R: 如何获取函数参数的参数

x <- function(x1, x2){

  theCall <- lapply(as.list(match.call()),as.list)[-1]


  args <- lapply(theCall, function(x) as.list(formals(as.character(x))))

  Map(function(a, b) {
    b <- b[-1]

    for (i in seq_along(a)) {
      if(i <= length(b)) a[i] <- b[i]
    }
    a
  }, args, theCall)
}

str(x(a(3,4), b(5)))
#List of 2
# $ x1:List of 2
#  ..$ x: num 3
#  ..$ y: num 4
# $ x2:List of 2
#  ..$ b1: num 5
#  ..$ b2: num 7

显然,即使使用有效的函数调用,也很容易破坏这一点:

str(x(a(3,4), b(,b1 = 5)))
#List of 2
# $ x1:List of 2
#  ..$ x: num 3
#  ..$ y: num 4
# $ x2:List of 2
#  ..$ b1: symbol 
#  ..$ b2: num 5

让此函数对所有可能的输入都正确,这是读者的练习。