Re: [sv-ac] Mantis item #1591

Hi Dmitry:

I also prefer the uniformity and flexibility of the second
alternative.

I'd like to know what other actual argument lists in the language
do when argument expressions can be omitted (e.g., because there
is a default).  Do you know?

J.H.

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> From: "Korchemny, Dmitry" <dmitry.korchemny@intel.com>
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> Hi all,
> 
> =20
> 
> I was sure I sent this mail three weeks ago, but I cannot find it in the
> reflector somehow. Therefore I am resending it now.
> 
> =20
> 
> Shalom opened a Mantis item #1591:
> 
> =20
> 
> The syntax of $past is described in 17.7.3 and 22.9 as=20
> $past( expression1 [, number_of_ticks] [, expression2] [,
> clocking_event])
> 
> This is not precise as it both implies that the 3rd or 4th argument may
> be present without at least the commas preceding the preceding
> arguments, and also does not show that the actual argument may be
> omitted as long as at least the comma is present (at least for the 2nd
> and 3rd arguments).
> 
> A more precise syntax (though harder to read) is
> 
> $past( expression1 [, [number_of_ticks] [, [ expression2] [,
> clocking_event]]] ) or
> 
> $past( expression1 [, [number_of_ticks] [, [ expression2] [,
> [clocking_event]]]] ) .
> 
> The difference between the two is whether clocking_event may be omitted
> if the last comma is present.
> 
> =20
> 
> =20
> 
> I think that the second alternative is better:
> 
> =20
> 
> $past( expression1 [, [number_of_ticks] [, [ expression2] [,
> [clocking_event]]]] ) .
> 
> 
> 
> because it makes writing scripts easier: there is no need to analyze
> whether the clocking event has been provided or not; the invocation
> string will remain exactly the same.
> 
> =20
> 
> Here is a small Perl example:
> 
> =20
> 
> sub writePastOfSig
> 
> {
> 
>           my $clockEvent =3D shift;
> 
>           print "\$past(sig, 1, 1, $clockEvent)";
> 
> }
> 
> =20
> 
> Both invocations
> 
> =20
> 
> writePastOfSig("@(posedge clk)");
> 
> =20
> 
> and
> 
> =20
> 
> writePastOfSig();
> 
> =20
> 
> will work correctly with this definition. With the first alternative the
> code of writePastOfSig should be more complex.
> 
> =20
> 
> The second alternative is also consistent with the syntax of the general
> function invocation:
> 
> =20
> 
> list_of_arguments ::=3D
> 
> [ expression ] { , [ expression ] } { , . identifier ( [ expression ] )
> }
> 
> | . identifier ( [ expression ] ) { , . identifier ( [ expression ] ) }
> 
> =20
> 
> If so, the definition of other sampled value functions should be
> rewritten accordingly.
> 
> =20
> 
> Thanks,
> 
> Dmitry
> 
> 

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