how to use "if" in lisp

how to use "if" in lisp

[Teng Wang]

Hi there,

I just began to learn lisp a couple of weeks ago. It is easy to use,
but sometimes it is really hard to know what variables are in
lisp. And today I want to write a code doing the function as below:

(if (_the major mode is something_)
    (some function)
    (another funcion))

But I don't know how to write down the condition. 

Any suggestions. Thank you all in advance.

---

Teng 

Re: how to use "if" in lisp

[Mirko]

On Nov 15, 1:01 pm, Teng Wang <twang....@gmail.com> wrote:
> Hi there,
>
> I just began to learn lisp a couple of weeks ago. It is easy to use,
> but sometimes it is really hard to know what variables are in
> lisp. And today I want to write a code doing the function as below:
>
> (if (_the major mode is something_)
>     (some function)
>     (another funcion))
>
> But I don't know how to write down the condition.
>
> Any suggestions. Thank you all in advance.
>
> ---
>
> Teng

The variable mode-name contains the name of the major mode (as a
string)

Mirko

Re: how to use "if" in lisp

[Joel J. Adamson]

Teng Wang <twang.umn@gmail.com> writes:

> Hi there,
>
> I just began to learn lisp a couple of weeks ago. It is easy to use,
> but sometimes it is really hard to know what variables are in
> lisp. And today I want to write a code doing the function as below:
>
> (if (_the major mode is something_)
>     (some function)
>     (another funcion))
>
> But I don't know how to write down the condition. 

Since major-mode is local to a buffer, your function should be local to
the buffer.

(symbol-value 'major-mode)

gets the major mode, but there may be a simpler way (i.e. a function
specifically for that).  Read up on symbols and plists.

Joel

-- 
Joel J. Adamson
Biostatistician
Pediatric Psychopharmacology Research Unit
Massachusetts General Hospital
Boston, MA  02114
(617) 643-1432
(303) 880-3109

Re: how to use "if" in lisp

[Joel J. Adamson]

jadamson@partners.org (Joel J. Adamson) writes:

> Teng Wang <twang.umn@gmail.com> writes:
>
>> Hi there,
>>
>> I just began to learn lisp a couple of weeks ago. It is easy to use,
>> but sometimes it is really hard to know what variables are in
>> lisp. And today I want to write a code doing the function as below:
>>
>> (if (_the major mode is something_)
>>     (some function)
>>     (another funcion))
>>
>> But I don't know how to write down the condition. 
>
> Since major-mode is local to a buffer, your function should be local to
> the buffer.

Sorry, that isn't clear: you may need to specify the buffer with
(current-buffer) or otherwise make sure you are dealing with the current
buffer, and to ensure that your function does not affect other buffers.

Joel

-- 
Joel J. Adamson
Biostatistician
Pediatric Psychopharmacology Research Unit
Massachusetts General Hospital
Boston, MA  02114
(617) 643-1432
(303) 880-3109

Re: how to use "if" in lisp

[Teng Wang]

Thank you for your help.

I think about it for a while. I think my design is sort of
nonsense. Since .emacs only be loaded once when start up. When I
change the buffer, it cannot run again.

So now, I am wondering: is there any way to make it run on fly?

----

Teng Wang 

Re: how to use "if" in lisp

[Teng Wang]

Thank you for all your help.

I think I get a workaround.

I can just 
(add-hook '_somemode-hook_
          (my_function)
)

This will do my job.

---
Teng

Re: how to use "if" in lisp

[Xah Lee]

not sure what you mean by "load on the fly". But you can load a elisp
code by a give file with

(load "~/.emacs")

For more emacs lisp lessons, see:

* Emacs Lisp Basics
http://xahlee.org/emacs/elisp_basics.html

* Simple ELisp Grab Bag
http://xahlee.org/emacs/elisp_examples.html

  Xah
  xah@xahlee.org
\xAD\xF4 http://xahlee.org/

Re: how to use "if" in lisp

[Joel J. Adamson]

Teng Wang <twang.umn@gmail.com> writes:

> Thank you for your help.
>
> I think about it for a while. I think my design is sort of
> nonsense. Since .emacs only be loaded once when start up. When I
> change the buffer, it cannot run again.
>
> So now, I am wondering: is there any way to make it run on fly?

(defun this-be-a-function ()
  (interactive)
  (message "This be an interactive function"))

The "(interactive)" in the second line makes it callable by name,
i.e. "M-x this-be-a-function" prints "This be an interactive function"
in the minibuffer.

The Introduction to Emacs Lisp and Elisp manuals are really helpful, and
easy to read.

Joel

-- 
Joel J. Adamson
Biostatistician
Pediatric Psychopharmacology Research Unit
Massachusetts General Hospital
Boston, MA  02114
(617) 643-1432
(303) 880-3109

Re: how to use "if" in lisp

[Tim X]

Teng Wang <twang.umn@gmail.com> writes:

> Thank you for your help.
>
> I think about it for a while. I think my design is sort of
> nonsense. Since .emacs only be loaded once when start up. When I
> change the buffer, it cannot run again.
>
> So now, I am wondering: is there any way to make it run on fly?
>

Can I suggest you let us know what it is you want to do as then we can
possibly give you better alternative solutions. I'm guessing that what you
are really looking for is how to make some elisp run when you enter a
particular mode. If this is the case, what you are looking for is known in
emacs as a 'hook'. Many modes provide various hooks that are run a certain
times, such as wehn a mode is first loaded. Using hooks is one of the
standard ways to customize a mode.

Tim
-- 
tcross (at) rapttech dot com dot au

Re: how to use "if" in lisp

[Teng Wang]

Tim X <timx@nospam.dev.null> writes:

> Teng Wang <twang.umn@gmail.com> writes:
>
>> Thank you for your help.
>>
>> I think about it for a while. I think my design is sort of
>> nonsense. Since .emacs only be loaded once when start up. When I
>> change the buffer, it cannot run again.
>>
>> So now, I am wondering: is there any way to make it run on fly?
>>
>
> Can I suggest you let us know what it is you want to do as then we can
> possibly give you better alternative solutions. I'm guessing that what you
> are really looking for is how to make some elisp run when you enter a
> particular mode. If this is the case, what you are looking for is known in
> emacs as a 'hook'. Many modes provide various hooks that are run a certain
> times, such as wehn a mode is first loaded. Using hooks is one of the
> standard ways to customize a mode.
Yes, I just want to run some function to particular mode, for example:
run abbrev-mode when entering LaTeX-mode. And yesterday I read the
manual again and I found there is LaTeX-mode-hook variable. So now, I
am happy.

But Thank you all the same.
>
> Tim


Best,

----

Teng

Re: how to use "if" in lisp

[Sebastian Tennant]

>>> (if (_the major mode is something_)
>>>     (some function)
>>>     (another funcion))
>>>
>>> But I don't know how to write down the condition. 

This works when evaluated in the scratch buffer:

  (if (equal major-mode 'lisp-interaction-mode)
      (message "yup")
    (message "nope"))

And you could wrap it in a:

 (with-current-buffer STRING-OR-FUNCTION-THAT-RETURNS-A-BUFFER-OR-BUFFER-NAME)

form if you like?

Sebastian