Re: goal_expansion

On 02/10/2014 04:19 PM, Carlo Capelli wrote:
> Hi Jonathon
>
>  From my self-learner experience (mainly
> lifter<https://github.com/CapelliC/prolog-snippets/blob/master/lifter.pl>)
> I have an hint - maybe useful only if you use XPCE IDE - or anything
> similar...
> I think you'll need to place near bottom of source a condition
>
> :- multifile user:goal_expansion/2.
> user:goal_expansion(X, Y) :-
> 	\+ current_prolog_flag(xref, true),
> 	... your_code
>
> Indeed, I experienced IDE freezing with a 'cross-referencing buffers'
> message before I discovered that trick - in library(clpfd), if I recall
> rightly.

For simple cases this is typically not needed, but some of these
goal expansion rules either have side effects (dubious) or are
anticipate a particular structure of the source being processed.
The IDE will call these things in a rather arbitrary order and
assume they are pure relations without side effects.  If that
is not the case, you need this extra condition.

	Cheers --- Jan

P.s.	It seems though that Jonathon wants to rewrite source
	files.  If this is the case, goal_expansion/2 is not
	for you.  It is there, such that you can write human
	readable code that actually needs to be something hard
	to read and write.  To me, that is the opposite, but
	perhaps I didn't understand the OP.

>
> bye Carlo
>
>
>
> 2014-02-09 1:46 GMT+01:00 Jonathon Doran <[email protected]>:
>
>> I would very much like to see a simple example of the use of
>> goal_expansion.
>>
>> I have a large program, and I would like to make a series of changes.  I
>> see that I am following the same pattern each time, and if I were writing
>> in another language I would consider creating a macro.
>>
>> This may be the wrong technique to use in Prolog, but I'm curious if it
>> would be possible.
>>
>> For example:  A list is passed to a predicate, and the list is checked for
>> an optional member (may or may not be there).  If the member is in the
>> list, we use it.  If not, a default value is used.
>>
>> Writing the code by hand I might do:
>>
>>     (
>>        \+ member(color:Color, List) ->
>>               random_color(Color)
>>         ;
>>               true
>>     ),
>>
>>
>> I am wondering if I can clean that up to something more readable via
>> goal expansion.
>>
>> (This may be a dumb way to go about things, but I would rather not rewrite
>>   a huge chunk of existing code)
>>
>> Thanks,
>> Jonathon Doran
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