Syntax:
pragma Unimplemented_Unit;
If this pragma occurs in a unit that is processed by the compiler, GNAT
aborts with the message xxx not implemented, where
xxx is the name of the current compilation unit. This pragma is
intended to allow the compiler to handle unimplemented library units in
a clean manner.
The abort only happens if code is being generated. Thus you can use specs of unimplemented packages in syntax or semantic checking mode.