You can't! An Erlang string is just a list of characters (really,
a list of integer values). So, the variable you are examining could be a list of letters, a set of coordinates, or a set of bytecode for Donald Knuth's MMIX machine.
You could determine that a term holds a list of integers that fall within the range of characters you consider to be a string:
-- GordonWeakliem - 05 Apr 2004
The Python Cookbook discusses how simplay asking isinstance is "UnPythonic" and has a discussion on "duck typing", in that their solution just asks if you can concatenate a string to an unknown object. I'm not sure how to address this. You could literally ask if (string-append an-object "") works w/o throwing an exception, but would anyone do this?