C. F. Keil and Franz Delitzsch on 1 Samuel 20:9

1Sa 20:9

Jonathan replied, “This be far from thee!” sc., that I should kill thee, or deliver thee up to my father. חלילה points back to what precedes, as in 1Sa 20:2. “But (כּי after a previous negative assertion) if I certainly discover that evil is determined by my father to come upon thee, and I do not tell it thee,” sc., “may God do so to me,” etc. The words are to be understood as an asseveration on oath, in which the formula of an oath is to be supplied in thought. This view is apparently a more correct one, on account of the cop. ו before לא, than to take the last clause as a question, “Shall I not tell it thee?”