2026-10-19 helix | Clojure Slack Archive

helix 2026-10-19

lilactown 2026-10-19T15:47:28.852939Z

Watching the latest Rich Hickey talk, I wonder if the new & syntax in :keys/`:keys!` will be either a boon for helping people understand helix’s spread syntax or confusing, since they sort of do the opposite.

seancorfield 2026-10-19T16:28:25.850519Z

Example in Helix? (I ask b/c we're already using 1.13 in production with the new syntax and I'm curious about impacts to libraries etc)

lilactown 2026-10-20T15:38:25.035219Z

I posted this and then afterwards, remembered & is already how dynamic arity functions are defined 😄

lilactown 2026-10-20T15:40:45.743499Z

Helix allows you to merge a dynamic map into a static map like

;; create a new element with props `{:foo 1 :bar 2 :baz 3}`
(let [extra {:bar 2 :baz 3}]
  (d/div {:foo 1 & extra} ...))

The macros (`$` and all the dom element constructors) emit code to efficiently construct a JS object of the static props and then dynamically merge in the additional map passed to the & key.

lilactown 2026-10-20T15:41:28.408969Z

it’s sort of a mirror of the rest params/new keys functionality

seancorfield 2026-10-20T16:10:44.609199Z

1.13 makes & invalid as a destructuring key, so maybe that will affect you?

seancorfield 2026-10-20T16:13:55.760609Z

A search of the Helix code suggests you don't use it that way, so I think you'll be fine.

dominicm 2026-10-20T21:12:17.902689Z

Main thing is probably that :& is built in to destructuring somehow

seancorfield 2026-10-20T21:13:41.089509Z

Not :&, just &. {:keys! [a b & :c]} -- checks and binds :a to a and :b to b, and also checks :c (with no binding).

seancorfield 2026-10-20T21:16:28.427249Z

Prior to 1.13, if you had :& as a key and used {:keys [a b & :c]} you'd get four bindings:

> clj -M:1.12
Clojure 1.12.6
user=> (let [{:keys [a b & :c]} {:a 1 :b 2 :c 3 :& 4}] [a b & c])
[1 2 4 3]
user=>

> clj -M:1.13
Clojure 1.13.0-alpha9
user=> (let [{:keys [a b & :c]} {:a 1 :b 2 :c 3 :& 4}] [a b & c])
Syntax error compiling at (REPL:1:1).
Unable to resolve symbol: & in this context
user=>

lilactown 2026-10-21T15:58:40.795759Z

yeah i don’t imagine this will break anything, I was more pondering about extending the meaning of the & symbol to another place

lilactown 2026-10-21T15:59:01.984679Z

it’s probably neither here nor there

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helix 2026-10-19