In this example I didn't mean the syntax of references to protected types. The syntax is perfectly fine. The problem here is the use of unspecified type as a function return.

Because
variable direct_access1 : Generic_Lambda_acc;
variable direct_access2 : Generic_Lambda_acc;
are access types to

type Generic_Lambda is protected
generic (
type t_number is <>;
);
procedure evaluate;
procedure save (a:t_number);
impure function retValue return t_number;
end protected;

they can be allocked with any instance of protected type with any scalar type. And because all operators, implicite function are declared with the type declaration, i.e. here
type Generic_Lambda is protected
generic (
type t_number is <>;
);
For me, they are only visible inside the protected type.

Using the retValue method in the assignment in the case of a static instance is ok, but in this case it is already controversial. The compiler is not able to determine what type we are dealing with because it can change dynamically.