differentiate a string from a list in Erlang

Question

In Erlang when you have a list of printable characters, its a string, but a string is also a list of items and all functions of a list can be applied onto a string. Really,

Answer 1

You have two functions in the module io_lib which can be helpful: io_lib:printable_list/1 and io_lib:printable_unicode_list/1 which test if the argument is a list of printable latin1 or unicode characters respectively.

Answer 2

using the isprint(3) definition of printable characters --

isprint(X) when X >= 32, X < 127 -> true;
isprint(_) -> false.

is_string(List) when is_list(List) -> lists:all(fun isprint/1, List);
is_string(_) -> false.

you won't be able to use it as a guard, though.