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yap-6.3/Logtalk/examples/symdiff/plus2.lgt

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:- object(_ + _,
implements(symdiffp)).
:- info([
author is 'Paulo Moura',
version is 1.0,
date is 1999/12/29,
parnames is ['Expression1', 'Expression2'],
comment is 'Symbolic differentiation and simplification of +/2 expressions.',
source is 'Example based on the Clocksin and Mellish Prolog book.']).
diff(Diff) :-
this(X + Y),
once(diff(X, Y, Diff)).
diff(I, J, 0) :-
integer(I),
integer(J).
diff(X, J, DX) :-
integer(J),
X::diff(DX).
diff(I, Y, DY) :-
integer(I),
Y::diff(DY).
diff(X, Y, DX + DY) :-
X::diff(DX),
Y::diff(DY).
simplify(S) :-
this(X + Y),
once(simplify(X, Y, S)).
simplify(I, J, S) :-
integer(I),
integer(J),
S is I + J.
simplify(X, 0, S) :-
X::simplify(S).
simplify(0, Y, S) :-
Y::simplify(S).
simplify(X, J, S + J) :-
integer(J),
X::simplify(S).
simplify(I, Y, I + S) :-
integer(I),
Y::simplify(S).
simplify(X, Y, S) :-
X::simplify(SX),
Y::simplify(SY),
(X + Y \= SX + SY ->
(SX + SY)::simplify(S)
;
S = SX + SY).
:- end_object.