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ekmett / ersatz

A monad for interfacing with external SAT solvers
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Add queries for relation cardinality #79

Closed emeinhardt closed 11 months ago

emeinhardt commented 11 months ago

Per the title.

jwaldmann commented 11 months ago

Yes, these looks plausible (for the user). Looking at the code, point-free style ((r !) .: (swap .: (,))) feels quite cryptic (I had to look up (.:)). On the other hand, pointed style (what we mostly use) perhaps is too pedestrian.

General thoughts (I should break this out into separate issues)

  1. The name card_dom suggests that this really should be card . dom (where card = sumBits) but then we would need dom : Relation a b -> Set a, for some type Set a that represents unknown sets, which we don't have right now. We could make Set a = Relation a (), then dom r = product r (the-full-relation-from-a-to -()) or similar.

  2. cardinality via sumBits: I am currently experimenting with alternate implementations of at-most-1, at-most-k (improving on Ersatz.Counting). Then (or even before) we could apply at-most-1 for: relation being a function, injectivity of function, and similar.

RyanGlScott commented 11 months ago

I'm leery about adding a new dependency solely for the sake of bringing in the (.:) function. I'd prefer either redefining (.:) in ersatz (its definition is quite small) or writing out the composition explicitly.

emeinhardt commented 11 months ago

@jwaldmann

card_dom / Ersatz.Set?

I see your point about card_dom/card_img and compositionality ± namespace hygiene.

  1. I'll remove those two definitions from this PR.
  2. I am also happy to follow your suggestion about symbolic sets — newtype Set a = Set { unSet :: Relation a () }? — in a new branch to see what that representation looks like with Boolean operations and some functionality for Ersatz.Relation like domain_of_definition/image. Would you like me to open an issue for discussion when that's ready or submit a PR with it?

Functional relations

You allude to functional relations, injectivity, etc.: I have a branch extending Ersatz.Relation that's intended for working with functional relations. Should I wait for your PR with improvements on Ersatz.Counting before submitting my branch as a PR?

Tacit style

The "blackbird" combinator can be useful quite often (more than anything else in composition or similar packages), but yeah I understand tacit style is a matter of taste.

Per above, I've removed card_dom/card_img for now, but I have other PRs currently drafted or in-progress that are written in tacit style in some places (few as point-free as card_dom/card_img!): perhaps after reviewing some of that code it might be clearer what (if any) amount of tacit style is desirable for Ersatz?

@RyanGlScott

composition

I understand wanting to limit additional dependencies, but on the other hand composition itself has no dependencies and is quite stable. Nevertheless, unless you and @jwaldmann would prefer to avoid tacit style entirely, I can make (.:) an Ersatz-local redefinition in the other branches that use it.