generic-data-0.6.0.1: Deriving instances with GHC.Generics and related utilities

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LanguageHaskell2010

Generic.Data.Microsurgery

Contents

Description

Simple operations on generic representations, that only change the type-level metadata used by certain generic functions.

More complex ones can be found in generic-data-surgery but also, perhaps surprisingly, in generic-lens (read more about this just below) and one-liner.

Synopsis

Surgeries with generic-lens

One common and simple situation is to modify the type of some fields, for example wrapping them in a newtype.

We can leverage the generic-lens library, with the two functions below.

-- Lens to a field named fd in a Generic record.
field_ :: HasField_ fd s t a b => Lens s t a b  -- from generic-lens

-- Update a value through a lens (ASetter is a specialization of Lens).
over :: ASetter s t a b -> (a -> b) -> s -> t   -- from lens or microlens

For example, here is a record type:

data R = R { myField :: Int } deriving Generic

The function over (field_ @"myField") Opaque applies the newtype constructor Opaque to the field "myField", but this actually doesn't typecheck as-is. With a bit of help from this module, we can wrap that function as follows:

onData (over (field_ @"myField") Opaque) . toData
  :: R -> Data _ _   -- type arguments hidden

The result has a type Data _ _, that from the point of view of GHC.Generics looks just like R but with the field "myField" wrapped in Opaque, as if we had defined:

data R = R { myField :: Opaque Int } deriving Generic

Example usage

We derive an instance of Show that hides the "myField" field, whatever its type.

instance Show R where
  showsPrec n = gshowsPrec n
    . onData (over (field_ @"myField") Opaque)
    . toData

show (R 3) = "R {myField = _}"

Deriving via

type Surgery (s :: *) (a :: *) = Generically (Surgery' s a) Source #

Apply a microsurgery s to a type a for DerivingVia.

Example

Expand
{-# LANGUAGE DerivingVia #-}

-- The constructors must be visible.
import Generic.Data.Microsurgery
  (Surgery, Surgery'(..), Generically(..), Derecordify)

data T = T { unT :: Int }
  deriving Show via (Surgery Derecordify T)

-- T won't be shown as a record:
--   show (T {unT = 3}) == "T 3"

newtype Surgery' (s :: *) (a :: *) Source #

Constructors

Surgery' 

Fields

Instances
(Generic a, Coercible (GSurgery s (Rep a)) (Rep a)) => Generic (Surgery' s a) Source # 
Instance details

Defined in Generic.Data.Internal.Microsurgery

Associated Types

type Rep (Surgery' s a) :: Type -> Type #

Methods

from :: Surgery' s a -> Rep (Surgery' s a) x #

to :: Rep (Surgery' s a) x -> Surgery' s a #

type Rep (Surgery' s a) Source # 
Instance details

Defined in Generic.Data.Internal.Microsurgery

type Rep (Surgery' s a) = GSurgery s (Rep a)

type family GSurgery (s :: *) (f :: k -> *) :: k -> * Source #

Apply a microsurgery represented by a symbol s (declared as a dummy data type) to a generic representation f.

Instances
type GSurgery Derecordify (f :: k -> Type) Source # 
Instance details

Defined in Generic.Data.Internal.Microsurgery

type GSurgery Derecordify (f :: k -> Type) = GDerecordify f
type GSurgery Typeage (M1 D (MetaData nm md pk _nt) f :: k -> Type) Source # 
Instance details

Defined in Generic.Data.Internal.Microsurgery

type GSurgery Typeage (M1 D (MetaData nm md pk _nt) f :: k -> Type) = M1 D (MetaData nm md pk False) f
type GSurgery (RenameFields rnm) (f :: k -> Type) Source # 
Instance details

Defined in Generic.Data.Internal.Microsurgery

type GSurgery (RenameFields rnm) (f :: k -> Type) = GRenameFields rnm f
type GSurgery (RenameConstrs rnm) (f :: k -> Type) Source # 
Instance details

Defined in Generic.Data.Internal.Microsurgery

type GSurgery (RenameConstrs rnm) (f :: k -> Type) = GRenameConstrs rnm f
type GSurgery (OnFields f) (g :: k -> Type) Source # 
Instance details

Defined in Generic.Data.Internal.Microsurgery

type GSurgery (OnFields f) (g :: k -> Type) = GOnFields f g

newtype Generically a Source #

Type with instances derived via Generic.

