>> gdatatypeName @(Maybe Int)"Maybe"

Name of the module where the first type constructor is defined.

>>> gmoduleName @(ZipList Int)"Control.Applicative"

Name of the package where the first type constructor is defined.

>>> gpackageName @(Maybe Int)"base"

True if the first type constructor is a newtype.

>>> gisNewtype @[Int]False>>> gisNewtype @(ZipList Int)True

Generic representations that contain datatype metadata.

Name of the first constructor in a value.

>>> gconName (Just 0)"Just"

The fixity of the first constructor.

>>> import GHC.Generics ((:*:)(..))>>> gconFixity (Just 0)Prefix>>> gconFixity ([] :*: id)Infix RightAssociative 6

True if the constructor is a record.

>>> gconIsRecord (Just 0)False>>> gconIsRecord (Sum 0)   -- Note:  newtype Sum a = Sum { getSum :: a }True

Number of constructors.

>>> gconNum @(Maybe Int)2

Index of a constructor.

>>> gconIndex Nothing0>>> gconIndex (Just "test")1

Constraint synonym for Generic and GConstructors.

Generic representations that contain constructor metadata.

An opaque identifier for a constructor.

Identifier of a constructor.

Index of a constructor, given its identifier. See also gconIndex.

Name of a constructor. See also gconName.

All constructor identifiers.

gconNum @a = length (conIdEnum @a)

Get a ConId by name.

>>> conIdNamed @"Nothing" :: ConId (Maybe Int)ConId 0>>> conIdNamed @"Just"    :: ConId (Maybe Int)ConId 1

Constraint synonym for generic types a with a constructor named n.

The first constructor. This must not be called on an empty type.

The last constructor. This must not be called on an empty type.

Constraint that a generic type a is not empty. Producing an error message otherwise.

The Symbol parameter fname is used only for error messages.

It is implied by the simpler constraint IsEmptyType a ~ 'False

True if the generic type a is empty.

Meta field of the M1 type constructor.

Name of the data type (MetaData).

Name of the module where the data type is defined (MetaData)

Name of the package where the data type is defined (MetaData)

True if the data type is a newtype (MetaData).

Name of the constructor (MetaCons).

Fixity of the constructor (MetaCons).

True for a record constructor (MetaCons).

Just the name of the record field, if it is one (MetaSel).

Name of the record field; undefined for non-record fields (MetaSel).

Unpackedness annotation of a field (MetaSel).

Strictness annotation of a field (MetaSel).

Inferred strictness of a field (MetaSel).