test if a string is a number

Question

How to test if a string is composed only of digits ?

Answer 1

One way is to convert it to an integer and if that fails then you'll know it's not an integer.

is_integer(S) ->
    try
        _ = list_to_integer(S),
        true
    catch error:badarg ->
        false
    end.

Or you can just check all of the digits, but you do have to check the edge case of an empty list:

is_integer("") ->
    false;
is_integer(S) ->
    lists:all(fun (D) -> D >= $0 andalso D =< $9 end, S).