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.toro...@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
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