haskell - Haskell：多个文件的酸性状态？

Question

我有这样的文件结构：

--- Database.hs ---
data Database = ...
...

--- User.hs ---
import Database
addUser :: Update Database ()
...

--- Post.hs
import Database
addPost :: Update Database ()
...

问题是我需要同时调用makeAcidic ''Database [...]它们User.hs并使Post.hs它们的函数变酸，但makeAcidic同时生成IsAcidic实例，Database因此 GHC 抱怨重复的实例声明。

Answer 1

好的，所以我想通了。只需将定义与 Template Haskell 分开：

--- Database/Types.hs ---
data Database = ...
...

--- Database.hs ---
import Database.Types
import User
import Post
makeAcidic ''Database [addUser, addPost]

--- User.hs ---
import Database.Types
addUser :: Update Database ()
...

--- Post.hs ---
import Database.Types
addPost :: Update Database ()
...