只需将文件名添加到你的.gitignore文件。例如： $ git ls-files --other --exclude-standard test $ echo test > .gitignore $ git ls-files --other --exclude-standard $ ... 展开详请

模式： import qualified Data.Map as Map -- | takes input and a map, and returns a result and a modified map myFunc :: a -> Map.Map k v -> (r, Map.Map k v) myFunc a m = … -- put your function here -- | run myFunc over a list of inputs, gathering the outputs mapFuncWithMap :: [a] -> Map.Map k v -> ([r], Map.Map k v) mapFuncWithMap as m0 = foldr step ([], m0) as where step a (rs, m) = let (r, m') = myFunc a m in (r:rs, m') -- this starts with an initial map, uses successive versions of the map -- on each iteration, and returns a tuple of the results, and the final map -- | run myFunc over a list of inputs, gathering the outputs mapFunc :: [a] -> [r] mapFunc as = fst $ mapFuncWithMap as Map.empty -- same as above, but starts with an empty map, and ignores the final map ... 展开详请

导出Functor实例总是做显而易见的事情。这通常是很好的，但偶尔会错过机会。例如，假设我写 data Pair a = Pair a a deriving Functor data Digit a = One a | Two a a deriving Functor data Queue a = Empty | Single a | Deep !(Digit a) (Queue (Pair a)) !(Digit a) deriving Functor 这将生成(在ghc 8.2中) instance Functor Queue where fmap ... x <$ Empty = Empty x <$ Single y = Single x x <$ Deep pr m sf = Deep (x <$ pr) (fmap (x <$) m) (x <$ sf) 用手写最后一个例子是可能的： x <$ Deep pr m sf = Deep (x <$ pr) (Pair x x <$ m) (x <$ sf) 可以看到实际的派生代码-ddump-deriv...... 展开详请