creating a function is very costly

CreatingFunction

library(microbenchmark)
microbenchmark(
  do.call = do.call("function", list(as.pairlist(alist(x=)), NULL)),
  eval = eval(call("function", as.pairlist(alist(x=)), NULL)),
  as.function = as.function(alist(x = , NULL)),
  as.function.default = as.function.default(alist(x = , NULL)),
  "function(x) NULL" = function(x) NULL
)
# Unit: nanoseconds
#                expr   min    lq median      uq    max neval
#              do.call 33880 35217  35663 36109.0 166723   100
#                 eval 35217 36554  37000 37446.0  46808   100
#          as.function 46362 47700  48591 49259.5  91831   100
#  as.function.default 28530 29868  29868 30759.0  41458   100
#     function(x) NULL     0     1    446   447.0   4012   100

args_ <- as.pairlist(alist(x=))
body_ <- NULL
argbody1 <- list(args_, NULL)
argbody2 <- alist(x=, NULL)

microbenchmark(
  do.call = do.call("function", argbody1),
  eval = eval(call("function", args_, body_)),
  as.function = as.function(argbody2),
  as.function.default = as.function.default(argbody2),
  "function(x) NULL" = function(x) NULL
)
# Unit: nanoseconds
#                 expr   min    lq median    uq    max neval
#              do.call  5350  5796   6242  6688  20060   100
#                 eval  6687  7579   8470  8917  22290   100
#          as.function 23627 24964  25410 26302 107880   100
#  as.function.default  3567  4013   4013  4459  41904   100
#     function(x) NULL     0   446    446   447   2676   100

args_ <- as.pairlist(alist(x=))
body_ <- 100
argbody1 <- list(args_, body_)
argbody2 <- c(args_, if (is.null(body_)) list(NULL) else body_)

microbenchmark(
  do.call = do.call("function", argbody1),
  eval = eval(call("function", args_, body_)),
  as.function = as.function(argbody2),
  as.function.default = as.function.default(argbody2),
  "function(x) 100" = function(x) 100
)
# Unit: nanoseconds
#                 expr   min    lq  median    uq     max neval
#              do.call  5350  5796  6242.0  6688   18278   100
#                 eval  7133  7579  8470.0  8916 2655064   100
#          as.function 23181 24519 25410.0 25856  111892   100
#  as.function.default  3567  4013  4235.5  4459    5796   100
#      function(x) 100     0   446   447.0   447    2230   100

f1. <- function(..., env = parent.frame()){
  d <- as.pairlist(as.vector(substitute((...)), "list")[-1])
  n <- length(d)
  eval(call("function", as.formals(d[-n]), d[[n]]), env)
}

f2. <- function(..., env = parent.frame()){
  d <- as.vector(substitute((...)), "list")[-1]
  if (length(d) == 0) as.function.default(list(call("{")), env)
  else if (length(d) == 1) as.function.default(d, env)
  else as.function.default(c(as.formals(d[-length(d)]), d[[length(d)]]), env)
}
f1.(x, y, x+y)
f2.(x, y, x+y)
# > identical(f1.(x, y, x+y), f2.(x, y, x+y), ignore.environment=TRUE, ignore.bytecode=TRUE)
# [1] TRUE