7
在代碼中定義的函數,有一個奇怪的「模式匹配」 (cradleRootDir -> projdir)
模式匹配在Haskell
我想這是爲了應用功能內嵌並綁定結果的名稱projdir
。
該構造的名稱是什麼?
withGhcModEnv' :: (IOish m, GmOut m) => (FilePath -> (Cradle -> m a) -> m a) -> FilePath -> Options -> ((GhcModEnv, GhcModLog) -> m a) -> m a
withGhcModEnv' withCradle dir opts f =
withCradle dir $ \crdl ->
withCradleRootDir crdl $
f (GhcModEnv opts crdl, undefined)
where
withCradleRootDir (cradleRootDir -> projdir) a = do
cdir <- liftIO $ getCurrentDirectory
eq <- liftIO $ pathsEqual projdir cdir
if not eq
then throw $ GMEWrongWorkingDirectory projdir cdir
else a
data Cradle = Cradle {
cradleCurrentDir :: FilePath
, cradleRootDir :: FilePath
, cradleCabalFile :: Maybe FilePath
, cradlePkgDbStack :: [GhcPkgDb]
} deriving (Eq, Show)
這是一個視圖模式。查看[這個問題](http://stackoverflow.com/q/20766841/2751851)瞭解一些有趣的例子。 – duplode