Constructors

Generically 

Fields

Instances
(Generic a, GBounded (Rep a)) => Bounded (Generically a) Source # 
Instance details

Defined in Generic.Data.Internal.Generically

(Generic a, GEnum StandardEnum (Rep a)) => Enum (Generically a) Source # 
Instance details

Defined in Generic.Data.Internal.Generically

(Generic a, Eq (Rep a ())) => Eq (Generically a) Source # 
Instance details

Defined in Generic.Data.Internal.Generically

(Generic a, Ord (Rep a ())) => Ord (Generically a) Source # 
Instance details

Defined in Generic.Data.Internal.Generically

(Generic a, GShow0 (Rep a)) => Show (Generically a) Source # 
Instance details

Defined in Generic.Data.Internal.Generically

Generic a => Generic (Generically a) Source # 
Instance details

Defined in Generic.Data.Internal.Generically

Associated Types

type Rep (Generically a) :: Type -> Type #

Methods

from :: Generically a -> Rep (Generically a) x #

to :: Rep (Generically a) x -> Generically a #

(Generic a, Semigroup (Rep a ())) => Semigroup (Generically a) Source # 
Instance details

Defined in Generic.Data.Internal.Generically

(Generic a, Monoid (Rep a ())) => Monoid (Generically a) Source # 
Instance details

Defined in Generic.Data.Internal.Generically

type Rep (Generically a) Source # 
Instance details

Defined in Generic.Data.Internal.Generically

type Rep (Generically a) = Rep a

Synthetic types

data Data r p Source #

Synthetic data type.

A wrapper to view a generic Rep as the datatype it's supposed to represent, without needing a declaration.

