Possible to conditionally bind variable?

Possible to conditionally bind variable?

[Tory S. Anderson]

I have several redundancies in the following code: 

(defun go-or-make-agenda (&optional new-frame)
  (interactive "P")
  (let ((buffer "\*Org Agenda\*"))
    (if (get-buffer buffer)
	(if new-frame
	    (switch-to-buffer-other-frame buffer)
	  (switch-to-buffer buffer))
      (if new-frame
	  (switch-to-buffer-other-frame org-agenda-list)
	(org-agenda-list)))))

I'd like to do something like the following, to chop out much of the switch-to-[other-]-buffer cruft:

(defun go-or-make-agenda (&optional new-frame)
  (interactive "P")
  (let ((buffer "\*Org Agenda\*")
	(some-other-buffer "*scratch*")
	(my-switch-function (if new-frame ;; is there some way to do this?
				'(switch-to-other-buffer)
				'(switch-to-buffer)))
    (if (get-buffer buffer)
	(my-switch-function buffer)
	(my-switch-function some-other-buffer))))) 


 I'm not sure this is possible (short of the rather daunting http://stackoverflow.com/questions/25115876/conditional-variable-binding-in-common-lisp), but I have trust that in the awesomeness of Lisp it just might be.

- Tory 

Re: Possible to conditionally bind variable?

[Nicolas Richard]

torys.anderson@gmail.com (Tory S. Anderson) writes:
> (defun go-or-make-agenda (&optional new-frame)
>   (interactive "P")
>   (let ((buffer "\*Org Agenda\*")
> 	(some-other-buffer "*scratch*")
> 	(my-switch-function (if new-frame ;; is there some way to do this?
> 				'(switch-to-other-buffer)
> 				'(switch-to-buffer)))
>     (if (get-buffer buffer)
> 	(my-switch-function buffer)
> 	(my-switch-function some-other-buffer))))) 

untested :

(defun go-or-make-agenda (&optional new-frame)
  (interactive "P")
  (let ((buffer "\*Org Agenda\*")
	(some-other-buffer "*scratch*")
	(my-switch-function (if new-frame ;; is there some way to do this?
				'switch-to-buffer-other-frame
                              'switch-to-buffer)))
    (if (get-buffer buffer)
        (funcall my-switch-function buffer)
      (funcall my-switch-function some-other-buffer))))

HTH,

-- 
Nicolas Richard

Re: Possible to conditionally bind variable?

[Stefan Monnier]

> (defun go-or-make-agenda (&optional new-frame)
>   (interactive "P")
>   (let ((buffer "\*Org Agenda\*")
>         (some-other-buffer "*scratch*")
>         (my-switch-function (if new-frame ;; is there some way to do this?
>                                 'switch-to-buffer-other-frame
>                               'switch-to-buffer)))
>     (if (get-buffer buffer)
>         (funcall my-switch-function buffer)
>       (funcall my-switch-function some-other-buffer))))

Aka

   (defun go-or-make-agenda (&optional new-frame)
     (interactive "P")
     (let ((buffer "\*Org Agenda\*")
           (some-other-buffer "*scratch*")
           (my-switch-function (if new-frame ;; is there some way to do this?
                                   'switch-to-buffer-other-frame
                                 'switch-to-buffer)))
       (funcall my-switch-function
                (if (get-buffer buffer) buffer some-other-buffer))))

Aka

   (defun go-or-make-agenda (&optional new-frame)
     (interactive "P")
     (let ((buffer "\*Org Agenda\*")
           (some-other-buffer "*scratch*"))
       (funcall (if new-frame 'switch-to-buffer-other-frame 'switch-to-buffer)
                (if (get-buffer buffer) buffer some-other-buffer))))

-- Stefan

Re: Possible to conditionally bind variable?

[Tory S. Anderson]

Wow! It works! 

So, I forgot the funcall my first time and it didn't work; it said "Symbol's function definition is void: my-switch-function". How do the funcalls fix it? I thought the first item in parens was automatically called as a function unless quoted? 

