Re: Range types

[Christos Chryssochoidis <C.Chryssochoidis@gmail.com>]

Niklas Holsti wrote:
> 
> Christos Chryssochoidis wrote:
>> Hi,
>>
>> I have a question regarding the range types in Ada. Is there any way 
>> to specify that a type is, say, the values 1..100 and additionally the 
>> values 150..200?
> 
> Brief answer: sorry, no. You cannot leave gaps in the range of numeric 
> types.
> 
> You could define an enumeration type with 151 literals and write a 
> "representation clause" for this type that would force the compiler to 
> use the values 1 .. 100 as the internal representation of the first 100 
> literals and the values 150 .. 200 as the internal representation of the 
> last 51 literals. This would override the the default internal 
> representation that uses the values 0 .. 150 in order. But you could not 
> do direct arithmetic (plus, minus, ...) on such a type because those 
> operations are not predefined for enumeration types.
> 
> Perhaps you could explain why you need a type with a gap?
> 

I would like to define a subtype of Wide_Character for a program that 
processes (unicode) text. This type would represent the Greek letters. 
Greek letters in Unicode, with all their diacritics, are located in two 
separate ranges: 0370 - 03D7 and 1F00 - 1FFF. That's 360 characters to 
write in an enumeration... Since gaps are not allowed in ranges, I 'm 
thinking instead of defining such a type, to define a function that 
would accept a Wide_Character as argument and return a boolean value 
indicating whether the given Wide_Character falls in the ranges of the 
Greek characters.

Thanks very much,

C.C.