func mustSanityCheck(fn *Function, reporter io.Writer) {
	if !sanityCheck(fn, reporter) {
		fn.WriteTo(os.Stderr)
		panic("SanityCheck failed")
	}
}
func mustSanityCheck(fn *Function, reporter io.Writer) {
	if !sanityCheck(fn, reporter) {
		fn.WriteTo(os.Stderr)
		panic("SanityCheck failed")
	}
}
// mustSanityCheck is like sanityCheck but panics instead of returning
// a negative result.
//