(examples-for ensure
  ("always gets called on the way out"
   (let x 10
     (ensure (assign x (+ x 11))
             (assign x (+ x 22)))
     x)
   43))

(examples-for on-err
  ("'handles errors"
   (let x nil
     (on-err (= x "impossible")
             (= x (nil nil nil)))
     x)
   "impossible")

  ("handles nested errors"
    (on-err (joinstr "\n" errors)
            (on-err (error "foo")
                    (on-err (error "bar")
                            (on-err (error "toto")
                                    (error "primum errorum")))))
    "foo
bar
toto
primum errorum")

  ("handles errors but any ensuring clause gets called first"
   (with (x nil y nil)
         (on-err (= x 'impossible)
                 (ensure (assign y 'ensure-clause)
                         (nil nil nil)))
         (list x y))
   (impossible ensure-clause)))