I have a variable a that is defined:
a = 1
I can check whether a is defined
@isdefined a # true
Some other variables may or not be defined at this point in the program:
@isdefined b # false
However, I only have available a vector of symbols [:a, :b] and I want to check whether
the corresponding variables a and b are defined.
This does not help:
@isdefined :b # true
How can I find whether the variable b is defined if I only have the
corresponding symbol :b available?