Programmatic let

Programmatic let

[Lluís]

My elisp foo is quite poor, so this might well be a completely stupid approach
to the problem.

I have a callback that gets automatically called, and uses some orgmode-specific
routines whose behaviour can be tuned through some customizable variables.

The usual approach in orgmode is:

  (let ((org-v1 ...) (org-v2 ...)) (org-func ...))

As my function is automatically called (as a response to the D-Bus message), I'd
like to let the user specify a let-like form to let her temporarily override the
behaviour of the `org-func' that my package invokes:

  (setq my-cb-org-vars '((org-v1 ...) (org-v2 ...)))
  (defun my-cb (...)
    (programmatic-let my-cb-org-vars
      (org-func ...)))

Is it possible to implement `programmatic-let'? And if so, can you throw me a
pointer to the appropriate docs?


Thanks,
  Lluis

-- 
 "And it's much the same thing with knowledge, for whenever you learn
 something new, the whole world becomes that much richer."
 -- The Princess of Pure Reason, as told by Norton Juster in The Phantom
 Tollbooth

Re: Programmatic let

[Grégoire Jadi]

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Lluís <xscript@gmx.net> writes:

> My elisp foo is quite poor, so this might well be a completely stupid approach
> to the problem.
>
> I have a callback that gets automatically called, and uses some orgmode-specific
> routines whose behaviour can be tuned through some customizable variables.
>
> The usual approach in orgmode is:
>
>   (let ((org-v1 ...) (org-v2 ...)) (org-func ...))
>
> As my function is automatically called (as a response to the D-Bus message), I'd
> like to let the user specify a let-like form to let her temporarily override the
> behaviour of the `org-func' that my package invokes:
>
>   (setq my-cb-org-vars '((org-v1 ...) (org-v2 ...)))
>   (defun my-cb (...)
>     (programmatic-let my-cb-org-vars
>       (org-func ...)))
>
> Is it possible to implement `programmatic-let'? And if so, can you throw me a
> pointer to the appropriate docs?

You could use progv:
> (progv SYMBOLS VALUES &rest BODY)
> 
> Bind SYMBOLS to VALUES dynamically in BODY.
> The forms SYMBOLS and VALUES are evaluated, and must evaluate to lists.
> Each symbol in the first list is bound to the corresponding value in the
> second list (or to nil if VALUES is shorter than SYMBOLS); then the
> BODY forms are executed and their result is returned.  This is much like
> a `let' form, except that the list of symbols can be computed at run-time.

However, given a defined set of variables, you could parse
my-cb-org-vars yourself:

(defvar my-cb-org-vars '((x ...) (y ...)))
(defun my-cb (...)
  (let ((x (cdr (assoc 'x my-cb-org-vars)))
        (y (cdr (assoc 'y my-cb-org-vars))))
    ....))

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Re: Programmatic let

[Lluís]

Grégoire Jadi writes:

> Lluís <xscript@gmx.net> writes:
>> My elisp foo is quite poor, so this might well be a completely stupid approach
>> to the problem.
>> 
>> I have a callback that gets automatically called, and uses some orgmode-specific
>> routines whose behaviour can be tuned through some customizable variables.
>> 
>> The usual approach in orgmode is:
>> 
>> (let ((org-v1 ...) (org-v2 ...)) (org-func ...))
>> 
>> As my function is automatically called (as a response to the D-Bus message), I'd
>> like to let the user specify a let-like form to let her temporarily override the
>> behaviour of the `org-func' that my package invokes:
>> 
>> (setq my-cb-org-vars '((org-v1 ...) (org-v2 ...)))
>> (defun my-cb (...)
>> (programmatic-let my-cb-org-vars
>> (org-func ...)))
>> 
>> Is it possible to implement `programmatic-let'? And if so, can you throw me a
>> pointer to the appropriate docs?

> You could use progv:
>> (progv SYMBOLS VALUES &rest BODY)
>> 
>> Bind SYMBOLS to VALUES dynamically in BODY.
>> The forms SYMBOLS and VALUES are evaluated, and must evaluate to lists.
>> Each symbol in the first list is bound to the corresponding value in the
>> second list (or to nil if VALUES is shorter than SYMBOLS); then the
>> BODY forms are executed and their result is returned.  This is much like
>> a `let' form, except that the list of symbols can be computed at run-time.

> However, given a defined set of variables, you could parse
> my-cb-org-vars yourself:

> (defvar my-cb-org-vars '((x ...) (y ...)))
> (defun my-cb (...)
>   (let ((x (cdr (assoc 'x my-cb-org-vars)))
>         (y (cdr (assoc 'y my-cb-org-vars))))
>     ....))

Thanks a lot, `progv' is exactly what I want, given that the list of vars is not
known a priori.


Lluis

-- 
 "And it's much the same thing with knowledge, for whenever you learn
 something new, the whole world becomes that much richer."
 -- The Princess of Pure Reason, as told by Norton Juster in The Phantom
 Tollbooth

Re: Programmatic let

[Burton Samograd]

Lluís <xscript@gmx.net> writes:

> My elisp foo is quite poor, so this might well be a completely stupid approach
> to the problem.
>
> I have a callback that gets automatically called, and uses some orgmode-specific
> routines whose behaviour can be tuned through some customizable variables.
>
> The usual approach in orgmode is:
>
>   (let ((org-v1 ...) (org-v2 ...)) (org-func ...))
>
> As my function is automatically called (as a response to the D-Bus message), I'd
> like to let the user specify a let-like form to let her temporarily override the
> behaviour of the `org-func' that my package invokes:
>
>   (setq my-cb-org-vars '((org-v1 ...) (org-v2 ...)))
>   (defun my-cb (...)
>     (programmatic-let my-cb-org-vars
>       (org-func ...)))

This should work:

(defmacro programmatic-let (vars &rest body)
    `(let ,vars
          ,@body))

--
Burton Samograd