You are seeing a single invocation as running your circuit for a single clock cycle after an arbitrary amount of clock cycles. That's the wrong approach. A single invocation of a circuit takes a stream of values and produces a stream of values. Every invocation start from clock cycle 0.
So yes if your circuit depends on external signals driven by registers living in a different circuit you need to pass those in as inputs. Essentially circuits are composeable just like functions.
A linear feedback shift registers always produces the same stream of values no matter how many times you run it. It's completely pure.
Still, I would be very interested to see how one would implement a shift register, lets say something like the 74HC165, so I can see how the pure functions interact with the register state.
Runnable using replit. To make it as simple as possible I didn't use Clash and used types available in prelude Haskell (Bool instead of bit, 64 bit integer as register state etc. Every single element in the list represent a value coming out of the register on the rising edge of a clock cycle. You can easily extend it if you want latches, enables etc. But that doesn't really change the core point of the code.
Much appreciated. I think I get the gist of it, even though it looks very complex compared to the Verilog counterpart. To be fair, my lack of Haskell knowledge doesn't help.
But it's really helpful to get a feel for the different approach.
I mean Haskell is definitely and acquired taste if you haven't used other languages in the same style before. Also note that writing this in actual Clash would be a one liner. Because stuff like registers and shifts are available as part of the standard library.
I've tried to get into Haskell, and while I don't have a huge problem with the overall concepts most of the time, although a bit alien at times, my brain just can't seem to handle the syntax.
I've found myself thinking differently about code and using a lot more functional-ish concepts when writing my "normal" code though, so I do like the exposure.
So yes if your circuit depends on external signals driven by registers living in a different circuit you need to pass those in as inputs. Essentially circuits are composeable just like functions.
A linear feedback shift registers always produces the same stream of values no matter how many times you run it. It's completely pure.