Pass sub function

I am using the function below which summarise data only if column exists.

dummy <- function(df, arrear_var=NULL, pos_var=NULL) {

  if (!missing(arrear_var)) {
    arrear_var <- sym(arrear_var)
  }

  if (!missing(pos_var)) {
    pos_var <- sym(pos_var)
  }

df %>% summarise(lt = if(exists(as_label(enquo(arrear_var)), where = .)) sum(as.numeric(as.character(!!arrear_var)), na.rm = T) else NA,
                 pt = if(exists(as_label(enquo(pos_var)), where = .)) mean(as.numeric(as.character(!!pos_var)), na.rm = T) else NA)
}

dummy(iris, "Sepal.Length", "Petal.Length")

Can I create separate function for this part of code and pass it in above function -

exists(as_label(enquo(var)), where = .)