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haskell - 有没有办法在 Haskell QuickCheck 中生成用于测试的值？

问题描述

我有 2 种数据类型用于表示一元系统中的自然数

data Valoare_Unar = Unu deriving(Show);
data Numar_Unar = Invalid | Unar [Valoare_Unar] deriving(Show);

我有这些函数可以将此数字从整数转换为我的数据类型，反之亦然。

convert :: Unar.Numar_Unar -> Integer
convert Unar.Invalid = (-1)
convert (Unar.Unar xs)
    | null xs   = 0
    | otherwise = 1 + convert (Unar.Unar (tail xs))

convert' :: Integer -> Unar.Numar_Unar
convert' (-1) = Unar.Invalid
convert' x = fromInteger x :: Unar.Numar_Unar

我想测试一下(convert' (convert _)) == _，我有 prop_check xs = Utils.convert' (Utils.convert xs) == xs where types = xs::Unar.Numar_Unar。

我已经创建了任意数据类型的实例，但是我在弄清楚我应该如何为“Unar”构造函数生成值时遇到了问题。

instance Arbitrary Valoare_Unar where
        arbitrary = elements [Unu]

instance Arbitrary Numar_Unar where
    arbitrary = elements [Invalid, Unar []]

使用QC.verboseCheck prop_check我注意到唯一的测试值是“无效”和“Unar []”。

我的问题是：如何生成像 "Unar[Unu] ; Unar[Unu,Unu,Unu] ; ... ; Unar [Unu,..,Unu]" 这样的值进行测试？

编辑：实例 Num Numar_Unar

instance Num Numar_Unar where
    (+) (Unar xs) (Unar ys)
        | null ys   = (Unar xs)
        | otherwise = (+) (Unar (xs ++ [head ys])) (Unar (tail ys))
    (+) _ _ = Invalid
    (-) (Unar xs) (Unar ys)
        | length xs < length ys = Invalid
        | null ys               = Unar xs
        | xs == ys              = Unar []
        | otherwise             = (-) (Unar (tail xs)) (Unar (tail ys))
    (-) _ _ = Invalid
    (*) (Unar xs) (Unar ys)
        | null ys   = Unar []
        | otherwise = (+) (Unar xs) ((*) (Unar xs) (Unar (tail ys)))
    (*) _ _ = Invalid
    abs (Unar xs)   = Unar xs
    abs Invalid     = Invalid

    signum (Unar xs)
        | null xs   = Unar []
        | otherwise = Unar [Unu]
    signum Invalid  = Invalid
    fromInteger x 
        | x < 0     = Invalid
        | x == 0    = Unar []
        | otherwise = (+) (Unar [Unu]) (fromInteger (x-1))

标签： haskellquickcheck

解决方案

arbitrary = elements [Invalid, Unar []]意思是“当我arbitrary在这种类型上运行时，总是给我Invalid或Unar []”。一个合适的Arbitrary实例如下所示：

instance Arbitrary Numar_Unar where
    arbitrary = frequency [(1, return Invalid), (3, Unar <$> arbitrary)]

这将使arbitrary生成Invalid1/4 的时间和Unar3/4 的时间。当它生成时Unar，它会调用类型arbitrary来[Valoare_Unar]获取一个包含随机数量元素的列表，而不是总是没有。您还应该考虑向shrink该类添加一个方法，如下所示：

    shrink Invalid = []
    shrink (Unar []) = [Invalid]
    shrink (Unar (Unu:xs)) = [Invalid, Unar [], Unar xs]

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