Copyright | (c) 2010-2011 Patrick Bahr |
---|---|
License | BSD3 |
Maintainer | Patrick Bahr <paba@diku.dk> |
Stability | experimental |
Portability | non-portable (GHC Extensions) |
Safe Haskell | None |
Language | Haskell98 |
This module contains functionality for automatically deriving boilerplate
code using Template Haskell. Examples include instances of Functor
,
Foldable
, and Traversable
.
- derive :: [Name -> Q [Dec]] -> [Name] -> Q [Dec]
- class ShowF f where
- makeShowF :: Name -> Q [Dec]
- class ShowConstr f where
- makeShowConstr :: Name -> Q [Dec]
- class EqF f where
- makeEqF :: Name -> Q [Dec]
- class EqF f => OrdF f where
- makeOrdF :: Name -> Q [Dec]
- class Foldable t
- makeFoldable :: Name -> Q [Dec]
- class (Functor t, Foldable t) => Traversable t
- makeTraversable :: Name -> Q [Dec]
- makeHaskellStrict :: Name -> Q [Dec]
- haskellStrict :: (Monad m, HaskellStrict f, f :<: (m :+: g)) => f (TermT m g) -> TermT m g
- haskellStrict' :: (Monad m, HaskellStrict f, f :<: (m :+: g)) => f (TermT m g) -> TermT m g
- class ArbitraryF f where
- makeArbitraryF :: Name -> Q [Dec]
- class Arbitrary a where
- makeArbitrary :: Name -> Q [Dec]
- class NFData a where
- makeNFData :: Name -> Q [Dec]
- class NFDataF f where
- makeNFDataF :: Name -> Q [Dec]
- smartConstructors :: Name -> Q [Dec]
- smartAConstructors :: Name -> Q [Dec]
- liftSum :: Name -> Q [Dec]
Documentation
derive :: [Name -> Q [Dec]] -> [Name] -> Q [Dec] Source #
Helper function for generating a list of instances for a list of named
signatures. For example, in order to derive instances Functor
and
ShowF
for a signature Exp
, use derive as follows (requires Template
Haskell):
$(derive [makeFunctor, makeShowF] [''Exp])
Derive boilerplate instances for compositional data type signatures.
ShowF
Signature printing. An instance ShowF f
gives rise to an instance
Show (Term f)
.
makeShowF :: Name -> Q [Dec] Source #
Derive an instance of ShowF
for a type constructor of any first-order kind
taking at least one argument.
makeShowConstr :: Name -> Q [Dec] Source #
Derive an instance of showConstr
for a type constructor of any first-order kind
taking at least one argument.
EqF
Signature equality. An instance EqF f
gives rise to an instance
Eq (Term f)
.
makeEqF :: Name -> Q [Dec] Source #
Derive an instance of EqF
for a type constructor of any first-order kind
taking at least one argument.
OrdF
class EqF f => OrdF f where Source #
Signature ordering. An instance OrdF f
gives rise to an instance
Ord (Term f)
.
makeOrdF :: Name -> Q [Dec] Source #
Derive an instance of OrdF
for a type constructor of any first-order kind
taking at least one argument.
Foldable
Data structures that can be folded.
For example, given a data type
data Tree a = Empty | Leaf a | Node (Tree a) a (Tree a)
a suitable instance would be
instance Foldable Tree where foldMap f Empty = mempty foldMap f (Leaf x) = f x foldMap f (Node l k r) = foldMap f l `mappend` f k `mappend` foldMap f r
This is suitable even for abstract types, as the monoid is assumed
to satisfy the monoid laws. Alternatively, one could define foldr
:
instance Foldable Tree where foldr f z Empty = z foldr f z (Leaf x) = f x z foldr f z (Node l k r) = foldr f (f k (foldr f z r)) l
Foldable
instances are expected to satisfy the following laws:
foldr f z t = appEndo (foldMap (Endo . f) t ) z
foldl f z t = appEndo (getDual (foldMap (Dual . Endo . flip f) t)) z
fold = foldMap id
sum
, product
, maximum
, and minimum
should all be essentially
equivalent to foldMap
forms, such as
sum = getSum . foldMap Sum
but may be less defined.
If the type is also a Functor
instance, it should satisfy
foldMap f = fold . fmap f
which implies that
foldMap f . fmap g = foldMap (f . g)
makeFoldable :: Name -> Q [Dec] Source #
Derive an instance of Foldable
for a type constructor of any first-order
kind taking at least one argument.
Traversable
class (Functor t, Foldable t) => Traversable t #
Functors representing data structures that can be traversed from left to right.
