String is it Test
From ErlangCentral Wiki
Testing Whether an Object is a String
You need to test if an object is a string. Since Erlang does not have objects per se, the goal here is really that you want to test if a term is a string.
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.
About the best you can do is determine that the term you are evaluating is a list or not. For that, use the Erlang built-in-function is_list:
1> A="This is fun!". "This is fun!" 2> is_list(A). true 3> B=12. 12 4> is_list(B). false
If you were very concerned that a term was printable, you could verify that it consists of a list of integers that fall within the range of characters you consider to be a string:
1> Fun = fun(XX) -> 1> if XX < 0 -> false; 1> XX > 255 -> false; 1> true -> true 1> end 1> end. #Fun<erl_eval.6.39074546> 2> Is_String = fun(XY) -> 2> case is_list(XY) of 2> false -> false; 2> true -> lists:all(Fun, XY) 2> end 2> end. #Is_String<erl_eval.6.39074546> 3> A. "This is fun!" 4> Is_String(A). true 5> C. [2000,1982,199891] 6> Is_String(C). false