Program Simplification: Example

• Original program

  plus(X,Y,Z):-
       int(X),int(Y),!,Z is X + Y.
  plus(X,Y,Z):-
       int(Y),int(Z),!,X is Z - Y.
  plus(X,Y,Z):-
       int(X),int(Z),!,Y is Z - X.

• If this program is to be used for call plus(X,Y,Z) and analysis is able to determine that X and Y are integers, we can simplify it to:

  plus(X,Y,Z):-
       Z is X + Y.

• int(X) and int(Y) are redundant tests
• Cut (!) is used by the simplifier to eliminate the two other clauses of plus/3
• If plus/3 is called at some other program point and the analyzer has not determined that X and Y are integers, the previous simplification cannot be done.
• It can be solved using multiple specialization.