Difference in query execution in XSB and ErgoAI Studio

[Alex Netkachov]

Hello team.

I've found rather strange difference in behaviour of my query when it is run through XSB command prompt and ErgoAI Studio query window.

Consider the following example:

=== File: example.ergo ===

interface(iCommand).
class(command).
class(asyncCommand).
implements(command, iCommand).
implements(asyncCommand, iCommand).

implementations(?Interface, ?Classes):-
  ?Classes = setof{?Class | implements(?Class, ?Interface)}.

@!{print_implementations(?Type)} !-
  once{implementations(?Type, ?Classes)},
  ?Class \in ?Classes,
  writeln(?Class)@\io.

 

=== end of file ===

In XSB shell:

ergo> add{'C:\\Users\\User\\Projects\\EI\\example'}.
Times (in seconds): elapsed = 0.479; pure CPU = 0.438
Yes
ergo> query{print_implementations(iCommand), 'example.ergo', \@}.
asyncCommand
Times (in seconds): elapsed = 0.008; pure CPU = 0.015

Yes 

Notice that the query only returned one class.

In ErgoAI Studio, however, the result is different when the query is executed through the Ergo Query window (Ctrl+U) - it prints two commands in the Ergo Listener:

asyncCommand
command

Could you please help me understand why it happens and whether it is possible to achieve the same output in XSB shell?

Thanks!

Kind Regards,

Alex

[Michael Kifer]

The thing is that the query window in the studio executes a slightly different query, something like (Query, \false; \true),

which has to do with the peculiarities of the Java interface.

The query window is used mostly to get the explanations. As an query-answer interface to Ergo the query window is quite awkward.

For interactive queries you  should use the studio listener or the ErgoAI shell command window

(what you called "XSB shell"; XSB shell is quite different: it takes only Prolog commands).

--

       --- michael


 

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[Alex Netkachov]

Thank you, I will use the shell for querying.

 

Is there a way to make print_implementations run in the similar way in ErgoAI shell command window? If not, what would be the right way to achieve the same behaviour (run writeln(?Class)@\io for every item in the ?Classes set)? 

Thanks!

Kind Regards,

Alex

[Michael Kifer]

@!{print_implementations(?Type)} !-
  implementations(?Type, ?Classes),
  ?Class \in ?Classes,
  writeln(?Class)@\io,
  !.

should work for that particular query.

--

       --- michael


 

[Alex Netkachov]

I've modified the print_implementations query, but it still writes only one result:

@!{print_implementations(?Type)} !-

  implementations(?Type, ?Classes),

  ?Class \in ?Classes,

  writeln(?Class)@\io,

  !.

ergo> query{print_implementations(iCommand), 'example.ergo', \@}.

asyncCommand

Times (in seconds): elapsed = 0.003; pure CPU = 0.000

Yes

Maybe something else can be changed to make it work as expected?

Thanks!

Kind regards,

Alex

[Michael Kifer]

I thought you wanted the query to give only one answer. Otherwise, why did you use once{...}?

If you want all classes to be printed then

@!{print_implementations3(?Type)} !-
        implementations(?Type, ?Classes),
        ( ?Class \in ?Classes,
          writeln(?Class)@\io,
          \false
        ; \true
        ).

Note that you are trying to play with non-logical side effects (writing) here, so the solution is also not declarative, ie,

a fail-loop like in Prolog. This fail loop is not needed in order to get the answers to the query itself (which is just yes/no here).

--

       --- michael


 

[Alex Netkachov]

It works as I want it to now. Thank you very much for your help!

Kind Regards,

Alex