On 1/31/2018 2:51 PM, Matthias Felleisen wrote:
> On Jan 31, 2018, at 2:15 PM, George Neuner <[email protected]> wrote:
>
>
> On 1/31/2018 2:10 PM, Sam Caldwell wrote:
>> Your definition of `ancestor` is one or two steps of parentage:
>>
>> > ancestor(A, B) :- parent(A, B).
>> > ancestor(A, B) :-
>> parent(A, C),
>> parent(C, B).
>>
>> I suspect you want one of those lines to appeal to the `ancestor` relation to allow longer chains.
>
> Knowing nothing about datalog he asks naively:
>
> Shouldn't the rule ancestor(A, B) :- parent(A, C), parent(C, B). be applied recursively?
It is — except that there’s no recursion.
> Kevin's definition would work in Prolog.
No it wouldn’t.
Sorry ... brain freeze. Somehow I misread Kevin's code as being
ancestor(A, B) :- parent(A, C), ancestor(C, B).
which would work. You and Sam both are absolutely correct that it
does not work as written.
Apologies for the noise.
George
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