Multiple Specialization: Example

• Original program:

  map_add1(_,[]).
  map_add1(X,[Y|TY]):-
       ( nonvar(X) -> Y is X+1, map_add1(X,TY)
                   ;  X is Y-1, map_add1(X,TY) ).

• Multiply specialized program:

  map_add1(_,[]).
  map_add1(X,[Y|TY]):-
       ( nonvar(X)-> Y is X+1, map_add1_nv(X,TY)
                  ;  X is Y-1, map_add1(X,TY) ).
   
  map_add1_nvX(_,[]).
  map_add1_nvX(X,[Y|TY]):-
       Y is X+1, map_add1_nvX(X,TY).

• Analysis has generated two versions for map_add1.
• They allow further optimizations.
• Otherwise they would be collapsed in the same version (minimization).
• Invariant extracted from cycle.
• Optimized version calls itself recursively.