Fwd: [Haskell-cafe] Fuzzy time deltas

[Alberto G. Corona]

Michael,

The package Workflow has persistent timeouts (can wait for years and
restart on system failure if embedded in the workflow monad, although
it can run in the IO monad, with no recovery). They are composable
with any action in the STM monad with orElse:


   flag <- getTimeoutFlag $  5*24*60 * 60    -- wait exactly 5 days. even
                                                              -- if the
program restart
   ap <- step  .  atomically $  readSomewhere >> return False
                             `orElse`  waitUntilSTM flag  >> return True

   case ap of
                   False -> print "something received"
                   True  -> print "timeout"



step"  lift it from the IO to the workflow monad, and gives it
persistence and recovery.

without "step", it runs in the IO monad (No recovery on system failure):

flag <- transientTimeout $  5*24*60 * 60    -- wait 5 days, timeout
                                                             -- restarts in
case of  failure
ap <-  atomically $  readSomewhere >> return False
                `orElse`  waitUntilSTM flag  >> return True
case ap of
                  False -> print "something received"
                  True  -> print "timeout"

------
transientTimeout t= do
  flag <- atomically $ newTVar False
  forkIO $ threadDelay(t * 1000000) >> atomically (writeTVar flag True)
              >> myThreadId >>= killThread
  return flag


2010/10/14 Michael Snoyman <michael at snoyman.com>:
> Hey all,
>
> Is there a library that supports fuzzy time deltas? For example, given
> two UTCTimes (or something like that) it could produce:
>
> 43 seconds
> 13 minutes
> 17 hours
> 4 days
> 8 months
>
> I want to use it for the news feature on Haskellers. It's not that
> hard to write, just wondering if it's already been done.
>
> Michael
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