source: vis_dev/vis-2.3/models/transition/simple.v @ 40

//typedef enum {ZERO,UN,DEUX} state_t;

module concret(clk,i);
input clk;

reg p;
reg q;
input i;
reg[1:0] state;

initial 
begin
p = 0;
q = 0;
state[1:0] = 0;
end

always @(posedge clk)
begin
case(state)
        0 :
                if(i == 1)
                begin
                        state[1:0] = 1;
                        p = 0;
                        q = 1;
                end
                else
                begin
                        state[1:0] = 2;
                        p = 1;
                        q = 0;
                end
    1 :  if(i == 1)
                begin
                        state[1:0] = 1;
                        p = 0;
                        q = 1;
                end
                else
                begin
                        state[1:0] = 3;
                        p = 1;
                        q = 1;
                end
    2 :  if(i == 1)
                begin
                        state[1:0] = 2;
                        p = 1;
                        q = 0;
                end
                else
                begin
                        state[1:0] = 3;
                        p = 1;
                        q = 1;
                end
    3 :  if(i == 1)
                begin
                        state[1:0] = 2;
                        p = 1;
                        q = 0;
                end
                else
                begin
                        state[1:0] = 3;
                        p = 1;
                        q = 1;
                end

endcase 

end


endmodule