Re: Data.Graph transitive closure

If we could boot it out of containers and into its own package, that would make me happier; then I wouldn't have such a weird, special-purpose structure sitting around in an otherwise general-purpose library. On Mon, Jun 24, 2019, 1:38 PM Evan Laforge wrote:

I have been bit before by Data.Graph... I think it's that since it's a type synonym, it inherits Eq from Array, but it doesn't have a normalized form, so Eq is misleading in that topologically equal graphs are not Eq... something like that. And it can't be fixed because it's just a type synonym over Array. That's probably the "no attempt to add abstraction barriers" alluded to above. But the reason I used it in the first place was I wanted a graph, and behold there is Data.Graph already installed. So it's presence in containers gives it the impression of authority, but it's definitely not as well developed as the other types in containers.

Since it seems like it can't be moved or made into a proper type without breaking things, we could at least have some caveats in the documentation, saying what it's appropriate for and what it's not. And maybe warning about that Eq thing. So I guess I'm seconding the "just add documentation" suggestion.

Also while I'm here it's weird and confusing how it silently re-exports Data.Tree...

On Mon, Jun 24, 2019 at 4:02 AM Johannes Waldmann wrote:

...

Hi,

...

I looked at doing this in a "principled" way a long time ago. I then got distracted by something else.....

You don't say :-)

Well, short-term suggestion (for containers:Data.Graph) don't change existing code, but improve documentation and do some benchmarking https://github.com/haskell/containers/issues/648 https://github.com/haskell/containers/issues/649

@David: perhaps you can label these issues as "nice to have" so it does not look like "bugs that need fixing". Benchmarking would make for a nice student project? In fact, I will pitch this to my current class.

- Johannes _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

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