Prolog Programming  

  Translation of a problem into Prolog 

   Facts   
 
   Blood is red   
   Summer is hot   
   Miles is a jazz performer   
 
   red( blood).   
   hot( summer).    
   jazz performer( miles).    

Properties or relationships by    predicates.   
   red, hot  and jazz_performer  are    predicate names 
which denote properties or relations and  
   blood, summer and miles  are    arguments  which
denote individuals, or particular occurences.

   Note :   
 
   Oder of predicates' arguments is arbitrary but MUST be consistent
with our interpretation and maintained throughout.   
 
   son( john, tom).    
 
   son( tom, john).    
 
   Important to decide the order of arguments and then
strictly adhere to this format.

   Lists  :  

days of the week( [mon, tue, wed, thu, fri, sat, sun] ).  

   Order of terms is important .  

   Multiple Ways of Expression   
 
     red( blood).  
     colour( blood, red).  
     property( blood, colour, red)  
 
A predicate is determined by its    name  and    arity  :  
 
   child( ahmed).    
   child( ahmed, peter).    
   child( ahmed, peter, helen).    
 
  Ahmed is a child.
  Ahmed is Peter's child.
  Ahmed is a child of Peter and Helen.

   child/2  : an unambiguous specification of the predicate with
the name    child  nad with two arguments.  
 
Hence :  
 
   child(ahmed, peter).    
   child( [ahmed, peter], helen).    
   child( helen, 2)    

   Tom and Ann are pupils. Dr. Richard is their lecturer and 
Prof. Green is their H-O-D. Relations of this type can be expressed
using a tree.   
 
lecturer( dr_richard, tom).
lecturer( dr_richard, ann).
h_o_d( prof_green, dr_richard).

   RULES   

   A person will buy things if he/she needs them and
he/she can pay their price   
 
buy( Person, Thing) :-
   needs( Person, Thing),
   price( Thing, Price), 
   can_pay( Person, Price).

   Write a Prolog rule for :    
 
A Day is nice if it is sunny and not windy.

   More   

   X will win a boxing match if X will either knock-out
Y or if he/she will get more points than Y   

win_a_boxing_match( X, Y) :-
  knock_out( X,Y) ;
  (points( X, Px),
   points( Y, Py),
   Px > Py).
  
   Write a Prolog rule for :    
 
For all X, Y and Z, X is a grandfather of Y if X is a 
father of Z, and Z is either a father or a mother of Y.

   Lists   

Sequences of k   0 terms, enclosed in square brackets
and seperated by commas.  
 
e.g. []  (empty list) (k = 0)  
 
[1, 2, mary, brother(peter,X)]  
 
Q: lst([1,a,X])  
A: yes  
 
Q: lst([ ])  
A: yes 	
 
Q: compound([1,a,X])  
A: yes  
 
Q: compound([])  
A: no  
 
   List  is a Prolog structure used to represent an
ordered sequence of terms. Also,  
 
([mon,tue,wed,thu,fri,sat,sun])  
 
Elements of a list can be arbitrary Prolog terms  
 
[ dave( 1, date(12, nov 88)),  
  joey( 2, date(15, jul 70)),  
  tomy( 3, date(21, dec 75))]  
 
Elements of a list may also be a list  
 
[ [a,b], [a], [b], [] ]