; The following should type-check with no errors.

(type-check "

letrec
  (hlistof int) add-one = proc ((hlistof int) lst)
    if null?(lst) then
      emptylist[ int ]
    else
      cons(add1(car(lst)), (add-one cdr(lst)))
in
  (add-one hlist(0,1,2,3,4))

")