@@ -1,6 +1,14 @@
1−{- |
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
27
3−Generic implementation of the 'arbitrary' method. Example usage:
8+{-|
9+
10+This module is a generic implementation of the 'arbitrary' method. Example
11+usage:
412
513@
614data Foo = Foo
@@ -25,63 +33,203 @@ data Foo = Foo
2533
2634The generated 'arbitrary' method is equivalent to
2735
28−@Foo <$> arbitrary <*> arbitrary@.
36+@
37+Foo '<$>' 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.
29131
30132-}
31133
32134module Test.QuickCheck.Arbitrary.Generic
33− ( GenericArbitrary(..)
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
34151 , Arbitrary(..)
35− , genericArbitrary
36152 , genericShrink
37153 ) where
38154
39155import Control.Applicative
40−import Data.Coerce (coerce)
41156import Data.Proxy
42157import Data.Type.Bool
43158import GHC.Generics as G
44159import GHC.TypeLits
160+import Prelude
45161import Test.QuickCheck as QC
162+#if MIN_VERSION_QuickCheck(2, 14, 0)
163+import Data.Coerce (coerce)
46164import Test.QuickCheck.Arbitrary (GSubterms, RecursivelyShrink)
47−import TypeFun.Data.Eq
48−import TypeFun.Data.List
49165
166+
167+
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
50181newtype GenericArbitrary a = GenericArbitrary { unGenericArbitrary :: a }
51182 deriving (Show, Eq)
52183
53184instance
54185 ( Generic a,
55− GArbitrary a (Rep a) 'True,
186+ GArbitrary a (Rep a) some,
56187 RecursivelyShrink (Rep a),
57188 GSubterms (Rep a) a
58189 ) => Arbitrary (GenericArbitrary a) where
59190 arbitrary = coerce (genericArbitrary :: Gen a)
60191 shrink = coerce (genericShrink :: a -> [a])
192+#endif
61193
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
62207
63−-- type family FinalConstructors self (a :: * -> *) :: [* -> *] where
64−-- FinalConstructors self (a :+: b) =
65−-- FinalConstructors self a :++: FinalConstructors self b
66−-- FinalConstructors self (M1 C t f) = If (AllFieldsFinal self f) '[M1 C t f] '[]
208+type Arg self field = (TypesDiffer self field ~ 'True)
209+
210+type family TypesDiffer a b where
211+ TypesDiffer a a = 'False
212+ TypesDiffer a b = 'True
67213
68214type family AllFieldsFinal self (a :: * -> *) :: Bool where
69215 AllFieldsFinal self U1 = 'True
70216 AllFieldsFinal self (a :*: b) = AllFieldsFinal self a && AllFieldsFinal self b
71− AllFieldsFinal self (M1 S t (K1 R self)) = 'False
72− AllFieldsFinal self (M1 S t (K1 R other)) = 'True
217+ AllFieldsFinal self (M1 S t (K1 R field)) = TypesDiffer self field
73218
74219type family Finite self (a :: * -> *) :: Bool where
75220 Finite self U1 = 'True
76− -- | The constructor field is the ADT itself. Not finite.
77− Finite self (K1 R self) = 'False
78− Finite self (K1 R other) = 'True
221+ Finite self (K1 R field) = TypesDiffer self field
79222 Finite self (a :*: b) = Finite self a && Finite self b
80223 Finite self (M1 D t f) = Finite self f
81224 Finite self (a :+: b) = Finite self a || Finite self b
82225 Finite self (M1 C c f) = AllFieldsFinal self f
83226 Finite self (M1 S s f) = Finite self f
84227
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)
232+
85233-- | Calculates count of constructors encoded by particular ':+:'.
86234-- Internal use only.
