为什么在没有额外缩进的情况下,换行符匹配的语法错误,以及推荐的样式是什么？

Question

我刚发现这个

foo = case ((), ()) of
       ( ()
       , () ) -> ()

失败了

/tmp/wtmpf-file11080.hs:3:8:
    parse error (possibly incorrect indentation or mismatched brackets)

这可以通过缩进模式的第二行来实现

foo = case ((), ()) of
       ( ()
        , () ) -> ()

但这感觉与我平常的风格不一致,特别是在

bar = case ( some lengthy :: Complicated typed expression
           , another also lengthy :: Expression with (Other types) ) of
       ( Complicated (Pattern match) to (unwrap)
       , Expression that's (Again not so short) ) -> the Rest of my Code

如何重写/格式化以使其看起来最一致？

Answer 1

通过缩进规则,代码

foo = case ((), ()) of
       ( ()
       , () ) -> ()

很沮丧

foo = case ((), ()) of
       { ( ()
       ; , () ) -> ()
       }

这是一个case有两个分支,第一个是语法错误.

我建议使用以下样式:

foo = case ((), ()) of
       (( ()
        , () )) -> ()

甚至(不是非常优雅)

foo = case ((), ()) of
       _@( ()
         , () ) -> ()