我有一段代码,我已经声明了两种数据类型.我已经自动派生为类型类的成员enum
,但是,我不喜欢它们不是"循环".通过这个,我的意思是召唤succ Sun
应该让我受益Mon
.succ Dec
应该导致Jan
.所以我没有写自己的枚举,而是这样做:
data WeekDay = Mon | Tue | Wed | Thu | Fri | Sat | Sun deriving (Enum, Show, Eq, Bounded) data Month = Jan | Feb | Mar | Apr | May | Jun | July | Aug | Sep | Oct | Nov | Dec deriving (Enum, Show, Eq, Bounded) class Circ a where next :: Enum a => a -> a instance Circ WeekDay where next a = if a == maxBound then minBound else succ a instance Circ Month where -- this is nearly identical to the one above next a = if a == maxBound then minBound else succ a
我的问题是:是否有更整洁,更少冗余的写作方式?换句话说,我写了两个几乎相同的实例,数据类型名称(WeekDay vs. Month)是唯一更改的变量.
class (Enum a, Bounded a, Eq a) => Circ a where next :: a -> a next a = if a == maxBound then minBound else succ a instance Circ WeekDay instance Circ Month
我想以Ingo的答案为基础,指出您实际上根本不需要定义类型类。您可以定义以下函数而无需调用任何其他类型类:
next :: (Eq a, Bounded a, Enum a) => a -> a next a = if a == maxBound then minBound else succ a
现在,您不必instance Circ
为所有类型都声明。