87235type family SumLen a :: Nat where
@@ -95,37 +243,40 @@ type family SumLen a :: Nat where
95243-- * a: some part of the `Rep self`
96244-- * finite: Is `a` finite? Infinite type has no finite values (like Stream)
97245class (Finite self a ~ finite) => GArbitrary self a (finite :: Bool) where
98− gArbitrary :: QC.Gen (a x)
246+ gArbitrary :: Proxy self -> QC.Gen (a x)
99247
100248instance
101− ( GArbitrary self (C1 c f) 'True
102− ) => GArbitrary self (D1 t (C1 c f)) 'True where
103− gArbitrary = M1 <$> gArbitrary @self
249+ ( GArbitrary self (M1 C c f) 'True
250+ ) => GArbitrary self (M1 D t (M1 C c f)) 'True where
251+ gArbitrary _ = M1 <$> gArbitrary (Proxy :: Proxy self)
104252
105253-- | The constructor meta information
106254instance
107255 ( GArbitrary self f some
256+ , KnownNat (ArgumentsCount f)
108257 , AllFieldsFinal self f ~ some
109− ) => GArbitrary self (C1 c f) some where
110− gArbitrary = M1 <$> scale predNat (gArbitrary @self)
258+ ) => GArbitrary self (M1 C c f) some where
259+ gArbitrary _ = M1 <$> scale predNat (gArbitrary (Proxy :: Proxy self))
111260 where
112− predNat 0 = 0
113− predNat n = pred n
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
114265
115266-- | Unit type instance
116267instance GArbitrary self U1 'True where
117− gArbitrary = pure U1
268+ gArbitrary _ = pure U1
118269
119270-- | Constructor field meta information
120−instance GArbitrary self f some => GArbitrary self (S1 t f) some where
121− gArbitrary = M1 <$> gArbitrary @self
271+instance GArbitrary self f some => GArbitrary self (M1 S t f) some where
272+ gArbitrary _ = M1 <$> gArbitrary (Proxy :: Proxy self)
122273
123274-- | Data of the constructor field
124275instance
125276 ( Arbitrary t
126− , Finite self (Rec0 t) ~ some
127− ) => GArbitrary self (Rec0 t) some where
128− gArbitrary = K1 <$> arbitrary
277+ , Finite self (K1 R t) ~ some
278+ ) => GArbitrary self (K1 R t) some where
279+ gArbitrary _ = K1 <$> arbitrary
129280
130281-- | Product
131282instance
@@ -133,21 +284,26 @@ instance
133284 , GArbitrary self b bf
134285 , (af && bf) ~ some
135286 ) => GArbitrary self (a :*: b) some where
136− gArbitrary = liftA2 (:*:) (gArbitrary @self) (gArbitrary @self)
287+ gArbitrary _ = liftA2 (:*:)
288+ (gArbitrary (Proxy :: Proxy self)) (gArbitrary (Proxy :: Proxy self))
137289
290+#if __GLASGOW_HASKELL__ >= 800
138291instance
139292 ( TypeError (ShowType self :<>: Text " refers to itself in all constructors")
140293 , AllFieldsFinal self f ~ 'False
141− ) => GArbitrary self (D1 t (C1 c f)) 'False where
142− gArbitrary = error "Unreachable"
294+ ) => GArbitrary self (M1 D t (M1 C c f)) 'False where
295+ gArbitrary _ = error "Unreachable"
296+#endif
143297
144298-- | ADT declaration with multiple constructors
145299instance
146300 ( FiniteSum self a b af bf
147301 , GArbitrary self (a :+: b) 'True
148− ) => GArbitrary self (D1 t (a :+: b)) 'True where
149− gArbitrary = sized $ \s -> M1 <$>
150− if s > 1 then gArbitrary @self else finiteSum @self
302+ ) => GArbitrary self (M1 D t (a :+: b)) 'True where
303+ gArbitrary _ = sized $ \s -> M1 <$>
304+ if s > 1
