====== Animals ======
{{tag>rules interactive}}
===== Description =====
The program uses its identification rules to determine the animal that you have chosen.

**Source**:  PrologTutorial	(on-line tutorial)
===== Download =====
Program source code: {{animals.pl}}
===== Listing =====
<code prolog>
/* prolog tutorial 2.17 Animal identification game.  

    start with ?- go.     */

go :- hypothesize(Animal),
      write('I guess that the animal is: '),
      write(Animal),
      nl,
      undo.

/* hypotheses to be tested */
hypothesize(cheetah)   :- cheetah, !.
hypothesize(tiger)     :- tiger, !.
hypothesize(giraffe)   :- giraffe, !.
hypothesize(zebra)     :- zebra, !.
hypothesize(ostrich)   :- ostrich, !.
hypothesize(penguin)   :- penguin, !.
hypothesize(albatross) :- albatross, !.
hypothesize(unknown).             /* no diagnosis */

/* animal identification rules */
cheetah :- mammal, 
           carnivore, 
           verify(has_tawny_color),
           verify(has_dark_spots).
tiger :- mammal,  
         carnivore,
         verify(has_tawny_color), 
         verify(has_black_stripes).
giraffe :- ungulate, 
           verify(has_long_neck), 
           verify(has_long_legs).
zebra :- ungulate,  
         verify(has_black_stripes).

ostrich :- bird,  
           verify(does_not_fly), 
           verify(has_long_neck).
penguin :- bird, 
           verify(does_not_fly), 
           verify(swims),
           verify(is_black_and_white).
albatross :- bird,
             verify(appears_in_story_Ancient_Mariner),
             verify(flys_well).

/* classification rules */
mammal    :- verify(has_hair), !.
mammal    :- verify(gives_milk).
bird      :- verify(has_feathers), !.
bird      :- verify(flys), 
             verify(lays_eggs).
carnivore :- verify(eats_meat), !.
carnivore :- verify(has_pointed_teeth), 
             verify(has_claws),
             verify(has_forward_eyes).
ungulate :- mammal, 
            verify(has_hooves), !.
ungulate :- mammal, 
            verify(chews_cud).

/* how to ask questions */
ask(Question) :-
    write('Does the animal have the following attribute: '),
    write(Question),
    write('? '),
    read(Response),
    nl,
    ( (Response == yes ; Response == y)
      ->
       assert(yes(Question)) ;
       assert(no(Question)), fail).

:- dynamic yes/1,no/1.

/* How to verify something */
verify(S) :-
   (yes(S) 
    ->
    true ;
    (no(S)
     ->
     fail ;
     ask(S))).

/* undo all yes/no assertions */
undo :- retract(yes(_)),fail. 
undo :- retract(no(_)),fail.
undo.

</code>
===== Comments =====