This 2-bit adder was a lot of work to build. It uses a total of thirty-six 555 timers and it does have the option of adding or subtracting numbers. It’s a rather unorthodox use of the part, depending ...

Yes, it's generated Verilog, but a generated 1-bit adder works. Also, adding two Vectors fails (input [1:0] a, input [1:0] b, output [2:0] c, assign c = a + b) with "To many input pins".