Curious matching fun case

funs.R

fun_wants_num <- function(x) {
  x + 1
}

fun_wants_fun_but_fails <- function(fun) {
  fun(1)
}

fun_wants_fun <- function(fun) {
  fun <- match.fun(fun)
  fun(2)
}


g09 <- function(x, ...) {
  exp(x)
}

g10 <- function() {
  g09 <- 10
  print(g09 + 3)  # used as a value
  print(g09(3))   # used as a function
  print(fun_wants_num(g09))   # used as a value
  print(fun_wants_fun(g09))   # used as a function
  print(fun_wants_fun_but_fails(g09)) # used as a value - error!
}
g10()