Design By Contract LIbrary(ies) for Common Lisp?

Question

Coming from a background in Clojure, I am taken with the potential that its pre-/post-conditions provide as a basis for design by contract:

;; sqr.clj

(defn sqr [n]
  {:pre  [(not= 0 n) (number? n)]
   :post [(pos? %) (number? %)]}
  (* n n))

(sqr 10)
;=> 100

(sqr 0)
; Assertion error

Is there a similar pre/post capability in Common Lisp and/or a more comprehensive Design by Contract library available in the wild?

Thank you

Erkan

Answer 1

it is relatively trivial to write a macro that can be used like this:

(defun sqr (n)
  (with-dbc-checked
     (:pre  ((not (zerop n)) (numberp n))
      :post ((plusp %) (numberp %)))
    (* n n)))

For CLOS generic functions, see here: http://www.muc.de/~hoelzl/tools/dbc/dbc-intro.html

Btw., from this code it can be seen that there is zero code exchange is possible between CL and Clojure, without rewriting anything completely.

Profound

This is precisely the library that I was looking for. Thank you. – Erkan

Answer 2

You can assert:

(defun sqr (n)
  (assert (and
           (not (zerop n))
           (numberp n)))
  (* n n))

Don't know exactly what the post part is ment to do. :)

Nunciata