[Haskell-cafe] Dealing with GHC 7.10 prelude imports

[Michal Antkiewicz]

Hi,

the only problem with the "import Prelude" trick is that it does not help
when you explicitly list what you import. For example, in one of my files I
had:

import Control.Applicative ((<$>))

which will still result in a warning. Simply change it to

import Control.Applicative
import Prelude

However, sometimes there are conflicting names due to reexports. For
example, forM is both in Data.Traversable and Control.Monad. In such a
case, use "hiding" for one of them.

Also change

import <module> (<f>)

to

import <module> hiding (<everything except f>)

if you want to avoid CPP at all cost.

I too went through a few cycles 7.8.4 <-> 7.10.1 trying to make the code
warning free on both (I don't use Travis but having minghc on Windows or
using HVR's PPA on Ubuntu helps a lot).

Michal

On Sun, Apr 12, 2015 at 3:45 PM, Brendan Hay <brendan.g.hay at gmail.com>
wrote:

> Thanks for the tips!
>
> On 12 April 2015 at 12:37, Benno Fünfstück <benno.fuenfstueck at gmail.com>
> wrote:
>
>> > I've run into a couple of cases when attempting to support multiple GHC
>> versions in my libraries (7.6.3 -> 7.10) where I've repeatedly made
>> mistakes due to being warned about unused imports for various modules that
>> are now part of the Prelude such as Data.Monoid, Data.Foldable, etc. which
>> I subsequently remove either manually or via editor automation sufficiently
>> indistinguishable from magic.
>>
>> A trick is to import Prelude at the very end, like:
>>
>> import Control.Applicative
>> import Data.Monoid
>> ...
>> import Prelude
>>
>> Since the unused import check is done from top to bottom, and you almost
>> always use *something* from the Prelude, this will suppress the warning.
>>
>> There are some problems with qualified/explicit import lists if I recall
>> correctly though. But it works for me most of the time.
>>
>> Regards,
>> Benno
>>
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>
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