I have this piece of homework that I have to write in Prolog.The requirement is to write a piece of code that does binary addition such as:
?- add([1,0,1],[1,1],X).
X = [0,0,0,1]
And so, this is the code that I came up with:
add([],[], _).
add([],Y, Z) :- append([], Y, Z).
add(X,[], Z) :- append(X,[],Z).
add([HX|TX],[HY|TY], Z) :-
HX = 1,
HY = 1,
add(TX,TY, Z1),
add([1],Z1, Z2),
append([0],Z2,Z),!.
add([HX|TX],[HY,TY], Z) :-
HX = 0,
HY = 1,
add(TX,TY,Z1),
append([1],Z1, Z),!.
add([HX|TX],[HY|TY], Z) :-
HX = 1,
HY = 0,
add(TX,TY,Z1),
append([1],Z1, Z),!.
add([HX|TX],[HY,TY], Z) :-
HX = 0,
HY = 0,
add(TX,TY,Z1),
append([0],Z1, Z),!.
It seems to do what I needed, however, there are strange issues with it that I can not understand, so if someone could guide me to what I have done wrong, I would be glad.
Results:
?- add([1,1,1,1], [1,1],Z).
Z = [0, 1, 0, 0, 1]. % this is correct
?- add([1], [1],Z).
Z = [0, 1]. % this is correct
?- add([1,1,0,1], [1,1],Z).
Z = [0, 1, 1, 1]. % this is correct
?- add([1],[0],Y).
Y = [1|_G7100]. % there is an error here, but its not the big issue.
?- add([1,0,1], [1,1],Z).
false. % no results are returned.
104 ?- add([0], [1],Z).
false. % no results returned either
Problem: Whenever there seems to be a 0 in the first binary list, under some conditions(still trying to figure them out), no results seems to be returned.but I can't seem to locate my error.Would be glad if someone can tell me what I did wrong.
There are 3 mistakes:
add([],[],[]). instead of add([],[], _).. This fails for equal-length lists.add([HX|TX],[HY|TY], Z) instead of add([HX|TX],[HY,TY], Z). This fails when the second list (Y) contains less than two elements.Fix these and your code should run well: see here.