A definition of traverse
must satisfy the following laws:
- naturality
t .
for every applicative transformationtraverse
f =traverse
(t . f)t
- identity
traverse
Identity = Identity- composition
traverse
(Compose .fmap
g . f) = Compose .fmap
(traverse
g) .traverse
f
A definition of sequenceA
must satisfy the following laws:
- naturality
t .
for every applicative transformationsequenceA
=sequenceA
.fmap
tt
- identity
sequenceA
.fmap
Identity = Identity- composition
sequenceA
.fmap
Compose = Compose .fmap
sequenceA
.sequenceA
where an applicative transformation is a function
t :: (Applicative f, Applicative g) => f a -> g a
preserving the Applicative
operations, i.e.
and the identity functor Identity
and composition of functors Compose
are defined as
newtype Identity a = Identity a instance Functor Identity where fmap f (Identity x) = Identity (f x) instance Applicative Identity where pure x = Identity x Identity f <*> Identity x = Identity (f x) newtype Compose f g a = Compose (f (g a)) instance (Functor f, Functor g) => Functor (Compose f g) where fmap f (Compose x) = Compose (fmap (fmap f) x) instance (Applicative f, Applicative g) => Applicative (Compose f g) where pure x = Compose (pure (pure x)) Compose f <*> Compose x = Compose ((<*>) <$> f <*> x)
(The naturality law is implied by parametricity.)
Instances are similar to Functor
, e.g. given a data type
data Tree a = Empty | Leaf a | Node (Tree a) a (Tree a)
a suitable instance would be
instance Traversable Tree where traverse f Empty = pure Empty traverse f (Leaf x) = Leaf <$> f x traverse f (Node l k r) = Node <$> traverse f l <*> f k <*> traverse f r
This is suitable even for abstract types, as the laws for <*>
imply a form of associativity.
The superclass instances should satisfy the following:
- In the
Functor
instance,fmap
should be equivalent to traversal with the identity applicative functor (fmapDefault
). - In the
Foldable
instance,foldMap
should be equivalent to traversal with a constant applicative functor (foldMapDefault
).
makeTraversable :: Name -> Q [Dec] Source #
Derive an instance of Traversable
for a type constructor of any
first-order kind taking at least one argument.
HaskellStrict
makeHaskellStrict :: Name -> Q [Dec] Source #
Derive an instance of HaskellStrict
for a type constructor of any
first-order kind taking at least one argument.
haskellStrict' :: (Monad m, HaskellStrict f, f :<: (m :+: g)) => f (TermT m g) -> TermT m g Source #
Arbitrary
class ArbitraryF f where Source #
Signature arbitration. An instance ArbitraryF f
gives rise to an instance
Arbitrary (Term f)
.
makeArbitraryF :: Name -> Q [Dec] Source #
Derive an instance of ArbitraryF
for a type constructor of any
first-order kind taking at least one argument. It is necessary that
all types that are used by the data type definition are themselves
instances of Arbitrary
.
Random generation and shrinking of values.
A generator for values of the given type.
Produces a (possibly) empty list of all the possible immediate shrinks of the given value. The default implementation returns the empty list, so will not try to shrink the value.
Most implementations of shrink
should try at least three things:
- Shrink a term to any of its immediate subterms.
- Recursively apply
shrink
to all immediate subterms. - Type-specific shrinkings such as replacing a constructor by a simpler constructor.
For example, suppose we have the following implementation of binary trees:
data Tree a = Nil | Branch a (Tree a) (Tree a)
We can then define shrink
as follows:
shrink Nil = [] shrink (Branch x l r) = -- shrink Branch to Nil [Nil] ++ -- shrink to subterms [l, r] ++ -- recursively shrink subterms [Branch x' l' r' | (x', l', r') <- shrink (x, l, r)]
There are a couple of subtleties here:
- QuickCheck tries the shrinking candidates in the order they
appear in the list, so we put more aggressive shrinking steps
(such as replacing the whole tree by
Nil
) before smaller ones (such as recursively shrinking the subtrees). - It is tempting to write the last line as
[Branch x' l' r' | x' <- shrink x, l' <- shrink l, r' <- shrink r]
but this is the wrong thing! It will force QuickCheck to shrinkx
,l
andr
in tandem, and shrinking will stop once one of the three is fully shrunk.
There is a fair bit of boilerplate in the code above.
We can avoid it with the help of some generic functions;
note that these only work on GHC 7.2 and above.
The function genericShrink
tries shrinking a term to all of its
subterms and, failing that, recursively shrinks the subterms.
Using it, we can define shrink
as:
shrink x = shrinkToNil x ++ genericShrink x where shrinkToNil Nil = [] shrinkToNil (Branch _ l r) = [Nil]
genericShrink
is a combination of subterms
, which shrinks
a term to any of its subterms, and recursivelyShrink
, which shrinks
all subterms of a term. These may be useful if you need a bit more
control over shrinking than genericShrink
gives you.
