identifying which predicate failed

[Dan]

Hello, 

In checking the properties of a structure I have property identification tests, each comprising a number of predicates. The structure exhibits a property when all predicates succeed, and  not, if at least one in the series of predicates fails. 

This looks something like this:

property_test(p1) :-

  test1(S, X, Y),

  test2(S, Y, Z),

  test3(S, Z, _M).

Typically, this involves a lot of backtracking, before success or failure can be determined.

If there is failure I want to know which predicates failed the property test. 

I tried an -> structure wrapped around a single test predicate, but I think this wont work because tests fail and backtrack and can then succeed. An if structure would abort the next trials. 

nop.

property_test(p1) :-

  (test1(S, X, Y)-> nop; message(1)), 

  (test2(S, Y, Z),-> nop; message(2)),

 (test3(S, Z, _M) -> nop; message(3)).

Any suggestion are most welcome, 

thank you,

Dan

[Paul Singleton]

You cannot prove a negative - if a goal fails it is because no proof was found - there is no particular reason why.

But suppose you could capture all the explored paths of your unsuccessful search: which ones are significant to you? You need to formalise this.

Then you need a Prolog-in-Prolog interpreter which logs failed branches of the proof.

Perhaps start by playing with spypoints and leashing?

Paul Singleton

[Paulo Moura]

Hi Dan,

Something along the lines of the assertion/1 predicate may help:

http://www.swi-prolog.org/pldoc/doc_for?object=assertion/1

Cheers,
Paulo

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[Barb Knox]

How about:

property_test(p1) :-

   (  nb_setval(failed, test1),

      test1(S, _X, Y),

      %

      nb_setval(failed, test2),

      test2(S, Y, Z),

      %

      nb_setval(failed, test3),

      test3(S, Z, _M)

   )

-> true % All test predicates succeed.

;  nb_getval(failed, Test),

   message(p1, Test),

   fail.

   

thank you,

HTH.

Dan

-- 

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|  BBB                b    \    Barbara at LivingHistory stop co stop uk
|  B  B   aa     rrr  b     |
|  BBB   a  a   r     bbb   |   ,008015L080180,022036,029037
|  B  B  a  a   r     b  b  |   ,047045,L014114L4.
|  BBB    aa a  r     bbb   |
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[Dan]

Hi Barb, 

This code looks beautiful!

thank you,

Dan