我拿着一套用户、群体以及用户和群体之间的绘图。 我有各种功能操纵这些设备,但不能增加一个用户配对器;对一个没有用户的用户进行组群测绘,也不能排除一个仍然有用户作为成员的群体等。
因此,我基本上希望这些职能屈服于呼吁者必须明确处理的“例外”。
我首先想回到这样的东西:
data Return r e = Success r | Exception e
如果打电话者没有与<>Exception<>t/code>匹配,他们希望能收到编辑警告,或者至少在存在问题时有明显的操作错误。
这是最佳办法,是否有事先包装的解决办法? 请注意,我需要在纯粹的法典中,而不是在IO Monad中 throw取“例外”。
是的,这是一个好的做法,在标准图书馆:Return r e与 e r。 您甚至可以写像你那样的代码,如在<代码>IO上使用例外情况(即不必在每一步与格式匹配之间明确处理错误):<代码>Monad上播放错误的表格,就像<代码>be May monad那样(但在出现错误时,附加
data MyError
= Oops String
| VeryBadError Int Int
mightFail :: T -> Either MyError Int
mightFail a = ...
foo :: T -> T -> Int -> Either MyError Int
foo a b c = do
x <- mightFail a
y <- mightFail b
if x == y
then throwError (VeryBadError x y)
else return (x + y + c)
如果mightFail a or mightFail b Return Left someError,则 a b也将自动传播这些错误。 (Here,throwError 使用Control. Monad.Error的职能,仅是书面的冰箱;还有liver Error来追捕这些例外情况。
<代码>Return r e, 您描述的正是标准类型。
data Either a b = Left a | Right b
You might want to use the so called "error monad" (a more suitable name is "exception monad") of the mtl package. (Alternatively, there s ExceptionT in the monadLib package if you don t want to use mtl.) This allows you to do error handling in pure code by invoking throwError and catchError.
Here you can find an example that shows how to use it.
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