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2-718-281-828
aren't predicates in prolog always starting with a lower letter and only variables with a capital letter?
gorkempacaci
Yes. Also, in the ancestor predicate, the arrow should be in the other direction.
maweki
Yeah, we can't distinguish the arguments. Can't have a parent named X, I guess.
aarroyoc
You can, you just need to quote it in single quotes: 'X'.
dannymi
Just a heads-up to the author:

>Ancestor(X, Y) → Parent(X, Y) ∨ (Parent(X, Z) ∧ Ancestor(Z, Y)).

That's a bug. The arrow needs to go to the left. Also, then, you can also opt to dispense with the disjunction and just use first-order logic normally.

    Ancestor(X, Y) ← Parent(X, Y).
    Ancestor(X, Y) ← Parent(X, Z) ∧ Ancestor(Z, Y).
timClicks
Introductions to Prolog seem to suffer the "draw the rest of the fucking owl" problem. There's a huge gap from the introductory examples to building real projects.

What I would love to see more of is how to embed a prolog interpreter into a wider program, using the source program's data as the database, then prolog (or perhaps datalog) as an advanced query engine or rules engine.

ralphc
Tau Prolog embeds prolog into JavaScript. miniKanren embeds logic programming into Scheme. disclaimer, I haven't used either of these.