A final gotcha: we cannot define shrink
as simply
as this shrinks shrink
x = Nil:genericShrink
xNil
to Nil
, and shrinking will go into an
infinite loop.
If all this leaves you bewildered, you might try
to begin with,
after deriving shrink
= genericShrink
Generic
for your type. However, if your data type has any
special invariants, you will need to check that genericShrink
can't break those invariants.
A class of types that can be fully evaluated.
Since: 1.1.0.0
rnf
should reduce its argument to normal form (that is, fully
evaluate all sub-components), and then return '()'.
Generic
NFData
deriving
Starting with GHC 7.2, you can automatically derive instances
for types possessing a Generic
instance.
{-# LANGUAGE DeriveGeneric #-} import GHC.Generics (Generic) import Control.DeepSeq data Foo a = Foo a String deriving (Eq, Generic) instance NFData a => NFData (Foo a) data Colour = Red | Green | Blue deriving Generic instance NFData Colour
Starting with GHC 7.10, the example above can be written more
concisely by enabling the new DeriveAnyClass
extension:
{-# LANGUAGE DeriveGeneric, DeriveAnyClass #-} import GHC.Generics (Generic) import Control.DeepSeq data Foo a = Foo a String deriving (Eq, Generic, NFData) data Colour = Red | Green | Blue deriving (Generic, NFData)
Compatibility with previous deepseq
versions
Prior to version 1.4.0.0, the default implementation of the rnf
method was defined as
rnf
a =seq
a ()
However, starting with deepseq-1.4.0.0
, the default
implementation is based on DefaultSignatures
allowing for
more accurate auto-derived NFData
instances. If you need the
previously used exact default rnf
method implementation
semantics, use
instance NFData Colour where rnf x = seq x ()
or alternatively
{-# LANGUAGE BangPatterns #-} instance NFData Colour where rnf !_ = ()
NFData Bool | |
NFData Char | |
NFData Double | |
NFData Float | |
NFData Int | |
NFData Int8 | |
NFData Int16 | |
NFData Int32 | |
NFData Int64 | |
NFData Integer | |
NFData Word | |
NFData Word8 | |
NFData Word16 | |
NFData Word32 | |
NFData Word64 | |
NFData CallStack | Since: 1.4.2.0 |
NFData TypeRep | NOTE: Only defined for Since: 1.4.0.0 |
NFData () | |
NFData TyCon | NOTE: Only defined for Since: 1.4.0.0 |
NFData Natural | Since: 1.4.0.0 |
NFData Void | Since: 1.4.0.0 |
NFData Version | Since: 1.3.0.0 |
NFData Unique | Since: 1.4.0.0 |
NFData ThreadId | Since: 1.4.0.0 |
NFData ExitCode | Since: 1.4.2.0 |
NFData CChar | Since: 1.4.0.0 |
NFData CSChar | Since: 1.4.0.0 |
NFData CUChar | Since: 1.4.0.0 |
NFData CShort | Since: 1.4.0.0 |
NFData CUShort | Since: 1.4.0.0 |
NFData CInt | Since: 1.4.0.0 |
NFData CUInt | Since: 1.4.0.0 |
NFData CLong | Since: 1.4.0.0 |
NFData CULong | Since: 1.4.0.0 |
NFData CLLong | Since: 1.4.0.0 |
NFData CULLong | Since: 1.4.0.0 |
NFData CFloat | Since: 1.4.0.0 |
NFData CDouble | Since: 1.4.0.0 |
NFData CPtrdiff | Since: 1.4.0.0 |
NFData CSize | Since: 1.4.0.0 |
NFData CWchar | Since: 1.4.0.0 |
NFData CSigAtomic | Since: 1.4.0.0 |
NFData CClock | Since: 1.4.0.0 |
NFData CTime | Since: 1.4.0.0 |
NFData CUSeconds | Since: 1.4.0.0 |
NFData CSUSeconds | Since: 1.4.0.0 |
NFData CFile | Since: 1.4.0.0 |
NFData CFpos | Since: 1.4.0.0 |
NFData CJmpBuf | Since: 1.4.0.0 |
NFData CIntPtr | Since: 1.4.0.0 |
NFData CUIntPtr | Since: 1.4.0.0 |
NFData CIntMax | Since: 1.4.0.0 |
NFData CUIntMax | Since: 1.4.0.0 |
NFData All | Since: 1.4.0.0 |
NFData Any | Since: 1.4.0.0 |
NFData Fingerprint | Since: 1.4.0.0 |
NFData SrcLoc | Since: 1.4.2.0 |
NFData IntSet | |
NFData Doc | |
NFData TextDetails | |
NFData LocalTime | |
NFData ZonedTime | |
NFData a => NFData [a] | |
NFData a => NFData (Maybe a) | |
NFData a => NFData (Ratio a) | |
