[Ur] obtain signal's value on a server side

[Sergey Mironov]

Hi! I'd like to discuss an issue I faced when I tried to write
function for mapping signals. Compiler answered an error on my attempt
to call [get] function of a [source] group on a server side, where I
tried to get an initial value for a copy of signal from the original
signal

val get : t ::: Type -> source t -> transaction t

I expected that we can think signals are just read-only variables from
the server's point of view. Is absence of server-[get] a vital
restriction?

Regards,
Sergey