CSE505 Assignment 3 Problem 2 Solved

Unzip the directory A3_Problem2.zip and refer to the Tiny OOPL program given in tinyoopl.txt – a portion of this file is shown on the next page.   It gives the outline of an object-oriented program consisting of classes, fields, and methods, but without the bodies of methods.  The constructs of a TINY OOPL program can be encoded in three relations:

 

db_class(C1, C2) –  meaning, class C1 extends class C2 

db_field(C, F:T) –  meaning, class C declares field F with type T           

                           (where : is an infix binary constructor) 

db_method(C, M:T1->T2) –  class C declares method M with type T1->T2, where T2 is void                                           when M is a void method  (and -> is an infix binary constructor)

The file database.pl shows instances of these relations for the program in tinyoopl.txt, and a sample from this file reproduced on the next page. Using these relations, define the following Prolog predicates:

 

a.       subclass(C1,C2):  Given C2 as input, return in C1 every subclass of C2, one-by-one upon backtracking.  And, given C1 as input, return in C2 every superclass of C1, one-byone upon backtracking.   Note: the terms superclass and subclass refer not only to the immediate super/subclass, but also the super/subclasses that are obtained transitively.

 

b.      recursive(C):  Given a class C as input, return true/false indicating whether C is recursive, i.e., whether C or one of its subclasses declares a field of type C.  

 

c.       over_ridden(B,C,M,T):  A method M of type T in class C is said to be over-ridden relative a class B if either B or some superclass B2 of B (where B2 is a subclass of C) also defines method M of type T.

 

d.      inherits(C,L):  Given a class C as input, return in L the list of all C2:M:T where M:T is a declared (but not an over-ridden) method of some superclass class C2 of C, and T is M’s declared type.  The predicate should fail if C has no such methods.

 

e.       cycle(C): Return true/false indicating whether there is a cycle through some method of class C.  We say there is a cycle through a method of class C if the method has a parameter with type (class) C or the method has a parameter some other type (class) C2 that declares a method with a parameter  of type (class) C; or, transitively, a class Ck that declares a method with a parameter of type (class) C.  

 

Enter your definitions into the file analyzer.pl.   Load into SWI Prolog the file problem2.pl – which includes database.pl and analyzer.pl.   Proceed as follows.   

%  prolog problem2.pl     % this might vary with platform: Mac, Linux, Windows 

 

?- analyze. 

… prints out banner message …  

     ?- subclass(c, a). 

 ?- why(subclass(c, a)).  % ‘why’ provides an explanation … ?- cycle(a). 

?- why(cycle(a)).    % ‘why’ provides an explanation  

Note:  The why(G) predicate is in the included file explain.pl. Sample test queries and their output are given in the file transcript.