DEPARTMENT OF ARTIFICIAL INTELLIGENCE
                                        
                Prolog exercises - for week beginning 6 Dec 1982


1. The normal method of getting a program into the interpreter, and modifying
   it, is fairly cumbersome for beginners. Devise a better method. You could
   restrict yourself to clauses such as
        fred eats haggis
        ian hates chips
   and other such clauses of the form "Object Relation Object". Your program
   should give you a prompt and allow you to add facts (use built-in predicate
   'assertz(Term)') and ask questions - say of the form
        is it true that fred eats haggis
   Points to remember:
   (a) in ECMI25.UTIL_READIN there is a program for 'read_in(List)' such that
       the goal 'read_in(L)' will give a prompt and wait for you to type. If
       you type
                fred eats haggis
       then L will be instantiated to the list [fred,eats,haggis].
       Experiment with it a bit to get the feel of it.
   (b) there is a built-in operator '=..' such that the goal
       'T =.. [eats,fred,haggis]' will instantiate T to 'eats(fred,haggis)'
       which you can then add (by 'assertz(T)'). Experiment with it a bit to
       get the feel of it.
   (c) You can represent facts in any way you want e.g. as 
       'fact(fred,eats,haggis)' rather than the way suggested by (b) above.
       
2. Embellish your answer in any way you like; try to make it useful for people
   who have seen very little Prolog before. For example, you could try to cope
   with something of the form
        X eats haggis
   by treating it as a question and printing out one (or maybe all) X for which
   it's true. You could add checks so that if someone tries to add the fact
        fred eats haggis
   twice then your program says "I already know that!" at the second go. You
   could try coping with compound constructs such as
        fred eats haggis and fred likes beer
   and even rules such as
        fred likes beer if beer is cheap
   (again, just restrict yourself to things of the form "Object Relation Object
   if Object Relation Object" or whatever you feel you can cope with). Add
   anything you like, such as the power to cope with
        fred likes beer and hates vodka
   - the question is really meant to be an open-ended exercise, and enjoyable.
   If you have trouble with the Prolog for implementing your ideas, bring the
   ideas along so that your tutor and the rest of his group can have a go!