El Tue, Oct 27, 2009 at 11:23:44PM -0400, Stefan Monnier ens deleità amb les següents paraules:
> > Are you looking for examples of hooks that would be needed, or examples
> > of behaviors that need hooks to be designed?
> 
> Examples of hooks that could make such things possible.

Ok, so here's a high-level shot on a possible completion infrastructure.

Note that much of what I describe is oriented towards programming.

* Completion candidates
** Information
   Contains whatever information the system could gather about the symbol. When
   programming with semantic activated, this could be the semantic tag structure.
** Actions
   Various actions that can be applied on a candidate.
   This is basically the interface to view the candidate information.
*** get-*
    Recollect the interesting bits from information, so that the user can easily
    access it independently of the "information backend" (e.g., semantic tags).
**** get-name
     Candidate name
**** get-location
     Where the candidate has been defined
**** get-return
     Return type of the candidate (only meaningful on programming candidates)
**** get-arguments
     Arguments of the candidate (idem)
**** get-short-help
     Short version of candidate help
**** get-long-help
     Long version of candidate help
*** show
    Shows an arbitrary composition of get-*.
    E.g., (concat (get-signature candidate) "\n" (get-long-help candidate))
    Where that sould be shown, must be user selectable (see below
*** insert-*
    Insert "something" at point (cannot think of use-cases where insertion takes
    place in other places other than point).
**** insert-name
     Insert the good old completion candidate name.
**** insert-template
     Insert a "template" based on the candidate information.
     E.g.,
        open(<<const char *pathname>>, <<int flags>>)
     The <<...>> parts are yasnippet-like placeholders for the user to fill.
     This could be complicated even more, like:
       * insert a placeholder for the result if compeltion is at first non-blank
         column.
       * insert ";" at end if completion is at first non-blank column.
       * show parameter/return help (e.g., when help follows doxygen style) when
         moving between placeholders.
* UI
** Types
   The completion-ui package has implementations for some (if not all) of them.
   The UI 
*** buffer
    Is the current *Completions* buffer.
*** minibuffer
    The completion system used by, e.g., predictive-mode.
*** overlay
    That's the one I prefer, see company-mode as an example.
*** others
    There are many others, like menus, etc.
** Operations
   All action triggered by operations should be possibly be configured on a
   per-information-backend basis (e.g., completions from yasnippet do not have
   any meaningful `get-return').
*** start
    Start the completion process. E.g.:
        (show current-ui get-return get-name get-arguments)
    would show the full signature of a function.
*** focus
    Let's the user "highlight" an entry of the possible candidates. It's the
    good old next/prev in an overlay UI.
    Focusing an element can trigger other actions. This will mainly be
        (show <where> ...)
    The <where> could be any of minibuffer, another buffer, tooltip, etc.
*** select
    Called when the user selects a candidate. This can trigger insert and/or
    show actions.
    In fact, triggering only show actions could be used to reuse this very same
    infrastructure for other purposes other than completion, like a
    user-configurable tool to show help on symbol at point.
*** completion-map
    Extra actions the user can trigger through keyboard when the completion UI
    is "active".
    E.g., i can focus to an interesting symbol and trigger
        (show some-buffer get-long-help)

This probably means a whole lot of coding and I'm neither knowledgeable of
current state of functionalities nor proficient in elisp.

Just a thought,
    Lluis

-- 
 "And it's much the same thing with knowledge, for whenever you learn
 something new, the whole world becomes that much richer."
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 Tollbooth