Lisp FTW

Nicolas Richard <theonewiththeevillook@yahoo.fr> writes:

> torys.anderson@gmail.com (Tory S. Anderson) writes:
>> (defun go-or-make-agenda (&optional new-frame)
>>   (interactive "P")
>>   (let ((buffer "\*Org Agenda\*")
>> 	(some-other-buffer "*scratch*")
>> 	(my-switch-function (if new-frame ;; is there some way to do this?
>> 				'(switch-to-other-buffer)
>> 				'(switch-to-buffer)))
>>     (if (get-buffer buffer)
>> 	(my-switch-function buffer)
>> 	(my-switch-function some-other-buffer))))) 
>
> untested :
>
> (defun go-or-make-agenda (&optional new-frame)
>   (interactive "P")
>   (let ((buffer "\*Org Agenda\*")
> 	(some-other-buffer "*scratch*")
> 	(my-switch-function (if new-frame ;; is there some way to do this?
> 				'switch-to-buffer-other-frame
>                               'switch-to-buffer)))
>     (if (get-buffer buffer)
>         (funcall my-switch-function buffer)
>       (funcall my-switch-function some-other-buffer))))
>
> HTH,

Re: Possible to conditionally bind variable?

[Nicolas Richard]

torys.anderson@gmail.com (Tory S. Anderson) writes:

> Wow! It works! 
>
> So, I forgot the funcall my first time and it didn't work; it said
> "Symbol's function definition is void: my-switch-function". How do the
> funcalls fix it? I thought the first item in parens was automatically
> called as a function unless quoted?

(info "(elisp) Classifying Lists") and (info "(elisp) Symbol
Components") will help you somewhat.

-- 
Nico.

Re: Possible to conditionally bind variable?

[Rusi]

On Thursday, September 11, 2014 7:24:19 PM UTC+5:30, Nicolas Richard wrote: (Tory S. Anderson) writes:

> > Wow! It works! 
> > So, I forgot the funcall my first time and it didn't work; it said
> > "Symbol's function definition is void: my-switch-function". How do the
> > funcalls fix it? I thought the first item in parens was automatically
> > called as a function unless quoted?

> (info "(elisp) Classifying Lists") and (info "(elisp) Symbol
> Components") will help you somewhat.

Also, more conceptually:
http://en.wikipedia.org/wiki/Common_Lisp#The_function_namespace

Re: Possible to conditionally bind variable?

[Rusi]

On Thursday, September 11, 2014 6:04:33 PM UTC+5:30, Stefan Monnier wrote:
> > (defun go-or-make-agenda (&optional new-frame)
> >   (interactive "P")
> >   (let ((buffer "\*Org Agenda\*")
> >         (some-other-buffer "*scratch*")
> >         (my-switch-function (if new-frame ;; is there some way to do this?
> >                                 'switch-to-buffer-other-frame
> >                               'switch-to-buffer)))
> >     (if (get-buffer buffer)
> >         (funcall my-switch-function buffer)
> >       (funcall my-switch-function some-other-buffer))))

> Aka

>    (defun go-or-make-agenda (&optional new-frame)
>      (interactive "P")
>      (let ((buffer "\*Org Agenda\*")
>            (some-other-buffer "*scratch*")
>            (my-switch-function (if new-frame ;; is there some way to do this?
>                                    'switch-to-buffer-other-frame
>                                  'switch-to-buffer)))
>        (funcall my-switch-function
>                 (if (get-buffer buffer) buffer some-other-buffer))))

> Aka

>    (defun go-or-make-agenda (&optional new-frame)
>      (interactive "P")
>      (let ((buffer "\*Org Agenda\*")
>            (some-other-buffer "*scratch*"))
>        (funcall (if new-frame 'switch-to-buffer-other-frame 'switch-to-buffer)
>                 (if (get-buffer buffer) buffer some-other-buffer))))

Seeing this beautiful code, cant help making the remark:
This is called functional programming; guys like Stefan do it
guys like talk about it.

Here is some more talk -- what Stefan has demoed above is one of the
many cases outlined there:

http://blog.languager.org/2012/10/functional-programming-lost-booty.html

Re: Possible to conditionally bind variable?

[Rusi]

On Friday, September 12, 2014 9:25:46 AM UTC+5:30, Rusi wrote:
> On Thursday, September 11, 2014 6:04:33 PM UTC+5:30, Stefan Monnier wrote:

> >    (defun go-or-make-agenda (&optional new-frame)
> >      (interactive "P")
> >      (let ((buffer "\*Org Agenda\*")
> >            (some-other-buffer "*scratch*"))
> >        (funcall (if new-frame 'switch-to-buffer-other-frame 'switch-to-buffer)
> >                 (if (get-buffer buffer) buffer some-other-buffer))))

> Seeing this beautiful code, cant help making the remark:
> This is called functional programming; guys like Stefan do it
> guys like talk about it.

that should have been "guys like me talk about it." :-)