@@ -1,8 +1,14 @@
1−{-# LANGUAGE FlexibleContexts, UndecidableInstances, TypeOperators, DataKinds, TypeFamilies, ScopedTypeVariables#-}
1+#if __GLASGOW_HASKELL__ >= 806
2+{-# OPTIONS_GHC -Wno-star-is-type #-}
4+#if __GLASGOW_HASKELL__ >= 800
5+{-# OPTIONS_GHC -Wno-unticked-promoted-constructors #-}
5−Generic implementation of the 'arbitrary' method. Example usage:
10+This module is a generic implementation of the 'arbitrary' method. Example
8data Foo = Foo
14data Foo = Foo
@@ -27,51 +33,202 @@ data Foo = Foo
28The generated 'arbitrary' method is equivalent to
34The generated 'arbitrary' method is equivalent to
30−@Foo <$> arbitrary <*> arbitrary@.
37+Foo '<$>' arbitrary '<*>' arbitrary
40+It can also handle a recursive types problem. Assuming a type
50+instance Arbitrary R where
51+ arbitrary = genericArbitrary
52+ shrink = genericShrink
55+If you try to compile this you will get a type level error
57+> • R refers to itself in all constructors
59+Which means that there is no finite term for @R@ because it is recursive. But,
60+if you correct the definition of @R@ like this.
67+Then it will compile. And the @arbitrary@ generated will not hang forever, because
68+it respects the @size@ parameter.
70+There is a limitation of recursion detection:
74+ deriving (Eq, Ord, Show, Generic)
75+ deriving anyclass NFData
76+ deriving Arbitrary via (GenericArbitrary R1)
79+ deriving (Eq, Ord, Show, Generic)
80+ deriving anyclass NFData
81+ deriving Arbitrary via (GenericArbitrary R2)
84+This code will compile and the @arbitrary@ generated will always hang. Yes,
85+there is a problem with mutually recursive types.
87+Now lets see an example of datatype with parameters
91+ deriving (Eq, Ord, Show)
92+ deriving anyclass NFData
95+instance (Arbitrary a) => Arbitrary (A a) where
96+ arbitrary = genericArbitrary
97+ shrink = genericShrink
100+It should work from first glance, but when compile it will throw an error:
103+ • Could not deduce (Test.QuickCheck.Arbitrary.Generic.GArbitrary
106+ ('GHC.Generics.MetaData "A" "ParametersTest" "main" 'False)
108+ ('GHC.Generics.MetaCons "A" 'GHC.Generics.PrefixI 'False)
110+ ('GHC.Generics.MetaSel
112+ 'GHC.Generics.NoSourceUnpackedness
113+ 'GHC.Generics.NoSourceStrictness
114+ 'GHC.Generics.DecidedLazy)
115+ (GHC.Generics.Rec0 a))))
116+ (TypesDiffer (A a) a))
117+ arising from a use of ‘genericArbitrary’
120+Here the @TypesDiffer@ is a type familty dealing with recursive types and
121+helping us to eliminate inproper instances. To convince the compiller, that the
122+@a@ parameter is not an @A a@ we must fix the instance with additional constraint
125+instance (Arg (A a) a, Arbitrary a) => Arbitrary (A a) where
126+ arbitrary = genericArbitrary
127+ shrink = genericShrink
130+Now everything compiles and works as expected.
34module Test.QuickCheck.Arbitrary.Generic
134module Test.QuickCheck.Arbitrary.Generic
137+#if MIN_VERSION_QuickCheck(2, 14, 0)
35− ( GenericArbitrary(..)
138+ , GenericArbitrary(..)
36 , Arbitrary(..)
151 , Arbitrary(..)
