yosys/docs/source/code_examples/show/splice.v

module splice_demo(a, b, c, d, e, f, x, y);

input [1:0] a, b, c, d, e, f;
output [1:0] x;
assign x = {a[0], a[1]};

output [11:0] y;
assign {y[11:4], y[1:0], y[3:2]} =
                {a, b, -{c, d}, ~{e, f}};

endmodule