[Haskell-cafe] Dealing with GHC 7.10 prelude imports

[Alan & Kim Zimmerman]

See https://ghc.haskell.org/trac/ghc/wiki/Migration/7.10.

I have just solved one of these by doing

{-# LANGUAGE CPP #-}
#if __GLASGOW_HASKELL__ < 709
import Data.Monoid hiding ((<>))
#endif

Alan


On Sun, Apr 12, 2015 at 9:55 AM, Brendan Hay <brendan.g.hay at gmail.com>
wrote:

> Hi,
>
> 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.
>
> This then results in successful compilation on 7.10 and failure on earlier
> versions of GHC due to missing imports (ie. Data.Monoid (mappend, mempty)),
> which prior to my current workflow of manually building on multiple
> versions of
> GHC before releasing a new version, manifested once or twice only after
> uploading to Hackage.
>
> Now this is all user/workflow error on my part, but I wondered if others
> have
> some kind of trick up their sleeve for avoiding these kind of issues? I
> could
> attempt to tailor the compiler's warning flags appropriately, but it bodes
> ill for
> spotting genuinely unused imports.
>
> Cheers,
> Brendan
>
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