interface Inc;
  method Action inc();
  method Int#(32) count();
endinterface

interface Dec;
  method Action dec();
  method Int#(32) count();
endinterface

module mkA#(Inc b)(Dec);
  Reg#(Int#(32)) r <- mkReg(0);

  rule do_inc(r == 0);
    r <= r + 1;
    b.inc;
  endrule

  method Action dec;
     r <= r - 1;
  endmethod

  method count = r;
endmodule

module mkB#(Dec a)(Inc);
  Reg#(Int#(32)) s <- mkReg(0);

  rule do_dec(s == 1);
    s <= s - 1;
    a.dec;
  endrule

  method Action inc;
    s <= s + 1;
  endmethod

  method count = s;
endmodule

module mkAandB#(Tuple2#(Dec,Inc) ab)(Tuple2#(Dec,Inc));

  Dec a <- mkA(tpl_2(ab));
  Inc b <- mkB(tpl_1(ab));

  return(tuple2(a,b));

endmodule

(* synthesize *)
module sysIncDecFix();

  match {.a, .b} <- moduleFix(mkAandB);

  Reg#(UInt#(7)) count <- mkReg(0);

  rule run;
    if (count == 10) $finish(0);
    count <= count + 1;
    $display("a: %0d b: %0d count: %0d", a.count, b.count, count);
  endrule

endmodule