Instances
Monad r => Monad (Data r) Source # 
Instance details

Defined in Generic.Data.Internal.Data

Methods

(>>=) :: Data r a -> (a -> Data r b) -> Data r b #

(>>) :: Data r a -> Data r b -> Data r b #

return :: a -> Data r a #

fail :: String -> Data r a #

Functor r => Functor (Data r) Source # 
Instance details

Defined in Generic.Data.Internal.Data

Methods

fmap :: (a -> b) -> Data r a -> Data r b #

(<$) :: a -> Data r b -> Data r a #

Applicative r => Applicative (Data r) Source # 
Instance details

Defined in Generic.Data.Internal.Data

Methods

pure :: a -> Data r a #

(<*>) :: Data r (a -> b) -> Data r a -> Data r b #

liftA2 :: (a -> b -> c) -> Data r a -> Data r b -> Data r c #

(*>) :: Data r a -> Data r b -> Data r b #

(<*) :: Data r a -> Data r b -> Data r a #

Foldable r => Foldable (Data r) Source # 
Instance details

Defined in Generic.Data.Internal.Data

Methods

fold :: Monoid m => Data r m -> m #

foldMap :: Monoid m => (a -> m) -> Data r a -> m #

foldr :: (a -> b -> b) -> b -> Data r a -> b #

foldr' :: (a -> b -> b) -> b -> Data r a -> b #

foldl :: (b -> a -> b) -> b -> Data r a -> b #

foldl' :: (b -> a -> b) -> b -> Data r a -> b #

foldr1 :: (a -> a -> a) -> Data r a -> a #

foldl1 :: (a -> a -> a) -> Data r a -> a #

toList :: Data r a -> [a] #

null :: Data r a -> Bool #

length :: Data r a -> Int #

elem :: Eq a => a -> Data r a -> Bool #

maximum :: Ord a => Data r a -> a #

minimum :: Ord a => Data r a -> a #

sum :: Num a => Data r a -> a #

product :: Num a => Data r a -> a #

Traversable r => Traversable (Data r) Source # 
Instance details

Defined in Generic.Data.Internal.Data

Methods

traverse :: Applicative f => (a -> f b) -> Data r a -> f (Data r b) #

sequenceA :: Applicative f => Data r (f a) -> f (Data r a) #

mapM :: Monad m => (a -> m b) -> Data r a -> m (Data r b) #

sequence :: Monad m => Data r (m a) -> m (Data r a) #

Contravariant r => Contravariant (Data r) Source # 
Instance details

Defined in Generic.Data.Internal.Data

Methods

contramap :: (a -> b) -> Data r b -> Data r a #

(>$) :: b -> Data r b -> Data r a #

Eq1 r => Eq1 (Data r) Source # 
Instance details

Defined in Generic.Data.Internal.Data

Methods

liftEq :: (a -> b -> Bool) -> Data r a -> Data r b -> Bool #

Ord1 r => Ord1 (Data r) Source # 
Instance details

Defined in Generic.Data.Internal.Data

Methods

liftCompare :: (a -> b -> Ordering) -> Data r a -> Data r b -> Ordering #

GShow1 r => Show1 (Data r) Source # 
Instance details

Defined in Generic.Data.Internal.Data

Methods

liftShowsPrec :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> Int -> Data r a -> ShowS #

liftShowList :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> [Data r a] -> ShowS #

