[sv-ac] Mantis 2476 ($onehot, etc, outside assertions)

Hi guys-I just added this note at http://www.verilog.org/mantis/view.php?id=2476 . Perhaps we can discuss in today's meeting.

We need to decide not just for the functions in the original description, but for all the assertion system functions:
$onehot $onehot0 $isunknown $sampled $rose $fell $stable $changed $past $countones $past_gclk $rose_gclk $fell_gclk $stable_gclk $changed_gclk $future_gclk $rising_gclk $falling_gclk $steady_gclk $changing_gclk

I think the return types are clear in the final 2009 LRM, but the question of their usage outside assertions is left ambiguous. For each of these categories, do we want to enable outside assertions? My instinct is just to enable category #1.
1. Simple booleans ($onehot $onehot0 $isunknown)
2. Sampled value functions ($sampled $rose $fell $stable $changed $past $countones)
3. Global clocking past functions ($past_gclk $rose_gclk $fell_gclk $stable_gclk $changed_gclk)
4. Global clocking future functions ($future_gclk $rising_gclk $falling_gclk $steady_gclk $changing_gclk)

Interestingly, 20.13 seems to have an isolated BNF production "assert_boolean_function" that is not referenced anywhere else in the LRM, leaving it unclear where this can be used, though the implication is that it's restricted to assertions. Should we fix this & Annex A to properly integrate these functions into the grammar as well?

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