2009/2/14 Peter Verswyvelen <bugfact@gmail.com>

If you have two streams of time/value pairs - using MVars as write-once sampling variables - and both streams are fed from another thread (e.g. timers firing), and you want to merge these two streams into a single stream with monotonic time stamps, then you want to be able to check if at time t an occurrence exists in a stream.

What you want to do isn't actually achievable on multi-processor machines without some form of mutual exclusion. Time on different cores does not progress monotonically, and you'll pay an enormous performance penalty to do what you want to do (the nature of which is somewhat unclear).