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This works to find all combinations of integers >= 0 whose sum is 3. :- use_module(library(clpz)). % for ins, #=, and label
:- use_module(library(format)).
demo :-
[A, B, C] ins 0..sup,
A + B + C #= 3,
label([A, B, C]),
format("~d + ~d + ~d = 3~n", [A, B, C]).This code is very similar, but does not work. :- use_module(library(clpz)). % for ins, #=, and label
:- use_module(library(format)).
demo2 :-
[A, B, C] ins -6..6,
A * B * C #= -6,
label([A, B, C]),
format("~d * ~d * ~d = -6~n", [A, B, C]).The output from this code is the following rather than giving specific values: |
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Replies: 2 comments 6 replies
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Same with Shorter: While this answer is not incorrect, all the additional constraints are no longer needed. In general, whenever you try out constraints, it helps to just stick to the top level. It will print out everything for you. |
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Well spotted, thank you a lot for reporting this! I have filed #1938 to address this, please have a look. Other than that, @UWN has already raised an important point: The toplevel reports results for you, you can simply press |
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I tested the pull request from @triska after it was merged and it works great! |
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As an example, so that you can remove side-effects from the program, we can write: demo(A*B*C = -6) :-
Vs = [A,B,C],
Vs ins -6..6,
A*B*C #= -6,
label(Vs).
Yielding: ?- demo(T). T = (-6* -1* -1= -6) ; T = (-6*1*1= -6) ; T = (-3* -2* -1= -6) ; T = (-3* -1* -2= -6) ; ... . Such answers can be easily tested and reasoned about. Further, programs without side-effects can be run with any execution strategy, a major attraction of Prolog. |
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This is brilliant! I would have never thought to write it this way. |
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To benefit most from Prolog, you must keep to its pure monotonic core. Side-effects and extra-logical predicates are well outside this core. Try to think in terms of relations and state what you want to describe, using only the predicates from the pure core. A small number of predicates suffices to express a great number of programs in this way. As a guidance, the enumeration of libraries at https://github.com/mthom/scryer-prolog/ is ordered roughly in proportion of their expected need when keeping to the pure monotonic core, with |
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You stated that so well and I feel I need to be constantly reminded of this. I hope you don't mind, but I added a section titled "Pure Monotonic Core" to my blog page that quotes this and credits you. Please let me know if you would rather I remove it or reword it in some way. |
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See this for a more complete definition. |
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As an example, so that you can remove side-effects from the program, we can write:
demo(A*B*C = -6) :- Vs = [A,B,C], Vs ins -6..6, A*B*C #= -6, label(Vs).Yielding:
Such answers can be easily tested and reasoned about. Further, programs without side-effects can be run with any execution strategy, a major attraction of Prolog.