Default module header `module Main where`

[Adam Bergmark]

GHCIs current behavior seems inconsistent with this, why is foo accessible
and why don't I get an unused warning like i do if i have an explicit
`module Main (main) where`?

```
$ cat Main.hs
main :: IO ()
main = pure ()

foo :: Int
foo = 1

$ ghci Main.hs -Wall
GHCi, version 8.0.2: http://www.haskell.org/ghc/  :? for help
Loaded GHCi configuration from /Users/adam.bergmark/.ghci
[1 of 1] Compiling Main             ( Main.hs, interpreted )
Ok, modules loaded: Main.

λ foo
1
```

On Tue, 16 May 2017 at 19:00 José Manuel Calderón Trilla <jmct at jmct.cc>
wrote:

> Agreed, this sounds sensible.
>
> Can anyone think of any unintended consequences?
>
> -Jose
>
> On Tue, May 16, 2017, at 09:50 AM, Iavor Diatchki wrote:
>
> That seems fairly reasonable to me.
>
> -Iavor
>
> On Tue, May 16, 2017 at 7:18 AM, Joachim Breitner <
> mail at joachim-breitner.de> wrote:
>
> Hi,
>
> a very small proposal to be considered for Haskell':
>
> Currently, the report states
>
>     An abbreviated form of module, consisting only of the module body,
>     is permitted. If this is used, the header is assumed to be ‘module
>     Main(main) where’.
>
> I propose to change that to
>
>     An abbreviated form of module, consisting only of the module body,
>     is permitted. If this is used, the header is assumed to be ‘module
>     Main where’.
>
> The rationale is that a main-less main module is still useful, e.g.
> when you are working a lot in GHCi, and offload a few extensions to a
> separate file. Currently, tools like hdevtools will complain about a
> missing main function when editing such a file.
>
> It would also work better with GHC’s -main-is flag, and avoid problems
> like the one described in https://ghc.haskell.org/trac/ghc/ticket/13704
>
>
> I don’t see any downsides. When compiling to a binary, implementations
> are still able to detect that a Main module is not imported by any
> other module and only the main function is used, and optimize as if
> only main were exported.
>
> Greetings,
> Joachim
>
>
>
> --
> Joachim “nomeata” Breitner
>   mail at joachim-breitner.de • https://www.joachim-breitner.de/
>   XMPP: nomeata at joachim-breitner.de • OpenPGP-Key: 0xF0FBF51F
>   Debian Developer: nomeata at debian.org
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