Alternative r => Alternative (Data r) Source # 
Instance details

Defined in Generic.Data.Internal.Data

Methods

empty :: Data r a #

(<|>) :: Data r a -> Data r a -> Data r a #

some :: Data r a -> Data r [a] #

many :: Data r a -> Data r [a] #

MonadPlus r => MonadPlus (Data r) Source # 
Instance details

Defined in Generic.Data.Internal.Data

Methods

mzero :: Data r a #

mplus :: Data r a -> Data r a -> Data r a #

Generic1 (Data r :: Type -> Type) Source # 
Instance details

Defined in Generic.Data.Internal.Data

Associated Types

type Rep1 (Data r) :: k -> Type #

Methods

from1 :: Data r a -> Rep1 (Data r) a #

to1 :: Rep1 (Data r) a -> Data r a #

GBounded r => Bounded (Data r p) Source # 
Instance details

Defined in Generic.Data.Internal.Data

Methods

minBound :: Data r p #

maxBound :: Data r p #

GEnum StandardEnum r => Enum (Data r p) Source # 
Instance details

Defined in Generic.Data.Internal.Data

Methods

succ :: Data r p -> Data r p #

pred :: Data r p -> Data r p #

toEnum :: Int -> Data r p #

fromEnum :: Data r p -> Int #

enumFrom :: Data r p -> [Data r p] #

enumFromThen :: Data r p -> Data r p -> [Data r p] #

enumFromTo :: Data r p -> Data r p -> [Data r p] #

enumFromThenTo :: Data r p -> Data r p -> Data r p -> [Data r p] #

Eq (r p) => Eq (Data r p) Source # 
Instance details

Defined in Generic.Data.Internal.Data

Methods

(==) :: Data r p -> Data r p -> Bool #

(/=) :: Data r p -> Data r p -> Bool #

Ord (r p) => Ord (Data r p) Source # 
Instance details

Defined in Generic.Data.Internal.Data

Methods

compare :: Data r p -> Data r p -> Ordering #

(<) :: Data r p -> Data r p -> Bool #

(<=) :: Data r p -> Data r p -> Bool #

(>) :: Data r p -> Data r p -> Bool #

(>=) :: Data r p -> Data r p -> Bool #

max :: Data r p -> Data r p -> Data r p #

min :: Data r p -> Data r p -> Data r p #

(GShow1 r, Show p) => Show (Data r p) Source # 
Instance details

Defined in Generic.Data.Internal.Data

Methods

showsPrec :: Int -> Data r p -> ShowS #

show :: Data r p -> String #

showList :: [Data r p] -> ShowS #

(Functor r, Contravariant r) => Generic (Data r p) Source # 
Instance details

Defined in Generic.Data.Internal.Data

Associated Types

type Rep (Data r p) :: Type -> Type #

Methods

from :: Data r p -> Rep (Data r p) x #

to :: Rep (Data r p) x -> Data r p #

Semigroup (r p) => Semigroup (Data r p) Source # 
Instance details

Defined in Generic.Data.Internal.Data

Methods

(<>) :: Data r p -> Data r p -> Data r p #

sconcat :: NonEmpty (Data r p) -> Data r p #

stimes :: Integral b => b -> Data r p -> Data r p #

Monoid (r p) => Monoid (Data r p) Source # 
Instance details

Defined in Generic.Data.Internal.Data

Methods

mempty :: Data r p #

mappend :: Data r p -> Data r p -> Data r p #

mconcat :: [Data r p] -> Data r p #

type Rep1 (Data r :: Type -> Type) Source # 
Instance details

Defined in Generic.Data.Internal.Data

type Rep1 (Data r :: Type -> Type) = r
type Rep (Data r p) Source # 
Instance details

Defined in Generic.Data.Internal.Data

type Rep (Data r p) = r

toData :: Generic a => a -> Data (Rep a) p Source #

Conversion between a generic type and the synthetic type made using its representation.

fromData :: Generic a => Data (Rep a) p -> a Source #

Inverse of fromData.

onData :: (UnifyRep r s, UnifyRep s r) => p (Data r x) (Data s y) -> p (Data r x) (Data s y) Source #

onData :: _ => (Data r x -> Data s y) -> (Data r x -> Data s y)  -- possible specialization

Can be used with generic-lens for type-changing field updates with field_ (and possibly other generic optics).

A specialization of the identity function to be used to fix types of functions on Data, unifying the "spines" of input and output generic representations (the "spine" is everything except field types, which may thus change).

Microsurgeries

Each microsurgery consists of a type family F to modify metadata in GHC Generic representations, and two mappings (that are just coerce):

  f :: Data (Rep a) p -> Data (F (Rep a)) p
unf :: Data (F (Rep a)) p -> Data (Rep a) p

Use f with toData for generic functions that consume generic values, and unf with fromData for generic functions that produce generic values. Abstract example:

genericSerialize . f . toData
fromData . unf . genericDeserialize

Derecordify

data Derecordify :: * Source #

Forget that a type was declared using record syntax.

data Foo = Bar { baz :: Zap }

-- becomes --

data Foo = Bar Zap

Concretely, set the last field of MetaCons to False and forget field names.

This is a defunctionalized symbol, to be applied using GSurgery.

Instances
type GSurgery Derecordify (f :: k -> Type) Source # 
Instance details

Defined in Generic.Data.Internal.Microsurgery

type GSurgery Derecordify (f :: k -> Type) = GDerecordify f

Type aging ("denewtypify")

data Typeage :: * Source #

Forget that a type is a newtype. (The pun is that "aging" a type makes it no longer "new".)

newtype Foo = Bar Baz

-- becomes --

data Foo = Bar Baz

This is a defunctionalized symbol, to be applied using GSurgery.

Instances
type GSurgery Typeage (M1 D (MetaData nm md pk _nt) f :: k -> Type) Source # 
Instance details

Defined in Generic.Data.Internal.Microsurgery

type GSurgery Typeage (M1 D (MetaData nm md pk _nt) f :: k -> Type) = M1 D (MetaData nm md pk False) f

Renaming of fields and constructors

These surgeries require DataKinds and TypeApplications.

Examples

{-# LANGUAGE
    DataKinds,
    TypeApplications #-}

-- Rename all fields to "foo"
renameFields @(SConst "foo")

-- Rename constructor "Bar" to "Baz", and leave all others the same
renameConstrs @(SRename '[ '("Bar", "Baz") ] SId)

data RenameFields (rnm :: *) :: * Source #

Rename fields using the function rnm given as a parameter.

data Foo = Bar { baz :: Zap }

-- becomes, renaming "baz" to "bag" --

data Foo = Bar { bag :: Zap }

This is a defunctionalized symbol, to be applied using GSurgery.

