Question about scope of def

[yohannd1]

Hello! I was recently trying to implement a while-let macro, and I came across this line in boot.janet (implementation of the if-let macro):

          ~(if (def ,bl ,br) ,(aux (+ 2 i)) ,fal2)

It made me realize that the scope of variables defined in the condition also extends to its body.

As a more... extreme(?) example:

(when (> (def x 1) 0)
  (printf "%j is greater than 0" x))

Is this intended behavior? I found it really good, but I don't quite understand how this has come to happening.

I have found interesting uses for this, though. I'm experimenting using a sort of "iterator" that eventually returns nil when it stops, and I can just throw the def as the condition for a while:

(while (def x (iterator-func))
  (do-something-with x))

[pepe]

Hello! Yes, from my experience, it is an intended behavior I am using in many places. My guess is that both specials are designed and developed this way intentionally. But I am unsure if I have ever discussed it.

[sogaiu]

I don't know if there's a record of this that's easily locatable, but I think we talked about using the return value of def in the context of cond at least once before (^^;