Re: Novice Questions on Ada Exceptions

[stt@inmet]

One frequent cause of PROGRAM_ERROR is an elaboration-order
problem.  Whenever a subprogram is called before it has
been elaborated, PROGRAM_ERROR is raised.  This happens
most frequently when elaboration-time code
in one package calls subprograms in another package,
and the other package's body has not yet been elaborated.
This is something which sometimes shows up in
rehosting since elaboration-order determination is 
implementation-dependent.  

The usual fix is to
determine which package calls which other package at
elaboration time, and place a pragma Elaborate (see LRM 10.5:3)
in the calling package referencing the called package.
Note that if the called package calls other packages, there
may be a need to include additional pragma Elaborates on
those lower level packages.  Pragma Elaborate only forces
elaboration for a single level of dependency.  Hopefully,
Ada 9X will fix it so that it forces elaboration for
the closure of dependencies...

S. Tucker Taft
Intermetrics, Inc.
Cambridge, MA  02138