循环类型同义词声明

我想用下面的代码尝试Haskell type和data

type Program a = Maybe a -> (Operation a, Maybe Program a)
data Operation a = Read a | Write a

Program遵循延续传球风格（CPS）， Nothing表示终止。 a可以用Int或其他东西实例化。

但是，GHC抱怨说：

main.hs:1:1:
    Cycle in type synonym declarations:
      main.hs:1:1-58: type Program a =
                          Maybe a -> (Operation a, Maybe Program a)

我是Haskell的新手，所以我不明白为什么这是不允许的。 我如何在Haskell中表达这种类型？

---

这里有两个问题：

它应该是Maybe (Program a) ，而不是Maybe Program a

类型同义词不能递归

工作版本将是：

newtype Program a = Program { runProgram :: Maybe a -> (Operation a, Maybe (Program a)) }
data Operation a = Read a | Write a

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