相关疑难解决方法(0)

在我最近的这个答案中,我碰巧打开了这个老板栗(这个程序太旧了,其中一半是莱布尼兹在十七世纪写的,七十年代由我父亲在电脑上写的).我会省去现代的位以节省空间.

class Differentiable f where
  type D f :: * -> *

newtype K a     x  = K a
newtype I       x  = I x
data (f :+: g)  x  = L (f x)
                   | R (g x)
data (f :*: g)  x  = f x :&: g x

instance Differentiable (K a) where
  type D (K a) = K Void
instance Differentiable I where
  type D I = K ()
instance (Differentiable f, Differentiable g) => Differentiable …