Prolog - swi-prolog calc age

Author

swi-prolog calc age

inxdr

2005-02-18, 3:59 am

Hi,
I am teaching prolog to a high school class and today I showed them about
rules as follows.

boy(v).
boy(j).
boy(a).

girl(e).
girl(l).

the rule
possible_boyfriend(A,B) :-
girl(A),
boy(B).

Now one of the students then asked how we could calculate someone's age ...
if we added some facts like
birthday(anna,10/1/1990).

I wonder if people have any ideas how to create a predicate like
age(X,A) :-
A is now() - birthday(X,B). % where A is the person's age
kind regards & thanks in advance
Darren

uwe hunger

2005-02-26, 8:57 am

inxdr wrote:

> Hi,
> I am teaching prolog to a high school class and today I showed them about
> rules as follows.
>
> boy(v).
> boy(j).
> boy(a).
>
> girl(e).
> girl(l).
>
> the rule
> possible_boyfriend(A,B) :-
> girl(A),
> boy(B).
>
> Now one of the students then asked how we could calculate someone's age
> ... if we added some facts like
> birthday(anna,10/1/1990).
>
> I wonder if people have any ideas how to create a predicate like
> age(X,A) :-
> A is now() - birthday(X,B). % where A is the person's age
> kind regards & thanks in advance
> Darren

This was my solution:
/* has birthday this year */
birthday(birthday,5,2,1990).

/* has birthday today, the current system date*/
birthday(birthdaytoday,26,2,1990).

/* hasn't birthday this year */
birthday(nobirthday,3,7,1990).

/* no birth, in planning */
birthday(nosolution,1,1,3000).

age(N,A) :-
get_time(T),
convert_time(T,J,M,D,_,_,_,_),
birthday(N,D1,M1,J1),
compute(A,D,D1,M,M1,J,J1).

compute(A,D,D1,M,M1,J,J1) :-
J =:= J1,
M =< M1,
D =< D1,
A is 0.

compute(A,_,_,M,M1,J,J1) :-
J > J1,
M > M1,
A is J -J1.

compute(A,D,D1,M,M1,J,J1) :-
J > J1,
M =:= M1,
D < D1,
B is J -J1,
A is B - 1.

compute(A,D,D1,M,M1,J,J1) :-
J > J1,
M =:= M1,
D >= D1,
A is J -J1.

compute(A,_,_,M,M1,J,J1) :-
J > J1,
M < M1,
B is J -J1,
A is B -1.

Uwe

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