find-key for tables/structs, break inside eachp?

[uvtc]

I see that there's a find-index for arrays/tuples:

(def a [3 5 7 8 1])
(find-index even? a)  #=> 3

But no analogous find-key for maps. I tried this:

(defn find-key
  [pred tbl &opt dflt]
  (var res dflt) # result
  (eachp [k v] tbl
    (when (pred v)
      (set res k)
      (break)))  # <--- Hmm...
  res)

and it worked, but in the process I noticed that break works inside of eachp.

Is this supported behaviour, using break inside something other than a while?

[pepe]

eachp is a macro calling each-template https://github.com/janet-lang/janet/blob/a0ddfcb/src/boot/boot.janet#L432 a function generating the code implemented on top of while.