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Re: Fwd: Tabs for console.

From: Alin Soare
Subject: Re: Fwd: Tabs for console.
Date: Tue, 7 Dec 2010 06:47:33 +0200

> The idea is that I added to struct frame a list of tabs.

Where is it?  In the frame's parameters?  Or is it accessed via a new
frame-tabs and set-frame-tabs?

struct frame
     * an alist  of the form ((alist_tab_parameters))
    Lisp_Object tab_bar_items;

In any case, how difficult would it be to generalize your code so the
tabs can be attached to a window rather than a frame, or even to an
internal window (i.e. internal windows are those that are somewhere
along the window tree and hold various actual windows: currently your
tabs are at the root internal window).

I did not think about. Not too difficult.

> A tab is an alist of

> (
>   (:name "string-name")
>   (:init-code (lambda () ... code) )
>   (:activate-code (lambda() ... code) )
>   (:deactivate-code ... )
>   (:environment list-of-symbols)
> )

What's the init-code for?

The init code is executed only when the tab is created. In my script it is used to memorize the current window config into a variable 'sym. The variable sym must be tab-local during the tab existence.
I suspect activate is run when you click on the tab and deactivate is
run when you click on some other tab.
What's environment and how is it used?

An environment keeps tab-local variables. For example , every tabmust know about the window-configuration when it was created , and extract from its own environment the value of that win config.

No other tab needs to see its own windows config.
> This is the function that defines a tab. It initialize a symbol sym with the
> value of current-window-config. The symbol 'sym is passed to
> (make-terminal-frame), that creates the tab.

I don't understand this "symbol sym" business.

I have just explained. It is not interned in the main obarray, and it is passed to the environment of the tab.

> ;; this is a definition of a tab as a window configuration
> (defun make-wc-tab (parms)
>   ;; save curent win config
>   (setq sym (make-symbol "winconfig"))

Here, you're setting a global variable, which is wrong.  It's also very
unclear why you want a symbol here.

It is not global. It is not interned, and it becomes tab-local.

>   (set sym  (current-window-configuration))
>   ;; make a tab that keeps a window configuration. When it is created,
>   ;; it memorizes the current win config. When it is activated, it
>   ;; restores the memorized win config
>   (make-terminal-frame
>    (list '(tab . t)
>      '(tab:name . "WinC")
>      '(tab:activate
>        .
>        (lambda ()
>          (set-window-configuration
>           (eval (cdr (assoc 'tab:env (frame-parameters) ) ) ) ) ) )

`eval' is bad.  Stay very far away from it.

>      ;; save the current win config into the tab environment
>      (cons 'tab:env sym) ) ) )

How do "tab:activate" and friends relate to the
previous :activate-code thingies?

Via tab-local variables.

In this moment I added code to modify the environment of a tab only via the initialization of the tab with make-terminal-frame, but I can add a function to operate on tab-local variables even after the creation of a tab.

For example, I did not add the tab:init code to tab's alist, because it is runned only to creation, in make-tab, before calling make-terminal-frame.

But if I want to be able to re-initialize a tab, then a function to operate on tab's environment is required.

I don't understand the above call to `make-terminal-frame': does it
create a new frame, or just a new tab?  If the first, then I don't
understand how it works, and if the second, it's wrong because adding
a tab should have nothing to do with frame creation.

The fact that make-tab calls directly make-terminal-frame is just a legacy of the old code, when a tab used to be just a frame.

Imagine that emacs had lexical binding. Then we woud not need a tab environment, because that environment would be included insode the evaluation process, when the closure that represents the tab is initialized. But because emacs is not able of closures, I need a tab environment, to be able to communicate between the

(:init-code (lambda () ... code) )
(:activate-code (lambda() ... code) )
(:deactivate-code ... )

of the same tab,

Note that inside my implementation of make-tab, the variable 'winconfig has a different value for every tab. When :activatecode is called ,

> (lambda ()
>          (set-window-configuration
>           (eval (cdr (assoc 'tab:env (frame-parameters) )

(cdr (assoc 'tab:env (frame-parameters) )  returns the variable 'winconfig, id est sym.

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