RE: black hole detection and concurrency

| I have a good theory on the latter symptom (the "thread killed" | message). Sticking in some traces, as in my appended code, helped me | to see what's going on. It seems to be exactly what you describe -- | the variable v is permanently bound to the exception it "evaluates" | to. Since the right hand True portion of the unamb evaluates more | quickly, the spawned threads are killed and the left hand (the v) | "evaluates" to "thread killed". This is odd (to me). The "permanently bound" stuff applies only to *synchronous* exceptions, which thread-killing is not. Simon M will have more to say when he gets back Simon