[racket] Saving and restoring many parameters

Good. I'm glad we avoided the unknown boogeyman.

But I don't see why you need tangle lists and these things.

Robby

On Thu, Oct 20, 2011 at 10:54 AM, Neil Toronto <neil.toronto at gmail.com> wrote:
> On 10/20/2011 08:08 AM, Robby Findler wrote:
>>
>> Well, what about the current-namespace? The output ports? It seems
>> dangerous and leak introducing (possibly).
>>
>> I don't actually have an example where it could cause a problem tho. But
>> you might try to think thru the ramifications by searing for "current-"
>> in the docs.
>
> I still think using a thread wouldn't be a problem. But you convinced me
> yesterday that it could become a problem in the future.
>
> So I invented parameter lists. Creating a plot pict looks like this now:
>
>    (define saved-parameters (plot-parameters))
>    (dc (λ (dc x y)
>          (parameterize/list ([plot-parameters  saved-parameters])
>            (plot/dc renderer-tree dc x y width height ...)))
>        width height)
>
> Some example tests:
>
>    (define p1 (make-parameter 1))
>    (define p2 (make-parameter 2))
>    (define ps1 (parameter-list p1 p2))
>
>    (check-equal? (ps1) (list 1 2))
>    (check-equal? (parameterize/list ([ps1  (list 10 20)]) (ps1))
>                  (list 10 20))
>    (check-equal? (parameterize ([p1 10] [p2 20]) (ps1))
>                  (list 10 20))
>    (check-equal? (parameterize/list ([ps1  (list 10 20)])
>                    (list (p1) (p2)))
>                  (list 10 20))
>
>    (ps1 (list 10 20))
>
>    (check-equal? (ps1) (list 10 20))
>
> Rules:
>
>    ((parameter-list p ...)) = (list (p) ...)
>
>    ((parameter-list p ...) (list v ...)) = (begin (p v) ...)
>
>    (parameterize/list ([(parameter-list p ...)  (list v ...)]) e ...)
>     = (parameterize ([p v] ...) e ...)
>
>    ((parameter-list* p ... pl)) = (list* (p) ... (pl))
>
>    ((parameter-list-append pl ...)) = (append (pl) ...)
>
> I know Blake has wanted these before, so I might throw them into unstable.
>
> Neil T
>