Turbo Prolog

it_is(carnivore) if
positive(does,eat_meat).
it_is(carnivore) if
positive(has,pointed_teeth) and
positive(has,claws) and
positive(has,forward_eyes).
it_is(ungulate) if
it_is(mammal) and
positive(has,hooves).
it_is(ungulate) if
it_is(mammal) and
positive(does,chew_cud).
We can ask questions like
does it have hair?
We want to add corresponding clauses to Turbo Prolog's database so it can reason
with the new clauses. We can add facts to the Turbo Prolog database via the asserta
standard predicate. Thus
asserta(xpositive(has,black_stripes))
will cause
xpositive(has,black_stripes).
to be added to the Turbo Prolog database, provided xpositive has been declared in a
database declaration at the top of the program:
domains
database xpositive(symbol,symbol)
predicates
clauses
Clauses for a predicate declared in a database declaration must not contain any
rules-only facts. For a more detailed discussion of database predicates, see Chapter
II, "Dynamic Databases."
Our database declaration will be as follows:
database xpositive(symbol,symbol)
xnegative(symbol,symbol)
The relationship between xpositive and positive is contained in the first of two rules for
positive:
positive(X,y) if xpositive(X,Y),!.
In other words, xpositive is the database equivalent of positive. We have a similar rule
for negative:
negative(X,y) if xnegative(X,Y),!.
Tutorial VIII: Spreading Your Wings 111