haystack: ["Zig","Zag","Wally","Ronald","Bush","Zig","Zag","Krusty","Charlie","Bush","Bozo"];
needle:  "Zag";

findneedle(needle, haystack, [opt]):=block([idx],
  idx: sublist_indices(haystack, lambda([w], w=needle)),
  if emptyp(idx) then throw('notfound),
  if emptyp(opt) then return(idx),
  opt: first(opt),
  if opt='f then first(idx) else if opt='l then last(idx) else throw('unknownmode));