GNAT Exceptions g-except ads (GNAT Reference Manual)

### 12.69 `GNAT.Exceptions` (`g-except.ads`) ¶

Normally it is not possible to raise an exception with a message from a subprogram in a pure package, since the necessary types and subprograms are in `Ada.Exceptions` which is not a pure unit. `GNAT.Exceptions` provides a facility for getting around this limitation for a few predefined exceptions, and for example allows raising `Constraint_Error` with a message from a pure subprogram.