305+ then gArbitrary (Proxy :: Proxy self)
306+ else oneof (finiteSum (Proxy :: Proxy self))
151307
152308-- | Any sum inside of declaration
153309instance
@@ -155,9 +311,9 @@ instance
155311 , KnownNat (SumLen a), KnownNat (SumLen b)
156312 , (af || bf) ~ some
157313 ) => GArbitrary self (a :+: b) some where
158− gArbitrary = frequency
159− [ (lfreq, G.L1 <$> gArbitrary @self)
160− , (rfreq, G.R1 <$> gArbitrary @self) ]
314+ gArbitrary _ = frequency
315+ [ (lfreq, G.L1 <$> gArbitrary (Proxy :: Proxy self))
316+ , (rfreq, G.R1 <$> gArbitrary (Proxy :: Proxy self)) ]
161317 where
162318 lfreq = fromIntegral $ natVal (Proxy :: Proxy (SumLen a))
163319 rfreq = fromIntegral $ natVal (Proxy :: Proxy (SumLen b))
@@ -165,52 +321,55 @@ instance
165321class
166322 ( Finite self a ~ af, Finite self b ~ bf
167323 ) => FiniteSum self (a :: * -> *) (b :: * -> *) af bf where
168− finiteSum :: Gen ((a :+: b) p)
324+ finiteSum :: Proxy self -> [Gen ((a :+: b) p)]
169325
170326instance
171327 ( FiniteSumElem self a, FiniteSumElem self b
172328 , Finite self a ~ 'True
173329 , Finite self b ~ 'True
174330 ) => FiniteSum self a b 'True 'True where
175− finiteSum = oneof
176− [ L1 <$> finiteElem @self
177− , R1 <$> finiteElem @self ]
331+ finiteSum _ = concat
332+ [ fmap L1 <$> finiteElem (Proxy :: Proxy self)
333+ , fmap R1 <$> finiteElem (Proxy :: Proxy self)]
178334
179335instance
180336 ( FiniteSumElem self a
181337 , Finite self a ~ 'True
182338 , Finite self b ~ 'False
183339 ) => FiniteSum self a b 'True 'False where
184− finiteSum = L1 <$> finiteElem @self
340+ finiteSum _ = fmap L1 <$> finiteElem (Proxy :: Proxy self)
185341
186342instance
187343 ( FiniteSumElem self b
188344 , Finite self a ~ 'False
189345 , Finite self b ~ 'True
190346 ) => FiniteSum self a b 'False 'True where
191− finiteSum = R1 <$> finiteElem @self
347+ finiteSum _ = fmap R1 <$> finiteElem (Proxy :: Proxy self)
192348
193349class FiniteSumElem self a where
194− finiteElem :: Gen (a p)
350+ finiteElem :: Proxy self -> [Gen (a p)]
195351
196352instance
197353 ( FiniteSum self a b af bf
198354 ) => FiniteSumElem self (a :+: b) where
199− finiteElem = finiteSum @self
355+ finiteElem _ = finiteSum (Proxy :: Proxy self)
200356
201357instance
202− ( GArbitrary self (C1 c f) 'True
203− ) => FiniteSumElem self (C1 c f) where
204− finiteElem = gArbitrary @self
358+ ( GArbitrary self (M1 C c f) 'True
359+ ) => FiniteSumElem self (M1 C c f) where
360+ finiteElem _ = [gArbitrary (Proxy :: Proxy self)]
361+
205362
363+#if __GLASGOW_HASKELL__ >= 800
206364instance
207365 ( TypeError (ShowType self :<>: Text " refers to itself in all constructors")
208366 , (Finite self a || Finite self b) ~ 'False
209− ) => GArbitrary self (D1 t (a :+: b)) 'False where
210− gArbitrary = error "Unreachable"
367+ ) => GArbitrary self (M1 D t (a :+: b)) 'False where
368+ gArbitrary _ = error "Unreachable"
369+#endif
211370
212371genericArbitrary
213372 :: forall a ga some
214373 . (Generic a, GArbitrary a ga some, ga ~ Rep a)
215374 => Gen a
216−genericArbitrary = G.to <$> gArbitrary @a
375+genericArbitrary = G.to <$> gArbitrary (Proxy :: Proxy a)