Re: Checking to see if a string is a letter

[deuteros <deuteros@xrs.net>]

On Tue 03 Apr 2012 04:26:40a, Simon Wright <simon@pushface.org> wrote in
news:m2k41xi5kv.fsf@pushface.org: 

> deuteros <deuteros@xrs.net> writes:
> 
>> On Tue 03 Apr 2012 01:15:27a, Jeffrey Carter
>> <spam.jrcarter.not@spam.not.acm.org> wrote in
>> news:jle13q$ale$1@tornado.tornevall.net: 
>>
>>> What do you mean by "contains a single letter"?
>>
>> I mean the string contains a single letter and nothing more. For
>> example:
>>
>> a  - Legal
>> A  - Legal
>> aa - Illegal
>> a1 - Illegal
> 
> Then for a start the length of the string needs to be 1.
> 
> If it is, the first (and only!) character needs to be a lower- or
> upper-case letter. There are (at least) three ways of doing this:
> 
> * declare an array of Boolean indexed by Character, with the elements
>   indexed by letters set to True and the others to False, and index by
>   the character to be tested;
> 
> * declare two subtypes of character ("Character range 'a' .. 'z'", for
>   instance) and check whether the character to be tested is 'in' either
>   of the subtypes;
> 
> * use the standard library, Ada.Characters.Handling.Is_Letter (probably
>   the easiest for you!)

Alright, here's my function:

   function isVariable(token: in String) return Boolean is
      ParserException : Exception;
   begin
      if(token'Length = 1) then
         return (Is_Letter(token(1)));
      end if;

      raise ParserException with ("Not a letter : " & token);
     
   end isVariable;

But I'm getting this warning:

warning: index for "token" may assume lower bound of 1
warning: suggested replacement: "token'First + -1"