38 , genericShrink
152 , genericShrink
41−import Control.Applicative
155+import Control.Applicative
42−import Data.Coerce (coerce)
43−import Data.Proxy
156+import Data.Proxy
157+import Data.Type.Bool
44−import GHC.Generics as G
158+import GHC.Generics as G
45−import GHC.TypeLits
159+import GHC.TypeLits
46−import Test.QuickCheck as QC
161+import Test.QuickCheck as QC
162+#if MIN_VERSION_QuickCheck(2, 14, 0)
163+import Data.Coerce (coerce)
47−import Test.QuickCheck.Arbitrary (GSubterms, RecursivelyShrink)
164+import Test.QuickCheck.Arbitrary (GSubterms, RecursivelyShrink)
168+-- | Newtype for @DerivingVia@
176+-- } deriving (Generic)
177+-- deriving (Arbitrary) via GenericArbitrary Foo
49newtype GenericArbitrary a = GenericArbitrary { unGenericArbitrary :: a }
181newtype GenericArbitrary a = GenericArbitrary { unGenericArbitrary :: a }
50 deriving (Show, Eq)
182 deriving (Show, Eq)
53 ( Generic a,
185 ( Generic a,
54− GArbitrary (Rep a),
186+ GArbitrary a (Rep a) some,
55 RecursivelyShrink (Rep a),
187 RecursivelyShrink (Rep a),
56 GSubterms (Rep a) a
188 GSubterms (Rep a) a
57 ) => Arbitrary (GenericArbitrary a) where
189 ) => Arbitrary (GenericArbitrary a) where
58 arbitrary = coerce (genericArbitrary :: Gen a)
190 arbitrary = coerce (genericArbitrary :: Gen a)
59 shrink = coerce (genericShrink :: a -> [a])
191 shrink = coerce (genericShrink :: a -> [a])
61−class GArbitrary a where
194+-- | Constraint helper for types with parameters
62− gArbitrary :: QC.Gen (a x)
195+--
200+-- deriving (Generic)
201+-- instance (Arg (A a) a, Arbitrary a) => Arbitrary (A a) where
202+-- arbitrary = genericArbitrary
203+-- shrink = genericShrink
64−instance GArbitrary G.U1 where
208+type Arg self field = (TypesDiffer self field ~ 'True)
65− gArbitrary = pure G.U1
67−instance Arbitrary c => GArbitrary (G.K1 i c) where
210+type family TypesDiffer a b where
68− gArbitrary = G.K1 <$> arbitrary
211+ TypesDiffer a a = 'False
212+ TypesDiffer a b = 'True
70−instance GArbitrary f => GArbitrary (G.M1 i c f) where
214+type family AllFieldsFinal self (a :: * -> *) :: Bool where
71− gArbitrary = G.M1 <$> gArbitrary
215+ AllFieldsFinal self U1 = 'True
216+ AllFieldsFinal self (a :*: b) = AllFieldsFinal self a && AllFieldsFinal self b
217+ AllFieldsFinal self (M1 S t (K1 R field)) = TypesDiffer self field
73−instance (GArbitrary a, GArbitrary b) => GArbitrary (a G.:*: b) where
219+type family Finite self (a :: * -> *) :: Bool where
74− gArbitrary = liftA2 (G.:*:) gArbitrary gArbitrary
220+ Finite self U1 = 'True
221+ Finite self (K1 R field) = TypesDiffer self field
222+ Finite self (a :*: b) = Finite self a && Finite self b
223+ Finite self (M1 D t f) = Finite self f
224+ Finite self (a :+: b) = Finite self a || Finite self b
225+ Finite self (M1 C c f) = AllFieldsFinal self f
226+ Finite self (M1 S s f) = Finite self f
228+type family ArgumentsCount (a :: * -> *) :: Nat where
229+ ArgumentsCount U1 = 1
230+ ArgumentsCount (M1 S s f) = 1
231+ ArgumentsCount (a :*: b) = (ArgumentsCount a) + (ArgumentsCount b)
76-- | Calculates count of constructors encoded by particular ':+:'.
233-- | Calculates count of constructors encoded by particular ':+:'.
77-- Internal use only.
234-- Internal use only.
@@ -79,14 +236,140 @@ type family SumLen a :: Nat where
79 SumLen (a G.:+: b) = (SumLen a) + (SumLen b)
236 SumLen (a G.:+: b) = (SumLen a) + (SumLen b)
80 SumLen a = 1
237 SumLen a = 1
239+-- | Generic arbitrary.
242+-- * self: the ADT we generating instance for
243+-- * a: some part of the `Rep self`
244+-- * finite: Is `a` finite? Infinite type has no finite values (like Stream)
245+class (Finite self a ~ finite) => GArbitrary self a (finite :: Bool) where
246+ gArbitrary :: Proxy self -> QC.Gen (a x)
249+ ( GArbitrary self (M1 C c f) 'True
250+ ) => GArbitrary self (M1 D t (M1 C c f)) 'True where
251+ gArbitrary _ = M1 <$> gArbitrary (Proxy :: Proxy self)
253+-- | The constructor meta information
255+ ( GArbitrary self f some
256+ , KnownNat (ArgumentsCount f)
257+ , AllFieldsFinal self f ~ some
