Shouldn't there be a simple, elegant solution to this problem that doesn't necessitate using ccc and return? Maybe I'm resistant to using continuations because I'm still coming to grips with understanding them... but there's alot of code in arc.arc and only one call to ccc.
You can write a tail-recursive version of tokipin's code pretty easily. Personally though I think this could be an addition to the "examples of LOOP" thread from a while back.
(defun wrandf (xs weights)
(loop with r = (random (apply #'+ weights))
for x in xs
for w in weights
for cw = w then (+ cw w)
when (> cw r) return x))
; assumes pair
(defmacro wrand (&rest args)
`(funcall
(wrandf
(list ,@(mapcar (lambda (x) `(lambda () ,(cadr x))) (pair args)))
(list ,@(mapcar #'car (pair args))))))
