Re: predutils package available (Re: PAC library for develop version available)

Hi Kuniaki,

I've deleted the predutils registration.

?- pack_install(pac) works fine here.

I didn't really look into the details why the pack is not processed,
but quite likely it has to do with modulariry and operator usage.  The
pac package adds a lot of really generically named files to your library,
a number of which are not modules and seem  to fulfil diverse roles.

Things that server example purposes should go into a directory
`examples` instead of into the prolog directory.  Files there are
not analysed and do not end up in your (extended) Prolog library,
so you can put there whatever you like.

Helper files should also be banned from the prolog directory, especially
if they have generic names.  Many classical programs have a file `util.pl`.
If we allow for that habbit it packs, library(util) will be ambiguous.
The normal solution is to create a subdirectory, so you get

pac
  pac/prolog/pac.pl
  pac/prolog/pac/reduce.pl

Any .pl file below pac/prolog should be a module file and should use
:- use_module(...) to get its requirements.  The helper modules in
prolog/pac should typically start with e.g., :- module(pac_reduce, ...)
to avoid name conflicts.  Modules should export whatever needs to be
accessible from the outside, including operators.  Code using modules
should import the module using use_module/1 or use_module/2 and use
non-qualified calls.

A good thing to read is Michael Richter's tutorial on modules.

Writing libraries is a different thing than writing a program in user
space ...  I hope this helps

		--- Jan

On 10/01/2014 08:49 AM, Kuniaki Mukai wrote:
>> > This is needed because library(predutils) doesn't export the predicates
>> > from module pac.  The documentation on modules should help:
>> > http://swi-prolog.org/pldoc/man?section=modules
> Thanks. I will reread it.  Once I had some difficulty to understand
> basic notions on module something like difference between "namespace"  
> or "predicatebase". So I skipped it as my usual way. 
> I feel I have been paying to the skipping.  
> For instance, it is only recent (few hours ago !) for me to notice that 
> assert(a:(b:-c)) is not equivalent to  assert(a:b :- c).