is.R()
is.R returns TRUE if we are using R and FALSE
otherwise.
The function has been written such as to correctly run in all versions
of R, S and S-plus.
In order for code to be runnable in both R and S dialects, either
your the code must define is.R or use it as
if (exists(is.R) && is.function(is.R) && is.R()) {
## R-specific code
} else {
## S-version of code
}
version, system.x <- runif(20); small <- x < 0.4 # which only exists in R: if(is.R()) which(small) else seq(along=small)[small]