如何构建具有可选依赖项的Haskell程序？

{-# LANGUAGE CPP #-}

#ifdef OPTIONAL_DEPENDENCY
import OptionalDependency.Module (someFunction)
#else
someFunction :: Int -> Int
someFunction x = x + 1
#endif

ghc -DOPTIONAL_DEPENDENCY Main.hs

optionalDependencies:
  enableOptionalDependency: true

import Data.Yaml (decodeFileEither)
import qualified Data.ByteString.Lazy as BL
import Control.Monad (when)

data Config = Config { enableOptionalDependency :: Bool } deriving (Show, Generic)
instance FromJSON Config

main :: IO ()
main = do
  config <- decodeFileEither "config.yaml" >>= either fail return
  when (enableOptionalDependency config) $ do
    -- 导入和使用可选依赖项
    import OptionalDependency.Module (someFunction)
    print $ someFunction 42

executable my-exe
  build-depends: base >= 4.14 && < 5
               , optionalDependencies:
                   my-optional-dep >= 1.0 && < 2.0

  if flag(optional-dep)
    build-depends: my-optional-dep >= 1.0 && < 2.0

cabal build --enable-flag=optional-dep