[英]How to write a “retryForever” function in Haskell using exception handling?
I'd like to create a function that can recover from as many errors as is reasonable, and try again. 我想创建一个可以从合理的错误中恢复的函数,然后再试一次。 Of course, meaningful handling of errors is covered in other parts of the program - this is a last ditch effort to keep things running.
当然,程序的其他部分也包含有意义的错误处理 - 这是保持运行的最后努力。 So I wrote this:
所以我写了这个:
retryForever prog = catchAny prog progRetry
where
progRetry :: SomeException -> m a
progRetry ex = do
putStrLn $ pack $ show ex
threadDelay 4000
prog
Then I wrap my main IO action in retryForever
: 然后我将我的主IO动作包装在
retryForever
:
main :: IO ()
main = retryForever $ do
logger <- newLogger
-- ...
In another part of my program (likely a different green thread), I test this with: 在我的程序的另一部分(可能是一个不同的绿色线程),我用以下方法测试:
error "this is a TEST ERROR"
Resulting in: 导致:
: this is a TEST ERROR
CallStack (from HasCallStack):
error, called at XXXX
(and the program dies instead of continuing on) (程序会死而不是继续)
Note that I'm using classy-prelude, for the cases where that may matter, eg catchAny
doesn't handle asynchronous exceptions in there, which may well be the issue here. 请注意,我正在使用classy-prelude,对于可能很重要的情况,例如
catchAny
不会处理那里的异步异常,这可能是这里的问题。
When the program failed, you should run the program prog
again, but wrapped in retryForever
such that if it fails again, you thus keep trying: 当程序失败时,你应该再次运行程序
prog
,但是包装在retryForever
这样如果它再次失败,你就会继续尝试:
import Control.Monad.Catch(catchAll)
retryForever :: IO a -> IO a
retryForever prog = catchAll prog retry
where retry ex = do
putStrLn $ pack $ show ex
threadDelay 4000
retryForever prog
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