retry-0.6: Retry combinators for monadic actions that may fail

This package exposes combinators that can wrap arbitrary monadic actions. They run the action and potentially retry running it with some configurable delay for a configurable number of times. The purpose is to make it easier to work with IO and especially network IO actions that often experience temporary failure and warrant retrying of the original action. For example, a database query may time out for a while, in which case we should hang back for a bit and retry the query instead of simply raising an exception.