I don't see why that would be necessary. If you want to assign the value of
%t% to
out, but choose a default value (e.g.
"") if it's unset, you can use
out := %t% ?? "". Or perhaps define a function that does that:
Deref(var, default:="") => %var% ?? default. If you don't want to use a default value, then you just push your impending "unset variable" error further down the line:
if
%t% evaluates to
unset, then
out will be unset, and once you try to access it you will get an error (instead of getting it right away with
%t%.