安装scion浏览器时出错

Question

我在尝试安装scion浏览器包时收到以下错误，如下所示：

% cabal install scion-browser-0.2.9
<snipped>
[23 of 23] Compiling Main             ( src/Main.hs, dist/build/scion-browser/scion-browser-tmp/Main.o )
src/Main.hs:31:24:
    No instance for (MonadException BrowserM)
      arising from a use of `getInputLine'
    Possible fix:
      add an instance declaration for (MonadException BrowserM)
    In a stmt of a 'do' block: maybeLine <- getInputLine ""
    In the expression:
      do { maybeLine <- getInputLine "";
           case maybeLine of {
             Nothing -> return ()
             Just line -> do { ... } } }
    In an equation for `loop':
        loop
          = do { maybeLine <- getInputLine "";
                 case maybeLine of {
                   Nothing -> return ()
                   Just line -> ... } }
cabal: Error: some packages failed to install:
scion-browser-0.2.9 failed during the building phase. The exception was:
ExitFailure 1

知道怎么解决这个问题吗？

谢谢。

Answer 1

问题是haskeline-0.7.0.0更改了所使用的StateT类型。在haskeline < 0.7中，它使用了来自mtl的Control.Monad.State模块，在0.7.0.0版本中，haskeline放弃了对mtl的依赖，直接使用transformers包的StateT monad transformer。这本身就不是问题，因为mtl现在只是transformers的包装。然而，haskeline使用的模块是Control.Monad.Trans.State.Strict，而来自mtl的Control.Monad.State封装Control.Monad.Trans.State.Lazy。因此

instance MonadException m => MonadException (StateT s m) where
    controlIO f = StateT $ s -> controlIO $ (RunIO run) -> let
                    run' = RunIO (fmap (StateT . const) . run . flip runStateT s)
                    in fmap (flip runStateT s) $ f run'

来自CCD_ 14的CCD_。

简单的解决方案是将haskeline约束到早期版本

cabal install --constraint="haskeline < 0.7" scion-browser

另一个修复方法是将scion-browser源中的导入更改为Control.Monad.State.Strict，使其使用haskeline-0.7.0.0构建。