Question

Need help with this Prolog question..

1. Given facts such as
Bob is taller than Mike.

Mike is taller than Jim


Jim is taller than George


Write a recursive program that will determine that Bob's height is greater than George's.

Answer 1

First you want to list your facts as your knowledge base:
```
taller(bob, mike).
taller(mike, jim).
taller(jim, george).
```

Then you make taller a transitive predicate.
```
taller(X,Y) :-
taller(X,Z),
taller(Z,Y).
```

Finally you would query.
```
?- taller(bob, george).
```

It's been a long time since I've done prolog, but this is my best guess. I don't feel like getting an interpreter and there any any easy ones online.

Answer 2

So what will likely happen when you make the query:
1. It won't find `taller(bob, george)` anywhere and will resort to using `taller(X,Y)`
2. `taller(X,Z)` will iterate through `taller(bob, Z)`, starting at `Z=mike`.
3. This will be plugged into `taller(Z, george)`, resulting in `taller(mike, george)`.
4. Since it isn't in the knowledge base, it will resolve this rule using 'taller(X, Y)` again.
5. It will keep recursing through, eventually hitting `taller(jim, george)`, which will result in true.

Answer 3

Here is how I think stuff would translate into a procedural language:
```
function taller(X, Y) {
if (X == bob && Y = mike) return true; // taller(bob,mike)
if (X == mike && Y = jim) return true; // taller(mike,jim)
if (X == jim && Y = george) return true; // taller(jim, george)

// taller(X,Y) :-
for (Z in [mike]) { // taller(X,Z)
return taller(Z, Y); // taller(Z,Y) this is where the recursion happens
}
}

```
Though, I am just not completely sure.

Answer 4

Thank you!