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Mar 2nd, 2009
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Prolog nested list sum

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Hi everybody, I'm having a little problem with finding sum of nested list in Prolog. So far what I have is
totalSum([],0).
totalSum([H|T],S):-
      totalSum(T,Sum),
      S is Sum + H.
totalSum([H|T],S):-
     totalSum(H,Sum1),
     totalSum(T,Sum2),
     S is Sum1+Sum2.

With first two predicates, I have no problems getting sum of not-nested list. Anybody with a tip as to how I can modify the third predicate so that it can handle nested list? I've tried passing off [H] instead of just H and many other but it hasn't worked so far. Any comment would be deeply appreciated.
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BlackIris is offline Offline
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Mar 2nd, 2009
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Re: Prolog nested list sum

Your second predicate is going to match and override whatever you do in your third predicate. You need to handle nested lists before you handle non-nested lists.
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Rashakil Fol is offline Offline
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Mar 3rd, 2009
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Re: Prolog nested list sum

Thanks for the quick reply. While I agree with you but I have tried with third predicate before second and have encountered the same problem. I think the major problem lies with my logic in third predicate.
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BlackIris is offline Offline
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Mar 3rd, 2009
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Re: Prolog nested list sum

Well you have more problems than just that.
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Rashakil Fol is offline Offline
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Mar 4th, 2009
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Re: Prolog nested list sum

So you mean I have logic problems and more...? Could you point me to a general direction, like where my logic is wrong (I know my logic is flawed but I'm not sure exactly what).
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BlackIris is offline Offline
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Mar 4th, 2009
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Re: Prolog nested list sum

All you need to do to fix your problem is look at your code and imagine what a prolog interpreter would do when interpreting it.
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Rashakil Fol is offline Offline
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