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There's plenty of reason: you can put any code you like inside of `with-read-txn`, including closures that are evaluated lazily. If you dislike the duplication
by prospero 10y ago
There's plenty of reason: you can put any code you like inside of `with-read-txn`, including closures that are evaluated lazily. If you dislike the duplication, create a syntactic form that allows less, like this:
(transaction-> db-name
(put! ...)
...)
This doesn't lend itself to every kind of action, but it is narrower. Alternately, create a variadic version of `put!` which guarantees eager evaluation inside of a transaction.
The nightmare scenario here is not that the sequence will lazily evaluate outside of `with-read-txn`, because that at least will throw an error. Rather, it's that it will be evaluated inside a different transaction, without anyone ever realizing it. By leaving that possibility open, you're doing a huge disservice to the users of your library.
- shriphani 10y agoOk I see your point. I am curious how that would happen though - essentially you'll need to bind the txn to a different transaction from the one intended and the whole thing locks up. I am curious how to guarantee eager evaluation - dorun, doall and run! are all sequence-oriented right?
- prospero 10y agoIt's not that hard to imagine: map a `get` over a series of keys inside a transaction, return that lazy sequence, and use the results to do another series of operations within a different transaction. Libraries typically can't guarantee eager evaluation, since that's a property of the top-level execution. That's why libraries shouldn't use `binding`.
- shriphani 10y agoWow I am not sure how I missed that - thanks for pointing it out. The (transaction-> ###) pattern looks a lot nicer to me. Really appreciate the help.
- shriphani 10y agoFunnily enough, I think I picked up this habit from Korma source: https://github.com/korma/Korma/blob/master/src/korma/db.clj#L299 https://github.com/korma/Korma/blob/master/src/korma/db.clj#...