@@ -1,14 +1,8 @@
1−#if __GLASGOW_HASKELL__ >= 806
2−{-# OPTIONS_GHC -Wno-star-is-type #-}
3−#endif
4−#if __GLASGOW_HASKELL__ >= 800
5−{-# OPTIONS_GHC -Wno-unticked-promoted-constructors #-}
6−#endif
1+{-# LANGUAGE FlexibleContexts, UndecidableInstances, TypeOperators, DataKinds, TypeFamilies, ScopedTypeVariables#-}
72
8−{-|
3+{- |
94
10−This module is a generic implementation of the 'arbitrary' method. Example
11−usage:
5+Generic implementation of the 'arbitrary' method. Example usage:
126
137@
148data Foo = Foo
@@ -33,202 +27,51 @@ data Foo = Foo
3327
3428The generated 'arbitrary' method is equivalent to
3529
36−@
37−Foo '<$>' arbitrary '<*>' arbitrary
38−@.
39−
40−It can also handle a recursive types problem. Assuming a type
41−
42−@
43−data R = R R
44− deriving Generic
45−@
46−
47−there is no instance
48−
49−@
50−instance Arbitrary R where
51− arbitrary = genericArbitrary
52− shrink = genericShrink
53−@
54−
55−If you try to compile this you will get a type level error
56−
57−> • R refers to itself in all constructors
58−
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.
61−
62−@
63−data R = R R | F
64− deriving Generic
65−@
66−
67−Then it will compile. And the @arbitrary@ generated will not hang forever, because
68−it respects the @size@ parameter.
69−
70−There is a limitation of recursion detection:
71−
72−@
73−data R1 = R1 R2
74− deriving (Eq, Ord, Show, Generic)
75− deriving anyclass NFData
76− deriving Arbitrary via (GenericArbitrary R1)
77−
78−data R2 = R2 R1
79− deriving (Eq, Ord, Show, Generic)
80− deriving anyclass NFData
81− deriving Arbitrary via (GenericArbitrary R2)
82−@
83−
84−This code will compile and the @arbitrary@ generated will always hang. Yes,
85−there is a problem with mutually recursive types.
86−
87−Now lets see an example of datatype with parameters
88−
89−@
90−data A a = A a
91− deriving (Eq, Ord, Show)
92− deriving anyclass NFData
93− deriving (Generic)
94−
95−instance (Arbitrary a) => Arbitrary (A a) where
96− arbitrary = genericArbitrary
97− shrink = genericShrink
98−@
99−
100−It should work from first glance, but when compile it will throw an error:
101−
102−@
103− • Could not deduce (Test.QuickCheck.Arbitrary.Generic.GArbitrary
104− (A a)
105− (GHC.Generics.D1
106− ('GHC.Generics.MetaData "A" "ParametersTest" "main" 'False)
107− (GHC.Generics.C1
108− ('GHC.Generics.MetaCons "A" 'GHC.Generics.PrefixI 'False)
109− (GHC.Generics.S1
110− ('GHC.Generics.MetaSel
111− 'Nothing
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’
118−@
119−
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
123−
124−@
125−instance (Arg (A a) a, Arbitrary a) => Arbitrary (A a) where
126− arbitrary = genericArbitrary
127− shrink = genericShrink
128−@
129−
130−Now everything compiles and works as expected.
30+@Foo <$> arbitrary <*> arbitrary@.
13131
13232-}
13333
13434module Test.QuickCheck.Arbitrary.Generic
135− ( -- * Main
136− genericArbitrary
137−#if MIN_VERSION_QuickCheck(2, 14, 0)
138− , GenericArbitrary(..)
139−#endif
140− , Arg
141− -- * Internal
142− , GArbitrary
143− , FiniteSum
144− , FiniteSumElem
145− , Finite
146− , AllFieldsFinal
147− , TypesDiffer
148− , ArgumentsCount
149− , SumLen
150− -- * Reexports
35+ ( GenericArbitrary(..)
15136 , Arbitrary(..)
