ITEC 380 2009fall ibarland

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lect09c
prolog intro

% D.Daugherty cover:
% - vars vs constants
% - predicates, not procedures or functions

% Data:

female(alice).
male(bob).
male(charlie).
female(dee).
male(ethan).


% (A) Find dance partners -- one man, one woman:

partner(A,B) :- male(A), female(B).
partner(A,B) :- female(A), male(B).


% Try: 
partner(alice,bob).
partner(bob,alice).
partner(bob,X).
partner(X,bob).
partner(X,Y).


% (B) Find drinking partners -- both with a common preference:

drinks(alice,gin).
drinks(alice,martini).
drinks(bob,soda).
drinks(charlie,soda).
drinks(charlie,whiskey).
drinks(charlie,martini).
drinks(ethan,water).

drinkWith_v1(A,B,Drnk) :- drinks(A,Drnk), drinks(B,Drnk).
%
% Close, but not quite.
% Note that we'll have somebody drinking with themselves.
% Fix with '/==':
drinkWith(A,B,Drnk) :- drinks(A,Drnk), drinks(B,Drnk), A /== B.



% No fundamental difference between facts and rules;
% a fact is just a rule with no variables.
%
drinks(charlie,X).
%
% Charlie should join AA; he drinks anything.
% [Including other people?!]

% It's weird to name a variable which we never use;
% the special variable `_` can be used.
%
drinks(charlie,_).
%
% Underscore is special because even if you mention it
% two or more times, it can match two *different* values:
%
twoNonTeaTotalers(A,B) :- drinkWith(A,_), drinkWith(B,_).
% A and B may not drink the same thing 
% (but they both drink *something*, unlike dee.)

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©2009, Ian Barland, Radford University Last modified 2009.Nov.06 (Fri)

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