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

Hi Richard,

On Oct 3, 2014, at 12:24, Richard A. O'Keefe <[email protected]> wrote:

> 'use_module' comes from Quintus Prolog.
> The way it was intended to be used was
> 
> :- use_module(Module_Name, [
>      Imported_Predicate_1/Arity_1,
>      ...,
>      Imported_Predicate_n/Arity_n
>   ]).
> 
> It was considered to be important for software maintenance
> that you should explicitly list all the predicates you
> needed from the module.  Having done this, the imported
> predicates are then available *without* requiring any prefix.
> 
> This is like the way you do
> 
>    from fractions import Fraction
> 
> in Python, after which you use fractions.Fraction as just
> plain Fraction.
> 
> This is dual to the way that a :- module directive lists
> all the things *exported* from a module.
> 
> The idea was that *all* the stuff relating to modules
> (:- module, :- use_module, :- meta_predicate) should be
> at the very top of a file, and the rest of the file
> should as much as possible look as though modules did
> not exist.

Interesting. Thank you for fresh historical information 
and original idea on module system of Quintus Prolog.

One question.  I want to put meta_predicate directive close 
at the definition  like this.

:- meta_predicate  my_flip(2, ?, ?).    
my_flip(F, X, Y):- call(F, Y, X).

(Though I am not sure whether the  directive is necessary
in this particular case).

Is this a bad practice ?  Or are you saying on  `header information`
for use of external predicates, which sounds reasonable principle.

Kuniaki

> 
> 
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