Firstly, thanks for your response, much appreciated =).

could you please elaborate? I don't understand the question ...

I'm referring to this %{{f}} code which creates a transient hash (which keys can then operate on) from a hash reference. Perhaps I'm not using the jargon correctly, my apologies.

I don't know of more elegant ways to do this in other languages to be honest. I was hoping that it were possible to create a transient hash more directly with something like  keys %(f) for example.

Creating a helper routine which hides this away or adjusting the f() routine to return a hash reference would both work, but the former sacrifices the brevity I'm after and the latter may not always be feasible.

keys HASH operates on the datatype hash not list, which means something starting with a % sigil here

Do you know if there's a reason that it can't operate on a list?