Retrieving a variable's name.

[rodrigo]

How would I go about retrieving a variable's name (not its value)? I
want to write a function that, given a list of variables, returns  a
string with each variable's name and its value, like:

a: 100
b: 200

I get the feeling this is trivial, but I have been unable to find an
answer on my own.

Thanks,

Rodrigo