Can I define variables using other variables (or expression language)?

[Krzysztof Zarzycki]

Hi community,
I'm using Nifi Variable Registry (through UI). I would like to define one
variable using value from other variable, like:
env = staging
scratch_path=/${env}/scratch

I tried exactly that approach, but it didn't work, the variable
scratch_path gets value literally /${env}/scratch.

Do you know if it should or should not be possible? Maybe it's a good idea
for a feature request?

Thanks,
Krzysztof