On Wed, 2014-12-24 at 09:49 -0500, Doug Burke wrote:

I'm trying out the ghc 7.10 RC and am seeing lots of warnings about Monoid and some symbols from Control.Applicative - e.g.

The import of ‘Data.Monoid’ is redundant except perhaps to import instances from ‘Data.Monoid’ To import instances alone, use: import Data.Monoid()

For now I'm wrapping the import with some CPP so that it will still compile with older ghc versions (and a probably-pointless attempt to be non-ghc-specific, since I have never tested my code with other compilers):

#if (!defined(__GLASGOW_HASKELL__)) || (__GLASGOW_HASKELL__ < 710) import Control.Applicative (Applicative(pure), (<$>), (<*>)) import Data.Monoid (Monoid(..)) #else import Control.Applicative ((<$>)) #endif

Is this the best way? Am I missing something really obvious?

I don't even have plans to adopt ghc-7.10 yet, so I don't know the best way to handle that. But for similar issue I usually avoid CPP at use side. It is better to make compatibility layer that hides all the CPP. I successfully used that approach to handle `catch` removal from `Prelude`. I have `Prelude.hs` visible to ghc with the next contents:

{-# LANGUAGE PackageImports #-} {-# LANGUAGE CPP #-}

module Prelude ( module P ) where

#if MIN_VERSION_base(4,6,0) import "base" Prelude as P #else import "base" Prelude as P hiding (catch) #endif

I think the same trick can be used to handle AMP changes. E.g. you can add "Control/Monad.hs" file that reexports `Control.Applicative`. Probably you can avoid CPP altogether if you specify different `hs-source-dirs` for different ghc versions in cabal file. Thanks, Yuras

Thanks, Doug _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe