Copyright	(C) 2015-2017 Ryan Scott
License	BSD-style (see the file LICENSE)
Maintainer	Ryan Scott
Portability	Template Haskell
Safe Haskell	None
Language	Haskell2010

Data.Traversable.Deriving

Contents

Traversable
FFTOptions
deriveTraversable limitations

Description

Exports functions to mechanically derive Traversable instances in a way that mimics how the -XDeriveTraversable extension works since GHC 8.0.

Derived Traversable instances from this module do not generate superfluous pure expressions in its implementation of traverse. One can verify this by compiling a module that uses deriveTraversable with the -ddump-splices GHC flag.

These changes make it possible to derive Traversable instances for data types with unlifted argument types, e.g.,

data IntHash a = IntHash Int# a

deriving instance Traversable IntHash -- On GHC 8.0  on later
$(deriveTraversable ''IntHash)        -- On GHC 7.10 and earlier

For more info on these changes, see this GHC wiki page.

Synopsis

deriveTraversable :: Name -> Q [Dec]
deriveTraversableOptions :: FFTOptions -> Name -> Q [Dec]
makeTraverse :: Name -> Q Exp
makeTraverseOptions :: FFTOptions -> Name -> Q Exp
makeSequenceA :: Name -> Q Exp
makeSequenceAOptions :: FFTOptions -> Name -> Q Exp
makeMapM :: Name -> Q Exp
makeMapMOptions :: FFTOptions -> Name -> Q Exp
makeSequence :: Name -> Q Exp
makeSequenceOptions :: FFTOptions -> Name -> Q Exp
newtype FFTOptions = FFTOptions {
- fftEmptyCaseBehavior :: Bool
}
defaultFFTOptions :: FFTOptions

`Traversable`

deriveTraversable :: Name -> Q [Dec] Source #

Generates a Traversable instance declaration for the given data type or data family instance.

deriveTraversableOptions :: FFTOptions -> Name -> Q [Dec] Source #

Like deriveTraverse, but takes an FFTOptions argument.

makeTraverse :: Name -> Q Exp Source #

Generates a lambda expression which behaves like traverse (without requiring a Traversable instance).

makeTraverseOptions :: FFTOptions -> Name -> Q Exp Source #

Like makeTraverse, but takes an FFTOptions argument.

makeSequenceA :: Name -> Q Exp Source #

Generates a lambda expression which behaves like sequenceA (without requiring a Traversable instance).

makeSequenceAOptions :: FFTOptions -> Name -> Q Exp Source #

Like makeSequenceA, but takes an FFTOptions argument.

makeMapM :: Name -> Q Exp Source #

Generates a lambda expression which behaves like mapM (without requiring a Traversable instance).

makeMapMOptions :: FFTOptions -> Name -> Q Exp Source #

Like makeMapM, but takes an FFTOptions argument.

makeSequence :: Name -> Q Exp Source #

Generates a lambda expression which behaves like sequence (without requiring a Traversable instance).

makeSequenceOptions :: FFTOptions -> Name -> Q Exp Source #

Like makeSequence, but takes an FFTOptions argument.

`FFTOptions`

newtype FFTOptions Source #

Options that further configure how the functions in Data.Functor.Deriving should behave. (FFT stands for 'Functor'/'Foldable'/'Traversable'.)

Constructors

FFTOptions
Fields fftEmptyCaseBehavior :: Bool If `True`, derived instances for empty data types (i.e., ones with no data constructors) will use the `EmptyCase` language extension. If `False`, derived instances will simply use `seq` instead. (This has no effect on GHCs before 7.8, since `EmptyCase` is only available in 7.8 or later.)

Instances

Eq FFTOptions Source #
Instance details Defined in Data.Functor.Deriving.Internal Methods (==) :: FFTOptions -> FFTOptions -> Bool # (/=) :: FFTOptions -> FFTOptions -> Bool #
Ord FFTOptions Source #
Instance details Defined in Data.Functor.Deriving.Internal Methods compare :: FFTOptions -> FFTOptions -> Ordering # (<) :: FFTOptions -> FFTOptions -> Bool # (<=) :: FFTOptions -> FFTOptions -> Bool # (>) :: FFTOptions -> FFTOptions -> Bool # (>=) :: FFTOptions -> FFTOptions -> Bool # max :: FFTOptions -> FFTOptions -> FFTOptions # min :: FFTOptions -> FFTOptions -> FFTOptions #
Read FFTOptions Source #
Instance details Defined in Data.Functor.Deriving.Internal Methods readsPrec :: Int -> ReadS FFTOptions # readList :: ReadS [FFTOptions] # readPrec :: ReadPrec FFTOptions # readListPrec :: ReadPrec [FFTOptions] #
Show FFTOptions Source #
Instance details Defined in Data.Functor.Deriving.Internal Methods showsPrec :: Int -> FFTOptions -> ShowS # show :: FFTOptions -> String # showList :: [FFTOptions] -> ShowS #

defaultFFTOptions :: FFTOptions Source #

Conservative FFTOptions that doesn't attempt to use EmptyCase (to prevent users from having to enable that extension at use sites.)

`deriveTraversable` limitations

Be aware of the following potential gotchas:

If you are using the -XGADTs or -XExistentialQuantification extensions, an existential constraint cannot mention the last type variable. For example, data Illegal a = forall a. Show a => Illegal a cannot have a derived Traversable instance.
Type variables of kind * -> * are assumed to have Traversable constraints. If this is not desirable, use makeTraverse.

Traversable

FFTOptions

deriveTraversable limitations

`Traversable`

`FFTOptions`

`deriveTraversable` limitations