3 ms·

I love pure Prolog, and I welcome new developments like the pure if_/3 discussed below. But at the same time, your position is needlessly extremist. It's perfec

I love pure Prolog, and I welcome new developments like the pure if_/3 discussed below. But at the same time, your position is needlessly extremist. It's perfectly fine to write a program in 90% pure Prolog and 10% in its "quirky imperative" subset. Depending on what you're doing, turning that ratio around to 20-80 can still be useful: "quirky imperative" Prolog is still the best language for matching and transforming tree-shaped data that I know of. The ability to mix in impure features where needed is what makes Prolog practical.

OskarS 7y ago
Very well said, exactly my opinion as well.
superdisk 7y ago
The problem is, once you introduce a non-logical predicate, everything in the call stack "above" it is tainted and rendered non-logical. Since you frequently have to resort to using (\+)/1 almost as a necessity, the codebase ends up being 90% illogical and 10% logical. And at that point you step back and ask why you're even using prolog. However: I do miss DCGs in every other language I've used. They're so useful that I've come to hate using regexes or even worse: manually parsing lists and strings.
- tom_mellior 7y ago
  > The problem is, once you introduce a non-logical predicate, everything in the call stack "above" it is tainted and rendered non-logical. That's a very general statement. The non-logical behavior can be well-contained and unobservable from the outside. For example, the nice and pure if_/3 internally uses both of the non-logical predicates (->)/2 and (==)/2. Yet viewed from the outside it doesn't taint anything. > And at that point you step back and ask why you're even using prolog. As I wrote above, because I think even used imperatively it's a very convenient language for expressing matching and transformation of trees. And DCGs are great as well, I agree.

3 ms·

I love pure Prolog, and I welcome new developments like the pure if_/3 discussed below. But at the same time, your position is needlessly extremist. It's perfec

by tom_mellior 7y ago

OskarS 7y ago
Very well said, exactly my opinion as well.
superdisk 7y ago
The problem is, once you introduce a non-logical predicate, everything in the call stack "above" it is tainted and rendered non-logical. Since you frequently have to resort to using (\+)/1 almost as a necessity, the codebase ends up being 90% illogical and 10% logical. And at that point you step back and ask why you're even using prolog. However: I do miss DCGs in every other language I've used. They're so useful that I've come to hate using regexes or even worse: manually parsing lists and strings.
- tom_mellior 7y ago
  > The problem is, once you introduce a non-logical predicate, everything in the call stack "above" it is tainted and rendered non-logical. That's a very general statement. The non-logical behavior can be well-contained and unobservable from the outside. For example, the nice and pure if_/3 internally uses both of the non-logical predicates (->)/2 and (==)/2. Yet viewed from the outside it doesn't taint anything. > And at that point you step back and ask why you're even using prolog. As I wrote above, because I think even used imperatively it's a very convenient language for expressing matching and transformation of trees. And DCGs are great as well, I agree.