Re: TODO dependencies

[Carsten Dominik <carsten.dominik@gmail.com>]

Hi

I am curious why I never got any feedback on this implementation
of task dependencies.  Did people overlook this?  Or is the need
for dependencies not as pressing as some of you thought?

- Carsten

On Oct 19, 2007, at 8:27 AM, Carsten Dominik wrote:

> On Oct 11, 2007, at 16:46, Carsten Dominik wrote:
>
>> - concerning the TRIGGER proposal by John, and the TRIGGER/BLOCKER  
>> functionality
>>  discussed later:  In Emacs terms, this seems to translate into a  
>> *hook*
>>  that is called at the right moment.  I'd say that a single hook is  
>> enough.
>>  The right moment to call it would be when Org-mode has figured out  
>> everything
>>  about a change that is about to occur, but before actually doing it.
>>  We can be general what kind of change this could be, a TODO state  
>> change,
>>  adding a tag, setting a property, changing the priority, anything  
>> really.
>
>>  So we would have a property that contains a Lisp form, and that  
>> lisp form would
>>  be evaluated at that moment.
>>  TRIGGER would then mean to perform actions in other entries.
>>  BLOCKER would mean to query other entries for information, and, if  
>> necessary,
>>  abort the current action, for example by throwing to a specified  
>> catch form.
>>  Obviously, if you nee both triggers and blockers, the blockers  
>> need to run
>>  first, but we don't need separate properties/functions for this.
>>
>>  The detailed implementation would then be a number of Lisp  
>> functions that
>>  take as arguments a *single* structure that contains all the info  
>> of the change,
>>  for example a property list like
>>
>>      (list :type 'TODOSTATE :from nil %to "INPROGRESS" ....
>
> Due to the controversial nature of the discussion on this subject,
> it seems to be better, for the time being, to keep this functionality
> outside the core of org-mode.  Other reasons for this are that the
> free-form nature of Org-mode files do make it non-trivial to implement
> dependencies in a bullet-proof way.
>
> I will actually take still another step back from the proposals we
> discussed:  I'd like to not even fix the properties that should be
> used for dependencies.
>
> Instead, I am proposing and starting up the following route:
>
> Org-mode version 5.13 contains two new hooks, `org-blocker-hook' and
> `org-trigger-hook'.  These hooks are called before and after a state
> change, respectively.  Currently only TODO state changes will do
> this, but more could be added in the future.
>
> The blocker hook is able to block a state change, the trigger
> hook just happens after the change.  This is all that will go into
> the core for now.
>
> While this may seem little, it actually opens the dore wide for
> a number of dependency extensions to be written, with free
> choice of properties to be used and the "language" applied in
> these properties to describe dependencies.  In this way
> we can have different implementations working alongside without
> conflicts.
>
> As a proof of concept, I am providing a small file org-depend.el.
> This is not meant as a definition of how things should be, but
> as an inspiration to people who want to try their teeth at this.
>
> Nevertheless, this small set of functions already does most of
> what at least some of you have been asking for:  It introduces
> the concept of chaining a sequence of TODO entries together by
> insinuating only the first entry in the chain.
> It also allows for entries to be identified by an :ID: property,
> and this property to be used to trigger or be blocked by entries
> in arbitrary places in the current file.  So I hope it will be a
> good starting point, I have tried to comment it well enough
> so that hacking should be easy.
>
> Here is a copy of the documentation from that file.  The file
> itself is available at http://orgmode.el/org-depend.el.
>
> - Carsten
>
> ---8><-------------------------------------------------------- 
> ><8------
>
> WARNING: This file is just a PROOF OF CONCEPT, not a supported part
>         of Org-mode.
>
> This is an example implementation of TODO dependencies in Org-mode.
> It uses the new hooks in version 5.13 of Org-mode,
> `org-trigger-hook' and `org-blocker-hook'.
>
> It implements the following:
>
> Triggering
> ----------
>
> 1) If an entry contains a TRIGGER property that contains the word
>   "chain-siblings", then switching that entry to DONE does the
>   following:
>   - The sibling following this entry is marked DONE.
>   - The sibling also get the "chain-sibling" property, to make
>     sure that, when *it* is DONE, the chain will continue.
> 2) If the TRIGGER property contains any other words, these are
>   treated as entry id's.  That means, Org-mode will search for an
>   entry with the ID property exactly equal to this word, and
>   switch that entry to TODO as well.
>
> Blocking
> --------
> 1) If an entry contains a BLOCKER property that contains the word
>   "previous-sibling", the sibling above the current entry is
>   checked.  If it is still in a TODO state, the current state
>   change is blocked.
> 2) If the BLOCKER property contains any other words, these are
>   treated as entry id's.  That means, Org-mode will search for an
>   entry with the ID property exactly equal to this word, and make
>   sure that this entry is done as well, before allowing the state
>   change to occur.
>
> Example:
> --------
>
> When trying this example, make sure that the settings for TODO  
> keywords
> have been activated, i.e. include the following line and press C-c C-c
> on the line before working with the example:
>
> * TODO Win a million in Las Vegas
>  The "third" TODO (see above) cannot become a TODO without this money.
>
>  :PROPERTIES:
>    :ID: I-cannot-do-it-without-money
>  :END:
>
> * Do this by doing a chain of TODO's
> ** TODO This is the first in this chain
>   :PROPERTIES:
>     :TRIGGER: chain-siblings
>   :END:
>
> ** This is the second in this chain
>
> ** This is the third in this chain
>   :PROPERTIES:
>     :BLOCKER: I-cannot-do-it-without-money
>   :END:
>
> ** This is the forth in this chain
>   When this is DONE, we will also trigger entry XYZ-is-my-id
>  :PROPERTIES:
>    :TRIGGER: XYZ-is-my-id
>  :END:
>
> ** This is the fifth in this chain
>
> * Write report
>  :PROPERTIES:
>    :ID: XYZ-is-my-id
>  :END:
>
>
>
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