single valued variables

["SVDSD::PETCHER@ti-eg.CSNET".UUCP]

I am not an Ada expert, so correct me if I'm wrong, but...
When one declares a variable range to be (true..true) is that not in itself a 
contradiction?  A variable that can have only one value is, by definition, not 
a variable, but a constant.  In that context, it seems a compiler should 
create a constant, issue a diagnostic for any subsequent code that attempts to 
change the constant, and generate no executeable code for same.  I realize the 
most likely place for a single-valued variable to occur would be in 
instantiation of a generic, but if a generic so instantiated does not treat 
single-valued variables as constants then the program is basically in error.

Malcolm