This coding example shows the structural description of a half-Adder composed of four, 2-input nand modules.
module halfadd (X, Y, C, S);
input X, Y;
output C, S;
wire S1, S2, S3;
nand NANDA (S3, X, Y);nand NANDB (S1, X, S3);nand NANDC (S2, S3, Y);nand NANDD (S, S1, S2);assign C = S3;
endmodule