Bug report ID:635627 - subst([...] is order-dependent

Am Donnerstag, den 01.04.2010, 15:06 -0500 schrieb Barton Willis:
> > I think it's bad to change subst to do parallel because that changes
> > existing behavior.  There could be lots of code out there that depends
> > on this and we should gratuitiously break them. 
> 
> I agree. My enthusiasm for breaking existing code is low. But the user
> documentation for subst doesn't specify the substitution order (or
> simplification order), so there is an argument for saying that code
> that depends on a specific substitution order is buggy.

When I summarize the different opinions I think it is the best not to
change the current implementation of subst, to add some documentation
about the way substitute works, and to close the open bug report as
"won't fix".

Perhaps, we have the following additional options:

1. 
Adding a function like psubstitute for parallel substitution which has a
functionality comparable to the function substitute.

2. 
Adding a flag to the existing function substitute to switch on parallel
substitution.

Remark: I think it is not a good idea to try to extend sublis to get a
functionality like substitute, because we have to double a lot of code.

Dieter Kaiser