{-# 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 j y | (j,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.