:-[-stdStuff].

% Decision tree program. Implements a simple decision tree expert
% system.  node facts store questions:
%
% node(NodeName,QuestionText,AnswerList)
%
% The AnswerList component describes the child node associated with
% each answer: a(Answer,ChildNode)
%
% To run, enter query: tree(root).

% The root node is the root of the tree.
%
node(root,'How many legs does it have',[a('0',qSwim),a('2',qFeath),a('4',qHoof)]).

node(qSwim,'Can it swim?',[a('Yes',aFish),a('No',aSnake)]).
node(qFeath,'Does it have feathers?',[a('Yes',aBird),a('No',aHuman)]).
node(qHoof,'Does it have hoofs?',[a('Yes',aHorse),a('No',qAtt)]).
node(qAtt,'Does it have an attitude problem?',[a('Yes',aCat),a('No',aDog)]).
node(aCat,'The animal is a cat.',[]).
node(aHorse,'The animal is a horse.',[]).
node(aHuman,'The animal is a human.',[]).
node(aBird,'The animal is a bird.',[]).
node(aFish,'The animal is a fish.',[]).
node(aSnake,'The animal is a snake.',[]).
node(aDog,'The animal is a dog.',[]).

start:-tree(root).
tree(NodeName):-
        node(NodeName,Q,AnsList),
        sOut<<Q<<nl,
        (
                AnsList=[]
                ;
                getAns(AnsList,AnsNode,0),tree(AnsNode)
        ).      

getAns([],AnsNum,HighestNum):-
        repeat,sOut<<"Enter answer number: ",read(AnsNum),
        AnsNum > 0,AnsNum =< HighestNum,nl.
getAns([a(Choice,Node)|More],AnsNode,PrevItem):-
        Item is PrevItem+1,sOut<<Item<<') '<<Choice<<nl,        
        getAns(More,AnsNodeB,Item),
        (
                AnsNodeB=Item,AnsNode=Node
                ;
                AnsNode=AnsNodeB
        ).