CODEWITHSUNDEEP
prolog
whd
whd

Reputation: 1861

How to implement kind of sumator in prolog

I'm trying to implement predicate which will works in mode with all variables not substituted sum(X,Y,Z) will generate all numbers which fill that conditional X+Y=Z. Well actually i can generate list of next numbers in that way.

lisst([_]).
lisst([_|Y]) :- lisst(Y).
fill([]).
fill([0|Xs]) :- fill(Xs).
fill([1|Xs]) :- fill(Xs).
fill([2|Xs]) :- fill(Xs).
fill([3|Xs]) :- fill(Xs).
fill([4|Xs]) :- fill(Xs).
fill([5|Xs]) :- fill(Xs).
fill([6|Xs]) :- fill(Xs).
fill([7|Xs]) :- fill(Xs).
fill([8|Xs]) :- fill(Xs).
fill([9|Xs]) :- fill(Xs).



concat_number(D,N) :- concat_number(D,N,0).
concat_number([],M,M).
concat_number([H|T],N,M) :- M1 is M*10+H, concat_number(T,N,M1).

    sum2(X,Y,Z) :-lisst(X),fill(X),lisst(Y),fill(Y),concat_number(X,X1), concat_number(Y,Y1), Z is X1 + Y1.

and my ask to prolog is ?- sum2(X,Y,Z). but it does not work well only Y number is changing.

Upvotes: 1

Views: 308

Answers (1)

Fred Foo
Fred Foo

Reputation: 363627

The behavior you encounter is due to Prolog's depth-first search control algorithm: because Y has an infinite number of values, Prolog never backtracks beyond the choice point for it. You should implement an iterative deepening search algorithm, like

length(XY, _),       % backtrack over lists in order of length
X=[_|_],             % constrain X and Y to be non-empty
Y=[_|_],
append(X, Y, XY),    % break XY into X and Y
fill(XY),            % fill X and Y in one go
concat_number(X,I),
concat_number(Y,J),
Z is I+J.

Upvotes: 3

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