car, cdr, and push for pairlists in R

pairlist.R

library(inline)
library(microbenchmark)

car <- cfunction(c(x = "pairlist"), '
  if (x == R_NilValue)
    return R_NilValue;
  if (TYPEOF(x) != LISTSXP)
    error("x must be a pairlist");
  return CAR(x);
')

cdr <- cfunction(c(x = "pairlist"), '
  if (x == R_NilValue)
    return R_NilValue;
  if (TYPEOF(x) != LISTSXP)
    error("x must be a pairlist");
  return CDR(x);
')

push <- cfunction(c(x = "pairlist", value = 'ANY'), '
  if (x != R_NilValue && TYPEOF(x) != LISTSXP)
    error("x must be a pairlist");
  return CONS(value, x);
')


n <- 1e4
l <- as.list(1:n)
p <- as.pairlist(1:n)

microbenchmark(
  # Get head item
  z <- l[[1]],
  z <- p[[1]],
  z <- car(p),

  # Add to head
  z <- c(1, l),
  z <- c(1, p),
  z <- push(p, 1),

  # Add to tail
  z <- c(l, 1),
  z <- c(p, 1),

  # Remove from head
  z <- l[-1],
  z <- p[-1],
  z <- cdr(p),

  # Remove from tail
  z <- l[seq_len(length(l) - 1)],
  z <- p[seq_len(length(p) - 1)],

  unit = "us"
)

Any where you post the benchmark result?