match List.nth context (n - 1) with
| (_,C.Decl ty) -> S.lift n ty
| (_,C.Def (_,ty)) -> S.lift n ty
- with Failure _ -> raise (TypeCheckerFailure (lazy "unbound variable")))
+ with Failure _ ->
+ raise (TypeCheckerFailure (lazy ("unbound variable " ^ string_of_int n
+ ^" under: " ^ NCicPp.ppcontext ~metasenv ~subst context))))
| C.Sort (C.Type [false,u]) -> C.Sort (C.Type [true, u])
| C.Sort (C.Type _) ->
raise (AssertFailure (lazy ("Cannot type an inferred type: "^