Importing two (or more) modules which have some predicates with the same name

[leledumbo]

Either I don't understand the explanation in the docs or what, one thing for sure I can't do it correctly. I have:

% module queue
:- module(queue,[empty/1,enqueue/3,dequeue/3,member/2,add_list/3]).

% module set
:- module(set,[empty/1,member/3,member2/3,delete_if_exists/3,add_if_not_exists/3,
          union/3,subset/2,intersection/3,diff/3,equal/2]).

% main module
:- use_module([queue,set]).

when the main module is consulted, swi-prolog says:
ERROR: Cannot import set:empty/1 into module user: already imported from queue

The definition are equal (i.e.: empty([]).), could that be the problem? Should it be possible to call each with a qualified name?

[Eva Stoewe]

> Either I don't understand the explanation in the docs or what, one thing
> for
> sure I can't do it correctly. I have:
>
> % module queue
> :- module(queue,[empty/1,enqueue/3,dequeue/3,member/2,add_list/3]).
>
> % module set
> :-
> module(set,[empty/1,member/3,member2/3,delete_if_exists/3,add_if_not_exists/3,
>           union/3,subset/2,intersection/3,diff/3,equal/2]).
>
> % main module
> :- use_module([queue,set]).
>
> when the main module is consulted, swi-prolog says:
> ERROR: Cannot import set:empty/1 into module user: already imported from
> queue
>
> The definition are equal (i.e.: empty([]).), could that be the problem?
> Should it be possible to call each with a qualified name?

You are not allowed to have two different predicates with the same name in one module. When you use use_module/1 every predicate from those modules (queue, set) that are exported by them become also predicates of the loading module. It does not matter if the definitions are the same.

But there is a way to help you here. You can rename the predicates while loading with use_module(+File, +ImportList).

A completely other way is to make a predicate multifile but I do not think that that is your intention.

Cheers,
  Eva Stöwe.
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[Paulo Moura]

On 2009/10/13, at 14:45, leledumbo wrote:

> Either I don't understand the explanation in the docs or what, one  
> thing for
> sure I can't do it correctly. I have:
>
> % module queue
> :- module(queue,[empty/1,enqueue/3,dequeue/3,member/2,add_list/3]).
>
> % module set
> :-
> module(set,[empty/1,member/3,member2/3,delete_if_exists/
> 3,add_if_not_exists/3,
>          union/3,subset/2,intersection/3,diff/3,equal/2]).
>
> % main module
> :- use_module([queue,set]).
>
> when the main module is consulted, swi-prolog says:
> ERROR: Cannot import set:empty/1 into module user: already imported  
> from
> queue
>
> The definition are equal (i.e.: empty([]).), could that be the  
> problem?

No. You're getting an error because the use_module/1 directive both  
loads the module files and imports their exported predicates. The  
predicates are imported into the current module. For example, if you  
type the query "use_module([queue,set])." at the Prolog prompt, the  
current module is usually the module "user". Thus, the error results  
from trying to import predicates with the same name into the same  
module.

> Should it be possible to call each with a qualified name?


Depends. Do you want instead to load the two module files without auto-
importing their exported predicates?

Cheers,

Paulo


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[leledumbo]

> Depends. Do you want instead to load the two module files without auto-
> importing their exported predicates?

Yes, I want to call all the predicates with qualified names, treating them as singleton objects.

[Jan Wielemaker-3]

On Wednesday 14 October 2009 03:25:24 pm leledumbo wrote:
> > Depends. Do you want instead to load the two module files without auto-
> > importing their exported predicates?
>
> Yes, I want to call all the predicates with qualified names, treating them
> as singleton objects.

In that case the fix is easy:

:- use_module(m1, []).
:- use_module(m2, []).

        Cheers --- Jan

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[leledumbo]

> In that case the fix is easy:
>
> :- use_module(m1, []).
> :- use_module(m2, []).

Thanks. I should've read use_module/2 more carefully.