Re: [Haskell-cafe] STM rollback?

As far as I understand you can call throwSTM and get desired effect. — Alexander Vershilov

29 нояб. 2020 г., в 00:07, amindfv--- via Haskell-Cafe написал(а):

I'd like to be able to give up on an STM transaction: roll back and don't retry. I've cooked up something with exceptions but it feels a bit icky to use exceptions for something like this - is there a better way?:

data Rollback = Rollback deriving (Show) instance Exception Rollback

rollback :: STM x rollback = throwSTM Rollback

atomicallyWithRollback :: STM x -> IO (Maybe x) atomicallyWithRollback a = (Just <$> atomically a) `catch` (\Rollback -> pure Nothing)

The alternative I've found is something like:

otherWay :: STM x -> IO (Maybe x) otherWay a = atomically $ (Just <$> a) `orElse` pure Nothing

But this turns any "retry" in "a" into a rollback, and I'd like to have the option to do either (retry or rollback).

Thanks, Tom

_______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.