Make a reactive variable
Turns a normal variable into a reactive variable, that is, one that has
reactive semantics when assigned or read in the usual ways. The variable may
already exist; if so, its value will be used as the initial value of the
reactive variable (or
NULL if the variable did not exist).
makeReactiveBinding(symbol, env = parent.frame())
a <- 10 makeReactiveBinding("a") b <- reactive(a * -1) observe(print(b())) a <- 20