A twist on this Gist: https://gist.github.com/ocharles/556b35e3d16565cab457. Retrying actions with delays using the iterative monad transformer. Requires free >= 4.10.0.1.

retries.lhs

> import Safe (readMay)
> import Control.Monad
> import Control.Monad.Trans
> import Control.Monad.Trans.Iter (delay,untilJust,IterT,retract,cutoff)
> import Control.Concurrent (threadDelay)

This is an action that may fail:

> maybeReadInteger :: IO (Maybe Integer)
> maybeReadInteger = liftM readMay (putStr ">" >> getLine)

This is an infinite sequece of "delays", of two seconds each:

> delays :: IterT IO a
> delays = forever (delay (lift (threadDelay (2*10^6))))
 
This tries 4 times to read an integer:
 
> retryIntegerRead :: IO (Maybe Integer)
> retryIntegerRead = 
>     (retract . cutoff 4) (delays `mplus` untilJust maybeReadInteger)

`untilJust` turns `maybeReadInteger` into a computation that keeps retrying until it succeeds.

We "sum" that computation with the `delays` one. `mplus` for `IterT` 
makes the two computations "race" each other, and returns the value of the one that finishes earlier.

Since we don't want to wait forever in case of repeated failures, we establish a cutoff of 4 and
then retract.