Need assistance with parameterized sequence

SystemVerilog
, ,
1

[A] I am trying to code a generic sequence : ( seq1[*count] ##N seq2 ) where N is passed while asserting the sequence.

bit clk , a , b , c , d;  
int dyn ;
  
 always #5 clk = !clk;
  
 sequence my_seq(seq,count,N,seq3);   
   ((count == 0)  ##0 seq[*0] ##((N > 0) ? N:0) seq3) // Need help with this sequence
  or ((count > 0) ##0 <some_sequence>) ;
  endsequence

  asp:assert property( @(posedge clk) my_seq( a ##1 b,dyn,2,c ##0 d) ) $display("T:%0t Pass",$time); else  $display("T:%0t Fails",$time);
                  
  initial begin   
        dyn = 0 ;
    #04; c = 1 ; d = 1;
    #12; $finish();
  end

On 2 tools I run into a compilation error ::

Error-[SVA-SEQPROPEMPTYMATCH] Invalid sequence as property
A sequence that is used as property must be non-degenerate and admit no empty match.

xmsim: *E,ABVNDG: Degenerate sequence used in assertion ‘asp’. Assertion will not be checked

I am aware that ( empty_seq ## 0 seq ) is illegal however such a sequence doesn’t exist based on actual sequence argument ( N == 2 )

My expectation was that based on the arguments to my_seq the sequence expression would be

seq[*0] ##(2) seq3 ;  // same as ##1 seq3

I expected pass at t:15 units

[B] My intention is the generic sequence to behave as

//  For  N > 0 and ( count == 0 ) ::
sequence my_seq(seq,count,N,seq3);   
    (count == 0) ##0 seq[*0] ##N  seq3 ; //  Equivalent to ##(N-1) seq3
 endsequence

//  For  N <= 0 and ( count == 0 ) ::
sequence my_seq(seq,count,N,seq3);   
    (count == 0) ##0 seq[*0] ##N  seq3 ; //  Should observe compilation error
 endsequence

Any suggestions are welcome

[C] Following assertion is illegal since it’s a degenerate sequence

prop1:assert property( @(posedge clk) empty_seq ## 0 seq ) ;  // Illegal

      If I were to add an expression after the clocking event 

prop2:assert property( @(posedge clk) (some_variable == 0) ##0 empty_seq ## 0 seq  );

In this latter case when (some_variable == 0) we should observe compilation error
but when (some_variable != 0 ) , shouldn’t the fail action block execute ?
I expected that when (some_variable != 0) the sequence ( empty_seq ## 0 seq ) won’t be evaluated ,
hence there would be No compilation error ( for the degenerate sequence )

2

To answer my own questions

[A] Due to left to right associativity : ( count == 0 ) ## 0 seq[*0] is degenerate and hence illegal.
[B] Solution is to add a parenthesis

(count == 0) ##0 ( seq[*0] ##( (N > 0) ? N : 0 ) seq3 );

[C] Due to left to right associativity : seq1 ##0 empty_seq ##0 seq2 is degenerate
and hence illegal irrespective of whether ‘seq1’ i.e (some_variable == 0) matches or not