---
Test
---
| script           | lisp interpreter fixture                |
| show  | evaluate | (defun adderx (x) (lambda (y) (+ x y))) |
| show  | evaluate | (setf adder20 (adderx 20))              |
| check | evaluate | (funcall adder20 2)                     | 22 |


| script           | lisp interpreter fixture                |
| #    | Let Over Lambda Over Let Over Lambda                |
| show | evaluate  |!-

(let ((direction 'up))
  (defun toggle-counter-direction ()
    (setq direction
          (if (eq direction 'up)
            'down
            'up)))

  (defun counter-class ()
    (let ((counter 0))
      (lambda ()
        (if (eq direction 'up)
          (setq counter (+ counter 1))
          (setq counter (- counter 1)))))))
                                                           -!|
| show  | evaluate | (setq my-counter (counter-class))       |
| check | evaluate | (funcall my-counter)                    | 1 |
| check | evaluate | (funcall my-counter)                    | 2 |
| check | evaluate | (funcall my-counter)                    | 3 |
| show  | evaluate | (toggle-counter-direction)              |
| check | evaluate | (funcall my-counter)                    | 2 |
| check | evaluate | (funcall my-counter)                    | 1 |
| check | evaluate | (funcall my-counter)                    | 0 |
| show  | evaluate | (toggle-counter-direction)              |
| check | evaluate | (funcall my-counter)                    | 1 |
| check | evaluate | (funcall my-counter)                    | 2 |
| check | evaluate | (funcall my-counter)                    | 3 |