在haskell代码

Question

我遇到了以下代码：

data Nested a = a :<: (Nested [a]) | Epsilon

mylength Epsilon    = 0
mylength (_ :<: xs) = 1 + mylength xs

a :<: (Nested [a])是什么意思？我不理解这些代码（特别是:<:）

Answer 1

:<:是一个数据构造函数，如Just。唯一的区别是它是中缀，因为它是象征性的。中缀数据构造函数必须以:开头。

您可以将上述内容重写为：

data Nested a = Nest a (Nested [a]) | Epsilon

mylength Epsilon    = 0
mylength (Nest _ xs) = 1 + mylength xs