NFData (Ptr a) | Since: 1.4.2.0 |
NFData (FunPtr a) | Since: 1.4.2.0 |
NFData a => NFData (Identity a) | Since: 1.4.0.0 |
NFData a => NFData (Min a) | Since: 1.4.2.0 |
NFData a => NFData (Max a) | Since: 1.4.2.0 |
NFData a => NFData (First a) | Since: 1.4.2.0 |
NFData a => NFData (Last a) | Since: 1.4.2.0 |
NFData m => NFData (WrappedMonoid m) | Since: 1.4.2.0 |
NFData a => NFData (Option a) | Since: 1.4.2.0 |
NFData a => NFData (NonEmpty a) | Since: 1.4.2.0 |
NFData (Fixed a) | Since: 1.3.0.0 |
NFData a => NFData (Complex a) | |
NFData (StableName a) | Since: 1.4.0.0 |
NFData a => NFData (ZipList a) | Since: 1.4.0.0 |
NFData a => NFData (Dual a) | Since: 1.4.0.0 |
NFData a => NFData (Sum a) | Since: 1.4.0.0 |
NFData a => NFData (Product a) | Since: 1.4.0.0 |
NFData a => NFData (First a) | Since: 1.4.0.0 |
NFData a => NFData (Last a) | Since: 1.4.0.0 |
NFData (IORef a) | NOTE: Only strict in the reference and not the referenced value. Since: 1.4.2.0 |
NFData a => NFData (Down a) | Since: 1.4.0.0 |
NFData (MVar a) | NOTE: Only strict in the reference and not the referenced value. Since: 1.4.2.0 |
NFData a => NFData (Digit a) | |
NFData a => NFData (Node a) | |
NFData a => NFData (Elem a) | |
NFData a => NFData (FingerTree a) | |
NFData a => NFData (IntMap a) | |
NFData a => NFData (Tree a) | |
NFData a => NFData (Seq a) | |
NFData a => NFData (Set a) | |
NFData a => NFData (Doc a) | |
NFData a => NFData (AnnotDetails a) | |
NFData a => NFData (HashSet a) | |
NFData (a -> b) | This instance is for convenience and consistency with Since: 1.3.0.0 |
(NFData a, NFData b) => NFData (Either a b) | |
(NFData a, NFData b) => NFData (a, b) | |
(NFData a, NFData b) => NFData (Array a b) | |
(NFData a, NFData b) => NFData (Arg a b) | Since: 1.4.2.0 |
NFData (Proxy k a) | Since: 1.4.0.0 |
NFData (STRef s a) | NOTE: Only strict in the reference and not the referenced value. Since: 1.4.2.0 |
(NFData k, NFData a) => NFData (Map k a) | |
(NFData k, NFData v) => NFData (Leaf k v) | |
(NFData k, NFData v) => NFData (HashMap k v) | |
(NFData a, NFData b, NFData c) => NFData (a, b, c) | |
NFData a => NFData (Const k a b) | Since: 1.4.0.0 |
(NFData a, NFData b, NFData c, NFData d) => NFData (a, b, c, d) | |
(NFData a1, NFData a2, NFData a3, NFData a4, NFData a5) => NFData (a1, a2, a3, a4, a5) | |
(NFData a1, NFData a2, NFData a3, NFData a4, NFData a5, NFData a6) => NFData (a1, a2, a3, a4, a5, a6) | |
(NFData a1, NFData a2, NFData a3, NFData a4, NFData a5, NFData a6, NFData a7) => NFData (a1, a2, a3, a4, a5, a6, a7) | |
(NFData a1, NFData a2, NFData a3, NFData a4, NFData a5, NFData a6, NFData a7, NFData a8) => NFData (a1, a2, a3, a4, a5, a6, a7, a8) | |
(NFData a1, NFData a2, NFData a3, NFData a4, NFData a5, NFData a6, NFData a7, NFData a8, NFData a9) => NFData (a1, a2, a3, a4, a5, a6, a7, a8, a9) | |
DeepSeq
class NFDataF f where Source #
Signature normal form. An instance NFDataF f
gives rise to an instance
NFData (Term f)
.
makeNFDataF :: Name -> Q [Dec] Source #
Derive an instance of NFDataF
for a type constructor of any first-order
kind taking at least one argument.
Smart Constructors
smartConstructors :: Name -> Q [Dec] Source #
Derive smart constructors for a type constructor of any first-order kind
taking at least one argument. The smart constructors are similar to the
ordinary constructors, but an inject
is automatically inserted.
Smart Constructors w/ Annotations
smartAConstructors :: Name -> Q [Dec] Source #
Derive smart constructors with products for a type constructor of any
parametric kind taking at least one argument. The smart constructors are
similar to the ordinary constructors, but an injectA
is automatically
inserted.