prolog program predicate

[sperelli]

Hi everybody,

I just start to learn Prolog.
I have to write a Prolog program where the Horn clauses and the goal will only consist of a predicate symbol, which thus will not be followed by a sequence of terms enclosed in parentheses.

What exactly means?
Something like this:

A :- B, C, D.
B.
C.
D :- E.
E.

and the goal A or another character.
Is it right? Someone can give me another example?

 

[joel76]

That's correct but you must use lowercase letters :

a :- b, c, d.
b.
c.
d :- e.
e.

 

[joel76]

Notice that b, c and e are called "facts

 

[sperelli]

Thanks a lot!!!
and what exactly means that code?

that 'a' is true only if 'b' , 'c' and 'd' are true? right?

and the goal could be every letter that i use in the code?

 

[joel76]

You should say "a succeeds only if b, c and d (so e) succeed".
Since b, c and e are facts, a succeeds.
Yes, every letter in this example can be a goal.

 

[sperelli]

Thanks a lot!!!

I have a last question.. I have to write in C the and/or tree for this prolog file..
How can I do it? how I know when is an 'or' and when is an 'and'.

For example.. if the goal is 'a':

a
|
--------------------------
| | |
b c d
| | |
succeed succeed e
|
succeed

is it ok? but how i can make an 'or'? and to have a 'failure'?

 

[joel76]

'or' is achieved with a semicolon ';'.
If I understand your question 'to have a failure' you can use \+ wich is the negation
\+a. gives 'false'