[racket] Saving and restoring many parameters

Is there a better data type to tangle them with?

I considered multiple values, but those were cumbersome to save because 
(values v ...) isn't a first-class value. Saving and restoring multiple 
parameters is the main reason to use a parameter list.

I tried making structs, but that forced me into making a 
'define-parameter-list' macro instead of a 'parameter-list' function. I 
wanted as much similarity with parameters as possible.

It turned out that 'list*' and 'append' have well-known semantics that 
correspond nicely with extending and combining parameter lists.

I suppose I could use a prefab struct instead.

Neil T

On 10/20/2011 09:59 AM, Robby Findler wrote:
> 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
>>