[Enhancement]: multi-arity subscription sugar

[dhleong]

What do you suggest?

re-frame currently supports the :<- [...] sugar syntax in reg-sub to perform a literal (subscribe) as an input signal (we could call this 1-arity) and :-> fn and :=> fn to provide a 1-arity or multi-arity computation fn, respectively.

Frequently, I find myself wanting to chain multi-arity subscriptions such that, for example:

; EG: I have an ID I specifically want to reference:
(<sub [:my-sub id])

; *or* EG: I want to reference some shared "current" ID:
(<sub [:my-sub])

Perhaps this is an anti-pattern, but it has felt like a natural way to do things, and for simple subscriptions can work well with the :=> sugar.

However, if I want to use that multi-arity subscription as input to another subscription, I start to get in trouble:

; This doesn't work because it only subscribes to the 1-arity version
(reg-sub
  :dependent-sub
  :<- [:my-sub]
  :-> computation)

; Instead, I have to do:
(reg-sub
  :dependent-sub
  (fn [[_ id]]
    (subscribe [:my-sub id])
  :-> computation)

What if, instead, we could write this as:

(reg-sub
  :dependent-sub
  :<= [:my-sub]
  :-> computation)

and have the query-vector "params" conj'd into the provided subscription vector, similar to how :=> works on the computation side? Is this a terrible idea?