Re: Make register easier to hook

[Daniel Colascione]

On 3/28/2011 5:52 PM, Leo wrote:
> On 2011-03-29 01:37 +0800, Daniel Colascione wrote:
>> Thanks for doing this work.  An extensible register system is also on my
>> wishlist.  Why did you decide to use the list for the register structure
>> instead of the default vector representation?
>
> Probably because it looks nicer inside register-alist and there is
> little performance to lose.
>
>> Also, have you considered eliminating the `info' slot? Users can
>> construct closures over any necessary variables and assign these
>> closures to the register structure's remaining function slots. After
>> all, we're getting lexbind, and this feature will make constructing
>> closures both easy and safe.
>
> Now I do. But I fail to see how that makes things more convenient. The
> closures must be created inside the command/function that creates the
> register, right? So one won't be able to define functions with defun for
> the slots. Did I miss something?

Well, when we get lexbind, we'll be able to write something like this
safely, cleanly, and efficiency:

(defun foo-register-jump (some-datum)
  "Implement the jump operation for registers with foo values."
  ...
)

(defun foo-register-assign (register some-datum)
  "Assign a foo register value to some register"

  (register-set register
    (register-make
      :jump-func (lambda () (foo-register-jump some-datum))))


Today, we'd have to write this instead for the same effect:

(defun foo-register-assign (register some-datum)
  "Assign a foo register value to some register"
  (lexical-let ((some-datum some-datum)) ; <----- HACK -------<
    (register-set register
      (register-make
        :jump-func (lambda () (foo-register-jump some-datum)))))

I still think the version with lexical-let is cleaner than using a 
separate data value, especially because you can easily close over 
multiple variables without having to build some aggregate data structure 
to hold them.

By the way: I'd also suggest calling the structure register-value or 
somesuch. It's confusing to have the same word refer to the *identifier* 
for the register (a, b, c, ...) and for the thing *inside* a register (a 
window configuration, a marker, a string, etc.)