[racket] Saving and restoring many parameters

I like that better. :)

A minor thing: you could use multiple values and multiple arguments, ie

 > (ps1)
 1
 2

 > (ps1 2 3)
 > (ps1)
 2
 3

 > (ps1 5)
 ... arity error

(You'd still have to use your own version of parameterize, tho, I think.)

Robby

On Fri, Oct 21, 2011 at 9:38 AM, Neil Toronto <neil.toronto at gmail.com> wrote:
> How about this? This code:
>
>    (define p1 (make-parameter 1))
>    (define p2 (make-parameter 2))
>    (define-parameter-group ps1 (p1 p2))
>
> defines a parameter-like group as before, and also defines a 'ps1-value'
> struct. Interaction:
>
>    > (ps1)
>    (ps1-value 1 2)
>    > (ps1 (ps1-value 10 20))
>    > (ps1)
>    (ps1-value 10 20)
>    > (p1)
>    10
>
> Because parameter groups act like a parameter, they can be contained in
> other parameter groups. So the extension mechanism is containment.
>
> You can optionally provide a struct name, and it'll use that instead of
> creating a '<name>-value' struct. (Funny thing: I just discovered it'll take
> 'list' as the struct name, or anything else for which the constructor
> signature and match pattern are the same.)
>
> Is that better?
>
> Neil T
>
> On 10/20/2011 12:36 PM, Robby Findler wrote:
>>
>> What I'm saying is that parameter-list* and parameter-list-append do
>> not seem like things that belong in this API. And it isn't really a
>> "list" in the sense that it is least fixed point of an inductive
>> definition like X = nil | (cons parameter X).
>>
>> Really, there is a new type of data whose purpose is to group together
>> parameters for the purpose of saving and restoring groups of them. So,
>> I think you want one new kind of value (implemented with an opaque
>> struct) that supports those operations (and the name should not
>> include the word "list"). You may also wish to have a way to convert
>> one of these things into a list of parameters, in which case that
>> conversion function would probably have the word "list" in its name,
>> but that'd be a separate thing.
>>
>> Robby
>>
>> On Thu, Oct 20, 2011 at 11:34 AM, Neil Toronto<neil.toronto at gmail.com>
>>  wrote:
>>>
>>> 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
>