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by zozbot234 1278 days ago
> This all looks very mind-bending to me (in a good way). Perhaps Verse will one day be as influential for PL design as Haskell has been.

I'm not convinced. Making non-determinism a first-class feature in the language might be good if you simply care about logical specifications that might enable you to prove something correct, but a real-world program implementation has to make heuristic choices for efficiency as to when to evaluate what (and perhaps where, especially in a parallel/distributed setting), and just stating that evaluation is "lenient" isn't really saying anything worthwhile. So this kind of design choice will ultimately be expressed with ugly hacks, as with e.g. Prolog where the 'cut' feature is used to override the default search strategy.
1 comments
FullyFunctional 1278 days ago
But it's very much not non-deterministic. It's a deterministic choice. You can give it an exact semantics.
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cryptonector 1278 days ago
Correct, but "non-determinism" is a misnomer used in programming language theory to refer to generators and pervasive backtracking. Prolog, Icon, jq, etc. -- all fully deterministic, but known as non-deterministic owing to the pervasive generators and backtracking.
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imtringued 1278 days ago
It is not a misnomer. You can use generators and backtracking to simulate non determinism. That means the simulator plus non deterministic algorithm are deterministic but the algorithm is not.
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cryptonector 1277 days ago
The idea in Prolog and such is that you write "goal-seeking code" and it "magically" obtains the correct answer by brute force but without the brute force being syntactically/lexically apparent. But it's still brute force. It's a catchy name, but it's not accurate. It might be more accurate if "simulation" were part of the name.
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FullyFunctional 1277 days ago
As presented in the slides it's obvious that it's a generator-paradigm, thus like Icon etc. It's really just a way of making iterators very fundamental in the language. It's deterministic and you are assume to understand that. The "PROLOG style goal searching" is probably less relevant here.
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zozbot234 1278 days ago
How? The slide deck calls it a "lenient" evaluation order, and doesn't really say how to make an explicit choice of what cases should be tried first. So it seems to have all the same problems as naïve Prolog.
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disconcision 1278 days ago
exact semantics are given here: https://simon.peytonjones.org/assets/pdfs/verse-conf.pdf. runtime efficiency isn't specifically addressed afaict
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