Prolog() is does not get a new prolog -- possible to create multiple independent instances?

[Stuart Reynolds]

It seems the Prolog() constructor has side-effects:

from pyswip import Prolog

def test():
    prolog = Prolog()
    prolog.assertz('is_a(a, b)')
    result = list(prolog.query("is_a(a,b)"))
    print(result)
    assert result == [{}]
test()  # OK
test()  # Fail

In the second call is_a(a, b) is in the rulebase twice. Is it possible for second call to instantiate an independent Prolog, or an object with an independent rule base and stack?

- Stuart

[yuce]

Only one instance of SWI-Prolog can be created (limitation of SWI-Prolog) but you can create multiple PySwip modules to emulate the effect of multiple SWI-Prolog instances. There's an example here: https://github.com/yuce/pyswip/blob/master/examples/knowledgebase.py

[Stuart Reynolds]

Thanks!

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[Luke Miller]

Hi, is it possible to use 'consult' with multiple modules somehow? I'd like to load the same .pl file multiple times in my test suite.

[R Zhao]

Would it be possible to support closing the current prolog instance, and then get a clean restart?

I'm imagining a workflow like this:

```

p1 = Prolog()

p1.shutdown()

p2 = Prolog()

...

```

In my use case, each of the queries are independent from each other, so it's very natural to use a clean restart. Previous results and facts shall be discarded to free some resources (not significant, though).

[Stuart Reynolds]

I don’t think the C library allows it

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[R Zhao]

Hmm, that's unfortunate... I'll try other workarounds.

Thanks for the reply.

[yuce]

Have you tried to use multiple knowledge bases? There''s an example at: https://github.com/yuce/pyswip/blob/master/examples/knowledgebase.py

[Stuart Reynolds]

You can assert facts into distinct modules though.

That’s one way of implementing multiple worlds:

mod1:assert(f(1)).

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