Re: [Axiom-developer] Unions in Spad

[Waldek Hebisch]

Stephen Wilson wrote:
> "Bill Page" <address@hidden> writes:
> 
> > On 08 Jul 2007 15:21:52 -0400, Stephen Wilson wrote:
> > > If so, I have a strategy to make such Unions usable (but it may be a
> > > while before I find the time to implement it). If not, then there is
> > > an easy fix to assert the uniformity of Union branches.
> > >
> > 
> > I think mixed union constructions should be consider syntax errors.
> 
> I personally agree as well.  Unfortunately, the current Spad parser
> is, well, difficult to change.  I can check the uniformity of Union
> branches at a post-parsing stage to at least get the assertion into
> the system.  Perhaps in time my new parser could be used as a full
> replacement for the current one.  
> 

A little nitpick: if mixed union constructions are considered errors
for me it is clearly a semantic error.  I think it is better to catch
such errors on a post-parsing stage.  Why this may matter: syntax
errors frequently leave parser in a confused state, making hard to
detect other errors.   Also for users is seem easier to have simple
syntax + set of semantic constraints than to encode constraints
in syntax.

-- 
                              Waldek Hebisch
address@hidden