fromList :: [a] -> SignalGen (Signal a) fromList xs = stateful xs tail >>= memo . fmap head
1) It does what I want, but is it the good way to do it? Yes, I'd do it the same way, assuming that the input is always an infinite list (so this version should probably be called unsafeFromList...). But you can always make a list infinite, just add a Maybe layer or pad with a default value.
2) Since the returned signal may be used in several places and since I obtain it through the generic fmap (and not through an Elerea primitive), I guessed I had to "memo" it instead of simply using "return". Did I guess right? That's exactly what memo is needed for, yes. However, whether it is worth the overhead in such a simple case (after all, head is essentially just a single dereferencing step) should be determined by profiling.
3) Concerning the functionnality added by the Param implementation, I have the impression that the same can be achieved through the use of an external signal in Simple (*). Am I right? Yes, the two are equally expressive. The difference is the way you access the signals. In the case of Param, you get a globally accessible signal that you don't need to pass around explicitly, just retrieve with 'input' wherever you want. This might be useful when there's some ubiquitous piece of information that you need practically everywhere, e.g. real time for a simulation.
Gergely -- http://www.fastmail.fm - Does exactly what it says on the tin