R help - Mar 2012 - tryCatch in a package

Hi,

Suppose we have a general function that returns a logical indicating
which values in 'x' are found in 'l', throwing an error if none
are
found and a warning if only some are found:

"checkFun" <- function(l, x)
{
    xinl <- x %in% l
    if (! any(xinl)) stop("none of the x values found in l")
    if (any(! xinl))
        warning("x ", x[! xinl], " do(es) not exist")
    xinl
}

This function would be used in several other functions that need to stop
and throw the error message or give the warning and use the logical
value, as here:

"getListElement" <- function(k, y) {
    tryCatch({
        ok <- checkFun(names(k), y)
        dm <- k[y[ok]]
        if (length(y) == 1L) dm[[1]] else dm # just to simplify if only 1
    })
}

K <- list(A=1, B=2, C=3)
Y <- LETTERS[1:5]
getListElement(K, Y)

Is this good practice in a package, or should the functionality of
checkFun() be implemented inside tryCatch via the different handlers?

Thanks,

-- 
Seb