258+ ) => GArbitrary self (M1 C c f) some where
259+ gArbitrary _ = M1 <$> scale predNat (gArbitrary (Proxy :: Proxy self))
261+ argumentsCount = fromIntegral $ natVal (Proxy :: Proxy (ArgumentsCount f))
262+ predNat n = max 0 $ if argumentsCount > 1
263+ then n `div` argumentsCount
266+-- | Unit type instance
267+instance GArbitrary self U1 'True where
268+ gArbitrary _ = pure U1
270+-- | Constructor field meta information
271+instance GArbitrary self f some => GArbitrary self (M1 S t f) some where
272+ gArbitrary _ = M1 <$> gArbitrary (Proxy :: Proxy self)
274+-- | Data of the constructor field
277+ , Finite self (K1 R t) ~ some
278+ ) => GArbitrary self (K1 R t) some where
279+ gArbitrary _ = K1 <$> arbitrary
283+ ( GArbitrary self a af
284+ , GArbitrary self b bf
286+ ) => GArbitrary self (a :*: b) some where
287+ gArbitrary _ = liftA2 (:*:)
288+ (gArbitrary (Proxy :: Proxy self)) (gArbitrary (Proxy :: Proxy self))
290+#if __GLASGOW_HASKELL__ >= 800
292+ ( TypeError (ShowType self :<>: Text " refers to itself in all constructors")
293+ , AllFieldsFinal self f ~ 'False
294+ ) => GArbitrary self (M1 D t (M1 C c f)) 'False where
295+ gArbitrary _ = error "Unreachable"
298+-- | ADT declaration with multiple constructors
300+ ( FiniteSum self a b af bf
301+ , GArbitrary self (a :+: b) 'True
302+ ) => GArbitrary self (M1 D t (a :+: b)) 'True where
303+ gArbitrary _ = sized $ \s -> M1 <$>
305+ then gArbitrary (Proxy :: Proxy self)
306+ else oneof (finiteSum (Proxy :: Proxy self))
308+-- | Any sum inside of declaration
310+ ( GArbitrary self a af, GArbitrary self b bf
82−instance (GArbitrary a, GArbitrary b, KnownNat (SumLen a), KnownNat (SumLen b)
311+ , KnownNat (SumLen a), KnownNat (SumLen b)
83− ) => GArbitrary (a G.:+: b) where
313+ ) => GArbitrary self (a :+: b) some where
84− gArbitrary = frequency
314+ gArbitrary _ = frequency
85− [ (lfreq, G.L1 <$> QC.scale pred gArbitrary)
315+ [ (lfreq, G.L1 <$> gArbitrary (Proxy :: Proxy self))
86− , (rfreq, G.R1 <$> QC.scale pred gArbitrary) ]
316+ , (rfreq, G.R1 <$> gArbitrary (Proxy :: Proxy self)) ]
88 lfreq = fromIntegral $ natVal (Proxy :: Proxy (SumLen a))
318 lfreq = fromIntegral $ natVal (Proxy :: Proxy (SumLen a))
89 rfreq = fromIntegral $ natVal (Proxy :: Proxy (SumLen b))
319 rfreq = fromIntegral $ natVal (Proxy :: Proxy (SumLen b))
322+ ( Finite self a ~ af, Finite self b ~ bf
323+ ) => FiniteSum self (a :: * -> *) (b :: * -> *) af bf where
324+ finiteSum :: Proxy self -> [Gen ((a :+: b) p)]
327+ ( FiniteSumElem self a, FiniteSumElem self b
328+ , Finite self a ~ 'True
329+ , Finite self b ~ 'True
330+ ) => FiniteSum self a b 'True 'True where
331+ finiteSum _ = concat
332+ [ fmap L1 <$> finiteElem (Proxy :: Proxy self)
333+ , fmap R1 <$> finiteElem (Proxy :: Proxy self)]
336+ ( FiniteSumElem self a
337+ , Finite self a ~ 'True
338+ , Finite self b ~ 'False
339+ ) => FiniteSum self a b 'True 'False where
340+ finiteSum _ = fmap L1 <$> finiteElem (Proxy :: Proxy self)
343+ ( FiniteSumElem self b
344+ , Finite self a ~ 'False
345+ , Finite self b ~ 'True
346+ ) => FiniteSum self a b 'False 'True where
347+ finiteSum _ = fmap R1 <$> finiteElem (Proxy :: Proxy self)
349+class FiniteSumElem self a where
350+ finiteElem :: Proxy self -> [Gen (a p)]
353+ ( FiniteSum self a b af bf
354+ ) => FiniteSumElem self (a :+: b) where
355+ finiteElem _ = finiteSum (Proxy :: Proxy self)
358+ ( GArbitrary self (M1 C c f) 'True
359+ ) => FiniteSumElem self (M1 C c f) where
360+ finiteElem _ = [gArbitrary (Proxy :: Proxy self)]
363+#if __GLASGOW_HASKELL__ >= 800
365+ ( TypeError (ShowType self :<>: Text " refers to itself in all constructors")
366+ , (Finite self a || Finite self b) ~ 'False
367+ ) => GArbitrary self (M1 D t (a :+: b)) 'False where
368+ gArbitrary _ = error "Unreachable"
91−genericArbitrary :: (Generic a, GArbitrary ga, ga ~ G.Rep a) => Gen a
373+ . (Generic a, GArbitrary a ga some, ga ~ Rep a)
92−genericArbitrary = G.to <$> gArbitrary
375+genericArbitrary = G.to <$> gArbitrary (Proxy :: Proxy a)