The output would be a pulse train though, not a discrete value.<p>You could average that out with a capacitor (which would introduce some latency), then sample the input of the capacitor and output the resulting number. The problem with that approach is that you'll end up with less significance than you'll need for most applications (getting a 10 bit a/d to work reliably is pretty tricky, more bits is voodoo).<p>By the time you follow all this to its logical conclusion I think you'd end up with operational amplifiers.<p>Analogue computers exist, and even existed before digital ones in a certain fashion.<p>They are much more tricky to build and are not as universal as digital computers.