Datomic query support

[Matt Bossenbroek]

Have you considered adding support for query variables in a datomic query? Something that could identify unused or mismatched bindings, similar to the support in normal functions.

Currently since all query vars start with a ?, I get no autocomplete either & end up misspelling a lot of them.

Let me know if you’re interested & I could provide some samples of what it could do.

Thanks,

Matt

[Colin Fleming]

Yes, I have, but samples for this would be great, thanks!

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[Matt Bossenbroek]

Awesome - that was quick :)

Here’s an example buggy query:

(d/q '{:find [?barr ?qux]
       :in [$ ?foo]
       :where [[?foo :foo/bar ?bar]
               [?bar :bar/baz ?baz]]}
     db)

We could catch the following:

1) ?barr isn’t present in the query (misspelled)

2) ?qux isn’t there either (made up). Really just all :find vars need to be in the query

3) We’ll get an arity exception because we defined an extra param (?foo) but didn’t provide it.

4) ?baz isn’t used

You could also look for vars provided in the :in clause, but not actually used.

I’m not sure if it would be an error for one of the ?bar’s in the query itself to be misspelled as it would provide a disjoint query. Maybe a simple heuristic that every var must appear more than once - otherwise it could be eliminated. That would catch quite a number of misspellings & semantic errors as well.

Also, datomic has a well defined query grammar. Anything that doesn’t match this could be flagged with an inspection rule: http://docs.datomic.com/query.html#sec-4-2

Thanks!

-Matt

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[Colin Fleming]

One question - how common is it to compose queries from sub-parts in separate data structures?

[Matt Bossenbroek]

I never use it. I always felt like it was too confusing & generated queries that were impossible to profile.

That doesn’t mean that other people don’t though

-Matt

[Matt Bossenbroek]

Oooh - and rename refactoring support :)

Currently it just renames the highlighted symbol.

Thanks!

-Matt

[Timothy Baldridge]

Composing queries on-the-fly is discouraged in Datomic, mostly because the engine will do some amount of query pre-processing and caching, so the proper form is:

(q '[... static query form...]
   db param1 param2 ...)

But some sort of semi-generic system for renaming symbols inside quoted forms seems like a nice-to-have feature. 

Timothy

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[Mark Addleman]

Tossing in a tangential 2 cents:  core.logic macros have a vaguely similar syntax as Datomic queries and suffer from the very similar pain when working with Cursive

[Timothy Baldridge]

Really it's a problem with any macro that defines new symbols. 

(defmacro foo [bindings & body]
  `(let ~bindings ~@body))

(foo [x 42]
  x)

That's valid clojure, but x shows up as undefined in Cursive. 

That's probably the real problem to solve here, some way for users to hint to Cursive that a symbol in a certain position of a form is creating a new symbol that is valid for the body. 

This case is simple since the structure is the same as `let`, but as mentioned core.logic has fresh:

(fresh [x]
  ...)

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[Colin Fleming]

Thanks Timothy, that’s good to know. That makes this easier.

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[Colin Fleming]

Right, Cursive will now let you say “this macro resolves like let” (see here). I’m planning to extend the UI to allow any form to be resolved like any other - currently you can achieve that by hacking config files, but it’s not optimal.

I also have a long-term plan to have an API that will allow anyone to contribute support for these forms, but it’s proving elusive.

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