问题描述
我正在尝试在Haskell中编写一个模块.它没有main，因为它不是独立程序.
I'm trying to write a module in Haskell. It does not have a main because it's not meant to be a stand-alone program.
我刚开始使用合成词，并且不断报告:
I just started using syntastic, and it is constantly reporting:
The IO action ‘main’ is not defined in module ‘Main’
这可以防止它报告模块中的其他实际错误.如果我尝试通过添加一个虚拟主电源来解决此问题，它将开始抱怨其他所有内容都是已定义但未使用".
This is preventing it from reporting other real errors in my module. If I try to work around this by adding a dummy main, it starts complaining that everything else is "Defined but not used".
我该如何告诉syntastic(以及幕后使用的任何检查器)，应该没有main?
How can I tell syntastic (and whatever checker it's using under the covers) that there isn't supposed to be a main?
推荐答案
使用ghc-mod进行测试(虽然也可以使用hdevtools，但支持合成):
Testing with ghc-mod (which backs syntastic, although hdevtools is possible too):
$ cat test1.hs
f :: Int -> Int
f x = x + 1
$ ghc-mod check test.hs
test1.hs:1:1:The IO action 'main' is not defined in module 'Main'
$ cat test2.hs
module Test where
f :: Int -> Int
f x = x + 1
$ ghc-mod check test.hs
$
因此，您只需在文件中放置一个虚拟模块声明，警告就会消失.
So you can just put a dummy module declaration in your file and the warning will go away.
出现此警告的原因是，默认情况下，在Haskell中，任何未声明的模块都具有名称Main.由于您尚未定义main :: IO ()且模块名称隐式为Main，因此ghc-mod会发出警告.如果您声明它不是Main之外的东西，ghc-mod会认为您只是在导出模块中的所有内容，因为所有内容都是从模块中隐式导出的.
The reason why this warning pops up is because by default in Haskell any undeclared module has the name Main. Since you haven't defined a main :: IO () and the module name is implicitly Main ghc-mod throws a warning. If you declare it to be something other than Main, ghc-mod thinks you're just exporting everything in the module, since everything is implicitly exported from a module.
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