[Haskell-cafe] Implicit Multi Threading in Switch Case

Richard A. O'Keefe ok at cs.otago.ac.nz
Tue Jun 20 22:23:39 UTC 2017

As I understand it, the original poster wanted the arguments
to be evaluated *concurrently* and to catch whichever of them
finished first.  (OK, define "finished" to be "evaluated to
WHNF".)  Years ago people used to discuss the question of
whether it was possible to define

   or True _ = True
   or _ True = True
   or False x = x
   or x False = x

symmetrically, so that if *either* argument returned True,
the result True would be delivered, even if the other
argument diverged.  As I recall it, the answer was "NO",
but I don't recall the proof.

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