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Prolog feels like magic, and it well worth learning. It is a general purpose programming language rather than a very specific purpose tool like Z3. Sadly non-'

Prolog feels like magic, and it well worth learning. It is a general purpose programming language rather than a very specific purpose tool like Z3. Sadly non-'pure' logical programming is required to get real-world performance (eg. cuts that prune the search tree) which kind of feel like, or is, a leaky abstraction that breaks the magic. I have had good success in solving logical problems by asking o1 to produce prolog programs.

coliveira 2y ago
If you learn modern prolog techniques, cuts have become less and less necessary.
- sriram_malhar 2y ago
  Can you point to some resources that show this? Are there new facilities that make cuts fewer? Are there more accepted idiomatic ways published for different kinds of problems? I learnt Prolog a long time ago and would like to start from scratch.
  - coliveira 2y ago
    There is a web site that shows how to use modern techniques to make Prolog less procedural: https://www.metalevel.at/prolog https://www.metalevel.at/prolog
xlii 2y ago
> Sadly non-'pure' logical programming is required to get real-world performance (eg. cuts that prune the search tree) which kind of feel like, or is, a leaky abstraction that breaks the magic. They aren’t required but are convenient. Excuse brutalizing syntax and formatting but in Prolog you can do: A(X) :- between(1,3,X). B(X) :- between(1,1000,X). ?- A(X), B(X). ?- B(X), A(X). And get either 9 visits or 3000. It’s possible to design a program without cuts but (in my opinion) it’s very hard and doesn’t bring any benefits outside of street cred. Also cuts and pruning long time ago felt like bloated terms (when I didn’t get Prolog) whereas it’s a simple break equivalent in imperative languages loops.
johnisgood 2y ago
I have solved some logic problems using Prolog, but Prolog is neat for text-based adventure games, too. SWI Prolog has great libraries, BTW.
lproven 2y ago
I wonder if it is still the case that the most widely-used Prolog app in the world was the solver for network stack configurations in Windows NT? https://web.archive.org/web/20040603192757/research.microsoft.com/research/dtg/davidhov/pap.htm https://web.archive.org/web/20040603192757/research.microsof...
YeGoblynQueenne 2y ago
There's nothing wrong with the cut, or with getting more control over the execution of your program, which is what the cut gives you. You only get in trouble with the cut when you're just starting out and don't know what you're doing, and write your code in a way that it keeps entering infinite recursion or backtracking until the cows come home. At that point, because you don't yet know how to control those behaviours, you start sowing your code with cuts all over the place, which maybe stops the backtracking and infinite recursion (but maybe not) but it makes it an incomprehensible mess that still doesn't do what you want it to do. As you grow and learn, you figure out how to control backtracking and recursion by ordering your program clauses and your clause literals in a sensible manner. At that point the use of the cut becomes so regular and formulaic that it might as well be added in by a pre-procesor. For instance, you want a program that walks over a list and modifies an element if a condition holds, otherwise it continues, until the list is empty. You write: % Program "skeleton" not meant to be executed but to expose a pattern modify_list([],Xs,Xs):- ! % We're done, stop trying modify_list([X|Xs],[Y|Acc],Bind):- modify_element(X,Y) ,! Don't re-process X! ,modify_list(Xs,Acc,Bind). modify_list([_X|Xs],Acc,Bind):- modify_list(Xs,Acc,Bind). In the example above, the two cuts have a very clear reason to be where they are (they stop unnecessary backtracking) which is immediately obvious by eyballing the program with sufficient experience. The vast majority of the use of cuts in the code you write once you have a bit of experience and understanding of how Prolog works is like that.

coliveira 2y ago

If you learn modern prolog techniques, cuts have become less and less necessary.

sriram_malhar 2y ago
Can you point to some resources that show this? Are there new facilities that make cuts fewer? Are there more accepted idiomatic ways published for different kinds of problems? I learnt Prolog a long time ago and would like to start from scratch.
- coliveira 2y ago
  There is a web site that shows how to use modern techniques to make Prolog less procedural: https://www.metalevel.at/prolog https://www.metalevel.at/prolog

xlii 2y ago

> Sadly non-'pure' logical programming is required to get real-world performance (eg. cuts that prune the search tree) which kind of feel like, or is, a leaky abstraction that breaks the magic. They aren’t required but are convenient. Excuse brutalizing syntax and formatting but in Prolog you can do: A(X) :- between(1,3,X). B(X) :- between(1,1000,X). ?- A(X), B(X). ?- B(X), A(X). And get either 9 visits or 3000. It’s possible to design a program without cuts but (in my opinion) it’s very hard and doesn’t bring any benefits outside of street cred. Also cuts and pruning long time ago felt like bloated terms (when I didn’t get Prolog) whereas it’s a simple break equivalent in imperative languages loops.

johnisgood 2y ago

I have solved some logic problems using Prolog, but Prolog is neat for text-based adventure games, too. SWI Prolog has great libraries, BTW.

lproven 2y ago

I wonder if it is still the case that the most widely-used Prolog app in the world was the solver for network stack configurations in Windows NT? https://web.archive.org/web/20040603192757/research.microsoft.com/research/dtg/davidhov/pap.htm https://web.archive.org/web/20040603192757/research.microsof...

YeGoblynQueenne 2y ago

There's nothing wrong with the cut, or with getting more control over the execution of your program, which is what the cut gives you. You only get in trouble with the cut when you're just starting out and don't know what you're doing, and write your code in a way that it keeps entering infinite recursion or backtracking until the cows come home. At that point, because you don't yet know how to control those behaviours, you start sowing your code with cuts all over the place, which maybe stops the backtracking and infinite recursion (but maybe not) but it makes it an incomprehensible mess that still doesn't do what you want it to do. As you grow and learn, you figure out how to control backtracking and recursion by ordering your program clauses and your clause literals in a sensible manner. At that point the use of the cut becomes so regular and formulaic that it might as well be added in by a pre-procesor. For instance, you want a program that walks over a list and modifies an element if a condition holds, otherwise it continues, until the list is empty. You write: % Program "skeleton" not meant to be executed but to expose a pattern modify_list([],Xs,Xs):- ! % We're done, stop trying modify_list([X|Xs],[Y|Acc],Bind):- modify_element(X,Y) ,! Don't re-process X! ,modify_list(Xs,Acc,Bind). modify_list([_X|Xs],Acc,Bind):- modify_list(Xs,Acc,Bind). In the example above, the two cuts have a very clear reason to be where they are (they stop unnecessary backtracking) which is immediately obvious by eyballing the program with sufficient experience. The vast majority of the use of cuts in the code you write once you have a bit of experience and understanding of how Prolog works is like that.