Instances
type GSurgery (RenameFields rnm) (f :: k -> Type) Source # 
Instance details

Defined in Generic.Data.Internal.Microsurgery

type GSurgery (RenameFields rnm) (f :: k -> Type) = GRenameFields rnm f

renameFields :: forall rnm f p. Coercible (GSurgery (RenameFields rnm) f) f => Data f p -> Data (GSurgery (RenameFields rnm) f) p Source #

unrenameFields :: forall rnm f p. Coercible (GSurgery (RenameFields rnm) f) f => Data f p -> Data (GSurgery (RenameFields rnm) f) p Source #

data RenameConstrs (rnm :: *) :: * Source #

Rename constructors using the function rnm given as a parameter.

data Foo = Bar { baz :: Zap }

-- becomes, renaming "Bar" to "Car" --

data Foo = Car { baz :: Zap }

This is a defunctionalized symbol, to be applied using GSurgery.

Instances
type GSurgery (RenameConstrs rnm) (f :: k -> Type) Source # 
Instance details

Defined in Generic.Data.Internal.Microsurgery

type GSurgery (RenameConstrs rnm) (f :: k -> Type) = GRenameConstrs rnm f

renameConstrs :: forall rnm f p. Coercible (GSurgery (RenameConstrs rnm) f) f => Data f p -> Data (GSurgery (RenameConstrs rnm) f) p Source #

unrenameConstrs :: forall rnm f p. Coercible (GSurgery (RenameConstrs rnm) f) f => Data f p -> Data (GSurgery (RenameConstrs rnm) f) p Source #

Renaming functions

type family (f :: *) @@ (s :: Symbol) :: Symbol Source #

f @@ s is the application of a type-level function symbolized by f to a s :: Symbol.

A function FooToBar can be defined as follows:

data FooToBar
type instance FooToBar @@ "foo" = "bar"
Instances
type SError @@ s Source # 
Instance details

Defined in Generic.Data.Internal.Microsurgery

type SError @@ s = (TypeError (Text "Invalid name: " :<>: ShowType s) :: Symbol)
type SId @@ s Source # 
Instance details

Defined in Generic.Data.Internal.Microsurgery

type SId @@ s = s
type (SConst z) @@ _s Source # 
Instance details

Defined in Generic.Data.Internal.Microsurgery

type (SConst z) @@ _s = z
type (SRename xs f) @@ s Source # 
Instance details

Defined in Generic.Data.Internal.Microsurgery

type (SRename xs f) @@ s = SRename' xs f s

data SId Source #

Identity function Symbol -> Symbol.

Instances
type SId @@ s Source # 
Instance details

Defined in Generic.Data.Internal.Microsurgery

type SId @@ s = s

data SError Source #

Empty function (compile-time error when applied).

Instances
type SError @@ s Source # 
Instance details

Defined in Generic.Data.Internal.Microsurgery

type SError @@ s = (TypeError (Text "Invalid name: " :<>: ShowType s) :: Symbol)

data SConst (s :: Symbol) Source #

Constant function.

Instances
type (SConst z) @@ _s Source # 
Instance details

Defined in Generic.Data.Internal.Microsurgery

type (SConst z) @@ _s = z

data SRename (xs :: [(Symbol, Symbol)]) (f :: *) Source #

Define a function for a fixed set of strings, and fall back to f for the others.

Instances
type (SRename xs f) @@ s Source # 
Instance details

Defined in Generic.Data.Internal.Microsurgery

type (SRename xs f) @@ s = SRename' xs f s

Wrap every field in a type constructor

Give every field a type f FieldType (where f is a parameter), to obtain a family of types with a shared structure. This "higher-kindification" technique is presented in the following blogposts:

See also the file test/one-liner-surgery.hs in this package for an example of using one-liner and generic-lens with a synthetic type constructed with DOnFields.

data OnFields (f :: * -> *) :: * Source #

Apply a type constructor f to every field type of a generic representation r.

This is a defunctionalized symbol, to be applied using GSurgery.

Instances
type GSurgery (OnFields f) (g :: k -> Type) Source # 
Instance details

Defined in Generic.Data.Internal.Microsurgery

type GSurgery (OnFields f) (g :: k -> Type) = GOnFields f g

type DOnFields (f :: * -> *) (a :: *) = Data (GSurgery (OnFields f) (Rep a)) () Source #

Apply a type constructor to every field type of a type a to make a synthetic type.