| Fold of fold_kind * term * string list * term
(* base case pattern, recursive case bound names, recursive case pattern *)
| Default of term * term (* "some" case pattern, "none" case pattern *)
- | If of term * term (* guard, pattern *)
+ | If of term * term (* guard, body *)
+ | Unless of term * term (* guard, body *)
and pattern_variable =
(* level 1 and 2 variables *)