vassign

vassign.R

makeActiveBinding("v", local({
  e <- NULL
  count <- 1
  
  function(value) {
    # increment or reinitialize counter
    exec_env <- sys.frame(-1)
    if(identical(e, exec_env)) {
      count <<- count + 1
    } else {
      count <<- 1
      e <<- exec_env
    }
    # fetch function and body
    call <- sys.call(-1)
    caller_env <- sys.frame(-2)
    f <- eval(call[[1]], caller_env)
    calls <- as.list(body(f))[-1]
    # assign
    vpos <- which(sapply(calls, function(x) identical(x, quote(v))))
    value <- eval(calls[vpos - 1][[count]], exec_env)
    var <- as.character(calls[vpos + 1][count])
    assign(var, value, exec_env)
  }
}), .GlobalEnv)


test <- function() {
  1
  v
  x
  
  1 + 1
  v
  y
  
  c(x, y)
}

test()
#> [1] 1 2