haskell - 缺少随附的绑定(bind) - 这是什么意思？这个怎么运作？

Question

我在 LYAH 练习。

phoneBook.hs 文件包含以下代码:

phoneBook :: [(String, String)]

在尝试编译上述代码时，出现以下错误:

*Main> :load "/home/optimight/phoneBook.hs" [1 of 1] Compiling Main ( /home/optimight/phoneBook.hs, interpreted )

/home/optimight/phoneBook.hs:1:1: The type signature for `phoneBook' lacks an accompanying binding Failed, modules loaded: none.

在 brano 的回答和对该答案的后续评论之后添加的问题:我们如何为上述类型签名提供实现？

如果我添加这个:

type phoneBook = [(String, String)]

我收到以下错误:

Prelude> :load "/home/optimight/phoneBook.hs" [1 of 1] Compiling Main ( /home/optimight/phoneBook.hs, interpreted )

/home/optimight/phoneBook.hs:2:6: Malformed head of type or class declaration: phoneBook Failed, modules loaded: none

Answer 1

您需要为电话簿提供一个实现。
phoneBook :: [(String, String)] 只是签名。