我该如何把它变成二传手？

Question

setOwner :: File -> User -> File 
setOwner f o = f & ownerID .~ (o ^. User.uid) 

如何将此变为Setter？

我不能使它成为镜头，因为getUser :: UserID -> IO User是一个不纯的功能。

Answer 1

我刚刚意识到我以前的答案是错误的。哎呦！

在这里你去：

ownerS :: Setter File File() User 
ownerS = sets (\f file -> setOwner file (f()))