foo=function(
    x=1,
    y=2,
    z=3
  ) {

  bar(x,y,z)
}

x=1,
y=2,
z=3

bar(x,y,z)

fxn = function(a, b, d = 2) {}
formals(fxn)
# $a
#
#
# $b
#
#
# $d
# [1] 2

info <- formals(fxn)
for (varname in names(info)) {
  assign(varname, info[[varname]])
}
a
# Error: argument "a" is missing, with no default
b
# Error: argument "b" is missing, with no default
d
# [1] 2