{-# LANGUAGE MultiParamTypeClasses, GeneralizedNewtypeDeriving #-} module Test.QuickCheck.Modifiers ( -- ** Type-level modifiers for changing generator behavior Blind(..) , Fixed(..) , OrderedList(..) , NonEmptyList(..) , Positive(..) , NonZero(..) , NonNegative(..) , Smart(..) , Shrink2(..) , Shrinking(..) , ShrinkState(..) ) where -------------------------------------------------------------------------- -- imports import Test.QuickCheck.Gen import Test.QuickCheck.Arbitrary import Data.List ( sort ) -------------------------------------------------------------------------- -- ** arbitrary modifiers -- These datatypes are mainly here to *pattern match* on in properties. -- This is a stylistic alternative to using explicit quantification. -- In other words, they should not be replaced by type synonyms, and their -- constructors should be exported. -- Examples: {- prop_TakeDropWhile (Blind p) (xs :: [A]) = -- because functions cannot be shown takeWhile p xs ++ dropWhile p xs == xs prop_TakeDrop (NonNegative n) (xs :: [A]) = -- (BTW, also works for negative n) take n xs ++ drop n xs == xs prop_Cycle (NonNegative n) (NonEmpty (xs :: [A])) = -- cycle does not work for empty lists take n (cycle xs) == take n (xs ++ cycle xs) prop_Sort (Ordered (xs :: [OrdA])) = -- instead of "forAll orderedList" sort xs == xs -} -------------------------------------------------------------------------- -- | @Blind x@: as x, but x does not have to be in the 'Show' class. newtype Blind a = Blind a deriving ( Eq, Ord, Num, Integral, Real, Enum ) instance Show (Blind a) where show _ = "(*)" instance Arbitrary a => Arbitrary (Blind a) where arbitrary = Blind `fmap` arbitrary shrink (Blind x) = [ Blind x' | x' <- shrink x ] -------------------------------------------------------------------------- -- | @Fixed x@: as x, but will not be shrunk. newtype Fixed a = Fixed a deriving ( Eq, Ord, Num, Integral, Real, Enum, Show, Read ) instance Arbitrary a => Arbitrary (Fixed a) where arbitrary = Fixed `fmap` arbitrary -- no shrink function -------------------------------------------------------------------------- -- | @Ordered xs@: guarantees that xs is ordered. newtype OrderedList a = Ordered [a] deriving ( Eq, Ord, Show, Read ) instance (Ord a, Arbitrary a) => Arbitrary (OrderedList a) where arbitrary = Ordered `fmap` orderedList shrink (Ordered xs) = [ Ordered xs' | xs' <- shrink xs , sort xs' == xs' ] -------------------------------------------------------------------------- -- | @NonEmpty xs@: guarantees that xs is non-empty. newtype NonEmptyList a = NonEmpty [a] deriving ( Eq, Ord, Show, Read ) instance Arbitrary a => Arbitrary (NonEmptyList a) where arbitrary = NonEmpty `fmap` (arbitrary `suchThat` (not . null)) shrink (NonEmpty xs) = [ NonEmpty xs' | xs' <- shrink xs , not (null xs') ] -------------------------------------------------------------------------- -- | @Positive x@: guarantees that @x \> 0@. newtype Positive a = Positive a deriving ( Eq, Ord, Num, Integral, Real, Enum, Show, Read ) instance (Num a, Ord a, Arbitrary a) => Arbitrary (Positive a) where arbitrary = (Positive . abs) `fmap` (arbitrary `suchThat` (/= 0)) shrink (Positive x) = [ Positive x' | x' <- shrink x , x' > 0 ] -------------------------------------------------------------------------- -- | @NonZero x@: guarantees that @x \/= 0@. newtype NonZero a = NonZero a deriving ( Eq, Ord, Num, Integral, Real, Enum, Show, Read ) instance (Num a, Ord a, Arbitrary a) => Arbitrary (NonZero a) where arbitrary = fmap NonZero $ arbitrary `suchThat` (/= 0) shrink (NonZero x) = [ NonZero x' | x' <- shrink x, x' /= 0 ] -------------------------------------------------------------------------- -- | @NonNegative x@: guarantees that @x \>= 0@. newtype NonNegative a = NonNegative a deriving ( Eq, Ord, Num, Integral, Real, Enum, Show, Read ) instance (Num a, Ord a, Arbitrary a) => Arbitrary (NonNegative a) where arbitrary = frequency -- why is this distrbution like this? [ (5, (NonNegative . abs) `fmap` arbitrary) , (1, return 0) ] shrink (NonNegative x) = [ NonNegative x' | x' <- shrink x , x' >= 0 ] -------------------------------------------------------------------------- -- | @Shrink2 x@: allows 2 shrinking steps at the same time when shrinking x newtype Shrink2 a = Shrink2 a deriving ( Eq, Ord, Num, Integral, Real, Enum, Show, Read ) instance Arbitrary a => Arbitrary (Shrink2 a) where arbitrary = Shrink2 `fmap` arbitrary shrink (Shrink2 x) = [ Shrink2 y | y <- shrink_x ] ++ [ Shrink2 z | y <- shrink_x , z <- shrink y ] where shrink_x = shrink x -------------------------------------------------------------------------- -- | @Smart _ x@: tries a different order when shrinking. data Smart a = Smart Int a instance Show a => Show (Smart a) where showsPrec n (Smart _ x) = showsPrec n x instance Arbitrary a => Arbitrary (Smart a) where arbitrary = do x <- arbitrary return (Smart 0 x) shrink (Smart i x) = take i' ys `ilv` drop i' ys where ys = [ Smart i y | (i,y) <- [0..] `zip` shrink x ] i' = 0 `max` (i-2) [] `ilv` bs = bs as `ilv` [] = as (a:as) `ilv` (b:bs) = a : b : (as `ilv` bs) {- shrink (Smart i x) = part0 ++ part2 ++ part1 where ys = [ Smart i y | (i,y) <- [0..] `zip` shrink x ] i' = 0 `max` (i-2) k = i `div` 10 part0 = take k ys part1 = take (i'-k) (drop k ys) part2 = drop i' ys -} -- drop a (drop b xs) == drop (a+b) xs | a,b >= 0 -- take a (take b xs) == take (a `min` b) xs -- take a xs ++ drop a xs == xs -- take k ys ++ take (i'-k) (drop k ys) ++ drop i' ys -- == take k ys ++ take (i'-k) (drop k ys) ++ drop (i'-k) (drop k ys) -- == take k ys ++ take (i'-k) (drop k ys) ++ drop (i'-k) (drop k ys) -- == take k ys ++ drop k ys -- == ys -------------------------------------------------------------------------- -- | @Shrinking _ x@: allows for maintaining a state during shrinking. data Shrinking s a = Shrinking s a class ShrinkState s a where shrinkInit :: a -> s shrinkState :: a -> s -> [(a,s)] instance Show a => Show (Shrinking s a) where showsPrec n (Shrinking _ x) = showsPrec n x instance (Arbitrary a, ShrinkState s a) => Arbitrary (Shrinking s a) where arbitrary = do x <- arbitrary return (Shrinking (shrinkInit x) x) shrink (Shrinking s x) = [ Shrinking s' x' | (x',s') <- shrinkState x s ] -------------------------------------------------------------------------- -- the end.