37+ , genericArbitrary
15238 , genericShrink
15339 ) where
15440
155−import Control.Applicative
156−import Data.Proxy
157−import Data.Type.Bool
158−import GHC.Generics as G
159−import GHC.TypeLits
160−import Prelude
161−import Test.QuickCheck as QC
162−#if MIN_VERSION_QuickCheck(2, 14, 0)
163−import Data.Coerce (coerce)
164−import Test.QuickCheck.Arbitrary (GSubterms, RecursivelyShrink)
165−
166−
41+import Control.Applicative
42+import Data.Coerce (coerce)
43+import Data.Proxy
44+import GHC.Generics as G
45+import GHC.TypeLits
46+import Test.QuickCheck as QC
47+import Test.QuickCheck.Arbitrary (GSubterms, RecursivelyShrink)
16748
168−-- | Newtype for @DerivingVia@
169−--
170−-- Usage:
171−--
172−-- @
173−-- data Foo = Foo
174−-- { _fooX :: X
175−-- , _fooY :: Y
176−-- } deriving (Generic)
177−-- deriving (Arbitrary) via GenericArbitrary Foo
178−-- @
179−--
180−-- @since 1.0.0
18149newtype GenericArbitrary a = GenericArbitrary { unGenericArbitrary :: a }
18250 deriving (Show, Eq)
18351
18452instance
18553 ( Generic a,
186− GArbitrary a (Rep a) some,
54+ GArbitrary (Rep a),
18755 RecursivelyShrink (Rep a),
18856 GSubterms (Rep a) a
18957 ) => Arbitrary (GenericArbitrary a) where
19058 arbitrary = coerce (genericArbitrary :: Gen a)
19159 shrink = coerce (genericShrink :: a -> [a])
192−#endif
19360
194−-- | Constraint helper for types with parameters
195−--
196−-- Usage:
197−--
198−-- @
199−-- data A a = A a
200−-- deriving (Generic)
201−-- instance (Arg (A a) a, Arbitrary a) => Arbitrary (A a) where
202−-- arbitrary = genericArbitrary
203−-- shrink = genericShrink
204−-- @
205−--
206−-- @since 1.0.0
61+class GArbitrary a where
62+ gArbitrary :: QC.Gen (a x)
20763
208−type Arg self field = (TypesDiffer self field ~ 'True)
64+instance GArbitrary G.U1 where
65+ gArbitrary = pure G.U1
20966
210−type family TypesDiffer a b where
211− TypesDiffer a a = 'False
212− TypesDiffer a b = 'True
67+instance Arbitrary c => GArbitrary (G.K1 i c) where
68+ gArbitrary = G.K1 <$> arbitrary
21369
214−type family AllFieldsFinal self (a :: * -> *) :: Bool where
215− AllFieldsFinal self U1 = 'True
216− AllFieldsFinal self (a :*: b) = AllFieldsFinal self a && AllFieldsFinal self b
217− AllFieldsFinal self (M1 S t (K1 R field)) = TypesDiffer self field
70+instance GArbitrary f => GArbitrary (G.M1 i c f) where
71+ gArbitrary = G.M1 <$> gArbitrary
21872
219−type family Finite self (a :: * -> *) :: Bool where
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
227−
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)
73+instance (GArbitrary a, GArbitrary b) => GArbitrary (a G.:*: b) where
74+ gArbitrary = liftA2 (G.:*:) gArbitrary gArbitrary
23275
23376-- | Calculates count of constructors encoded by particular ':+:'.
23477-- Internal use only.
@@ -236,140 +79,14 @@ type family SumLen a :: Nat where
23679 SumLen (a G.:+: b) = (SumLen a) + (SumLen b)
23780 SumLen a = 1
23881
239−-- | Generic arbitrary.
