[PD] Why can't you find the source of last error?

[Mathieu Bouchard]

Johannes Zmölnig wrote:
> Matteo.sistisette wrote:
>> Often, when I get an error, such as for example "inlet: no method for
>> 'list'", and I do a "Find last error", I get the message:
>> ...sorry, I couldn't find the source of last error
> then there is a 2nd type of error message, which links a message to a 
> certain object. when an object uses this special kind of error message, 
> you will be able to track the error with the "find last error" menu.
> a C-programmer can often choose to use one of these variants;
> using the 2nd method is a tiny bit more complicated (and requires more
> typing); this is most likely the reason why people do not explicitely
> use it.

A while ago, I started replacing all error() calls by pd_error() calls so 
that error messages can be located better. However, I am considering 
removing pd_error() completely instead, using a system of 
dynamic variables (in LISP parlance).

A dynamic variable is like a global variable that is being used as local 
by backing up and restoring the contents of the variable whenever 
appropriate. Most of the time this is equivalent to lexical variables 
(the other kind of local variables) but in this case this also allows one 
to use the contents of the variable as set by the caller, or the caller 
of the caller, or whoever set the variable last (in terms of levels of 
nesting). This makes pd_error() useless, as any error() call can look up 
the variable that indicates the currently deepest method activation (last 
message received that isn't yet finished handling). This allows 
accurate error-reporting from functions that don't have a "this" parameter 
and have no idea what it could be.

I introduced this feature in GridFlow a long time ago. (currently it's not 
in GridFlow anymore, for reasons that are long to explain, but I still 
think that it's a good idea)

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| Mathieu Bouchard - tél:+1.514.383.3801, Montréal QC Canada