multiple driver error during simulation

You are right, I am still playing with this code for demo only as I am not aware of your inputs behaviour.

remember you can only detect switch edge one clock period after it rises.

I am not sure if switch will rise once only or many times.

you can run count 0~7 instead of 0 ~ 8 then it will set back to 0 ready waiting for switch to go up again.

if switch = '1' and switch_d = '0' then

count <= 1;

else

count <= count + 1; -- 0~7 free running

end if;

output(count) <= input;

...etc.