Why do recurrent modules use an explicit carry rather than making linen variables?

[NeilGirdhar]

This question is more for my understanding, but why do reccurent modules create an explicit carry using the static method initialize_carry rather than Module.variable? Are variable updates not compatible with scan? Or is it just to save the user from having to fish out the final carry from the variables dictionary?

[NeilGirdhar]

Actually, on further thought I can see why module variables aren't the right dataflow for this since they would persist in the state, and it might be a pain to write into them.