fnk binding form can't combine optional parameters with destructuring

Question

fnk binding form can't combine optional parameters with destructuring

vilmibm opened this issue 9 years ago · comments

When defining a fnk, I'd hope to be able to do something like this:

((fnk [{[:sub foo] 1} bar] (+ foo bar)) {:sub {:bar 1}})

to get back 2. Unfortunately, combining the optional {} syntax with the [] destructuring syntax does not work:

CompilerException java.lang.ClassCastException: clojure.lang.PersistentVector cannot be cast to clojure.lang.Named, compiling:(*cider-repl trapperkeeper*:16:32)

Nate Smith commented 9 years ago

👍

Jason Wolfe · Answer 1 · Tue Jan 12 2016 05:09:43 GMT+0800 (China Standard Time)

Thanks for the report. This is currently by design -- I don't see an easy way to provide a default in the case that the sub-form binds more than one symbol, and the semantics of what's required vs. optional isn't exactly clear (does this mean that :sub is optional, but if present must contain a foo?).

Given the complexities, we've felt that in such cases, we're probably better just using what Clojure provides already. But if you have a concrete proposal for how you'd like this to work that covers all the cases, we'd be happy to consider it.

Nate Smith · Answer 2 · Fri Jan 15 2016 07:00:58 GMT+0800 (China Standard Time)

@w01fe Thanks for the speedy reply. I wondered if this was the case.

I'd be happy to write up a proposal / work on implementing it if y'all approved.

I'm getting over a headcold (hence my delayed response) but I'll try to get to that proposal soon.

Jason Wolfe · Answer 3 · Fri Jan 15 2016 07:11:30 GMT+0800 (China Standard Time)

Sounds good, thanks for the offer! If you can prepare something along the lines of the "fnk syntax proposal" here: https://github.com/plumatic/plumbing/tree/master/src/plumbing/fnk that covers all the cases that would be ideal, and we can review and take things from there. Cheers!