The 'BASE Attribute

[pvl@cix.compulink.co.uk ("Program Validation L")]

We are confused by the meaning of the 'BASE attribute. For example, the 
LRM states that a fixed point type declaration of the form:

type T is delta D range L .. R;

is, by definition, equivalent to the following declarations:

type fixed_point_type is new predefined_fixed_point_type;
subtype T is fixed_point_type
  range fixed_point_type(L) .. fixed_point_type(R);
  
We would therefore expect T to denote the (implicitly declared) subtype, 
and T'BASE to denote the anonymous type fixed_point_type. This would mean 
that T'DELTA is valid, whilst T'BASE'DELTA is invalid, since P'DELTA is 
only defined for fixed point subtypes.

However, both the Alsys and DEC Ada compilers accept both T'DELTA and 
T'BASE'DELTA, which leads us to suppose our understanding of the LRM is 
incorrect.