It would be handy if an aggregate (statistics) could be passed as a function
argument.

$ cat agerr.stp
global a
function printag(ag) {
	if (@count(ag) > 0)
		printf("%d\n", @sum(ag))
}
probe begin {
	a <<< 13
	a <<< 42
	printag(a)
	exit()
}
$ stap agerr.stp
semantic error: probe_1712 with invalid type stats: identifier 'printag' at
agerr.stp:9:2
semantic error: probe_1712 with invalid type stats: identifier 'ag' at :2:18
Pass 2: analysis failed.  Try again with more '-v' (verbose) options.
$