There are two issues involved. How to get the variable name X into the system, and how to get a term with such a variable into the atom. The X you type in is read by the top level which converts it to a regular variable which does not have a name associated. Let’s see … Read more
Also, not sure why you’re dead against cuts, so long as their removal would not change the declaritive meaning of the code, as per your link. For example: inter([], _, []). inter([H1|T1], L2, [H1|Res]) :- member(H1, L2), inter(T1, L2, Res). inter([_|T1], L2, Res) :- inter(T1, L2, Res). test(X):- inter([1,3,5,2,4], [6,1,2], X), !. test(X). X = … Read more
For elegance and didactic reasons alone, dif/2 is clearly preferable here and also in the vast majority of other cases, since as you already note “a lot of unnecessary unifications might take place” otherwise, and also because dif/2 is a pure and nicely declarative predicate that can be used in all directions and at any … Read more
The following is based on my previous answer to “Remove duplicates in list (Prolog)” and on this previous answer to the question “Prolog union for A U B U C“. list_item_subtracted_count0_count/5 is derived from list_item_subtracted/3. list_counts/2 is derived from list_setB/2, which were both defined here. list_item_subtracted_count0_count([], _, [], N,N). list_item_subtracted_count0_count([A|As], E, Bs1, N0,N) :- if_(A … Read more
What is the idiomatic approach to this class of problems? Is there a way to simplify the problem? Many of the following remarks could be added to many programs here on SO. Imperative names Every time, you write an imperative name for something that is a relation you will reduce your understanding of relations. Not … Read more
Use CLP(FD) constraints, for example: :- use_module(library(clpfd)). binary_number(Bs0, N) :- reverse(Bs0, Bs), foldl(binary_number_, Bs, 0-0, _-N). binary_number_(B, I0-N0, I-N) :- B in 0..1, N #= N0 + B*2^I0, I #= I0 + 1. Example queries: ?- binary_number([1,0,1], N). N = 5. ?- binary_number(Bs, 5). Bs = [1, 0, 1] . ?- binary_number(Bs, N). Bs = … Read more
The recursive part is not quite correct. split([], [], []). split([Head|Tail], [Head|List1], List2) :- Head>=0, split(Tail, List1, List2). split([Head|Tail], List1, [Head|List2]) :- Head<0, split(Tail, List1, List2). The Head should be added to the positive list if Head >= 0 and to the negative list when Head < 0. Moreover, checking the sign of Head at … Read more
shuffle([], B, B). shuffle([H|A], B, [H|S]) :- shuffle(B, A, S). In this kind of problems, usually the difficult part is not Prolog but identifying the simplest recursive relation that solves it.
Those prefix operators, in this context, represent instantiation modes, i.e. they tell you which arguments should be variables or instantiated when calling the predicate. They also tell you if an argument will be (possibly further) instantiated by the call. They can also be used to tell you that an argument is going to be meta-interpreted … Read more
You can take a look at Yield Prolog. Yield Prolog uses yield keyword in C# (and Python, and JavaScript) and custom Variable class to simulate Prolog machine. This way, you get a Prolog API in your favourite language. You don’t need to connect your main language with P# or similiar projects.