Re: Running a preprocessor from GPS?

["G.B." <bauhaus@futureapps.invalid>]

On 30.07.15 10:45, EGarrulo wrote:

>> I'm still
>> not sure anything but messages should go with exceptions: it is
>> too tempting for consultants to apply techniques of obfuscation
>> via exception classes. Even involuntarily!
>
> Could you explain further, please?

Dmitry has explained the context for a handler.

As you explained "chaining", exceptions can propagate
and be exchanged for different exceptions, perhaps after
intermediate handling.

But all the "programming" and "executing" going on when
exceptions are regular objects, or when exception messages
are concatenated, is dubious IMHO. Hack-ish. Instead, in
languages without pre-allocated environments such as Ada
or C++, I'd rather do bookkeeping of all information that
is needed for restarting, if possible, at any level of
handling.

Conceptually, maybe not always applicable:

   declare
      P : Protocol;  -- representing known good state
   begin
      --  either pass P to Op, or maybe have
      --  Op use P as a relatively global variable
      Op (...);
   exception
      when Not_Program_Error_Etc =>
         --  we now have a P ready for inspection
         ...
   end;

In fact, sometimes this is the only way one can handle
exceptions across task borders; Google's App Engine is
one example. One process never knows what is going on in some
separate process unless the other process leaves information
in the datastore, at some location known to both processes.


Involuntary obfuscation happens when the programmer codes
any knowledge of various parts of a program into exception types:
If a programmer knows two different parts of the program,
defines the exception's type in one and uses the thrown
object in the other, there is no trace of this knowledge in
the program's source text. IOW, knowing the conditions
of non-local flow entirely depends on good will, discipline,
conventions, documentation, etc., but not on language.

That's unlike P above: both parts, the one that finally
raises, as well as the handling part will refer to it.
It doesn't look elegant, but it works in general.