R> require(rpart)
R> fo <- function() for(i in 1:500){rpart(Kyphosis ~ Age + Number + Start, data=kyphosis)}
R> system.time(fo())
# user  system elapsed 
# 1.86    0.00    1.93 
R> require(compiler)
# Loading required package: compiler
R> enableJIT(3)
R> system.time(fo())
#  user  system elapsed 
# 28.14    0.00   28.14 
R> cfo <- cmpfun(fo)
R> system.time(cfo())
# user  system elapsed 
# 27.85   0.00   28.02
R> enableJIT(0)
R> system.time(cfo())
# user  system elapsed 
# 1.71    0.00    1.70