240−--
241−-- Parameters are:
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)
247−
248−instance
249− ( GArbitrary self (M1 C c f) 'True
250− ) => GArbitrary self (M1 D t (M1 C c f)) 'True where
251− gArbitrary _ = M1 <$> gArbitrary (Proxy :: Proxy self)
252−
253−-- | The constructor meta information
254−instance
255− ( GArbitrary self f some
256− , KnownNat (ArgumentsCount f)
257− , AllFieldsFinal self f ~ some
258− ) => GArbitrary self (M1 C c f) some where
259− gArbitrary _ = M1 <$> scale predNat (gArbitrary (Proxy :: Proxy self))
260− where
261− argumentsCount = fromIntegral $ natVal (Proxy :: Proxy (ArgumentsCount f))
262− predNat n = max 0 $ if argumentsCount > 1
263− then n `div` argumentsCount
264− else pred n
265−
266−-- | Unit type instance
267−instance GArbitrary self U1 'True where
268− gArbitrary _ = pure U1
269−
270−-- | Constructor field meta information
271−instance GArbitrary self f some => GArbitrary self (M1 S t f) some where
272− gArbitrary _ = M1 <$> gArbitrary (Proxy :: Proxy self)
273−
274−-- | Data of the constructor field
275−instance
276− ( Arbitrary t
277− , Finite self (K1 R t) ~ some
278− ) => GArbitrary self (K1 R t) some where
279− gArbitrary _ = K1 <$> arbitrary
280−
281−-- | Product
282−instance
283− ( GArbitrary self a af
284− , GArbitrary self b bf
285− , (af && bf) ~ some
286− ) => GArbitrary self (a :*: b) some where
287− gArbitrary _ = liftA2 (:*:)
288− (gArbitrary (Proxy :: Proxy self)) (gArbitrary (Proxy :: Proxy self))
289−
290−#if __GLASGOW_HASKELL__ >= 800
291−instance
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"
296−#endif
297−
298−-- | ADT declaration with multiple constructors
299−instance
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 <$>
304− if s > 1
305− then gArbitrary (Proxy :: Proxy self)
306− else oneof (finiteSum (Proxy :: Proxy self))
307−
308−-- | Any sum inside of declaration
309−instance
310− ( GArbitrary self a af, GArbitrary self b bf
311− , KnownNat (SumLen a), KnownNat (SumLen b)
312− , (af || bf) ~ some
313− ) => GArbitrary self (a :+: b) some where
314− gArbitrary _ = frequency
315− [ (lfreq, G.L1 <$> gArbitrary (Proxy :: Proxy self))
316− , (rfreq, G.R1 <$> gArbitrary (Proxy :: Proxy self)) ]
82+instance (GArbitrary a, GArbitrary b, KnownNat (SumLen a), KnownNat (SumLen b)
83+ ) => GArbitrary (a G.:+: b) where
84+ gArbitrary = frequency
85+ [ (lfreq, G.L1 <$> QC.scale pred gArbitrary)
86+ , (rfreq, G.R1 <$> QC.scale pred gArbitrary) ]
31787 where
31888 lfreq = fromIntegral $ natVal (Proxy :: Proxy (SumLen a))
31989 rfreq = fromIntegral $ natVal (Proxy :: Proxy (SumLen b))
32090
321−class
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)]
325−
326−instance
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)]
334−
335−instance
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 <$> finiteElem (Proxy :: Proxy self)
341−
342−instance
343− ( FiniteSumElem self b
344− , Finite self a ~ 'False
345− , Finite self b ~ 'True
346− ) => FiniteSum self a b 'False 'True where
347− finiteSum _ = fmap R1 <$> finiteElem (Proxy :: Proxy self)
348−
349−class FiniteSumElem self a where
350− finiteElem :: Proxy self -> [Gen (a p)]
351−
352−instance
353− ( FiniteSum self a b af bf
354− ) => FiniteSumElem self (a :+: b) where
355− finiteElem _ = finiteSum (Proxy :: Proxy self)
356−
357−instance
358− ( GArbitrary self (M1 C c f) 'True
359− ) => FiniteSumElem self (M1 C c f) where
360− finiteElem _ = [gArbitrary (Proxy :: Proxy self)]
361−
362−
363−#if __GLASGOW_HASKELL__ >= 800
364−instance
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"
369−#endif
370−
371−genericArbitrary
372− :: forall a ga some
373− . (Generic a, GArbitrary a ga some, ga ~ Rep a)
374− => Gen a
375−genericArbitrary = G.to <$> gArbitrary (Proxy :: Proxy a)
91+genericArbitrary :: (Generic a, GArbitrary ga, ga ~ G.Rep a) => Gen a
92+genericArbitrary = G.to <$> gArbitrary