[developers] type addenda and :< in TDL

[Ann Copestake]

So shall we agree that if there are no objections by Dec 5th, :< can
become identical in behaviour in type definitions to := ?  I suggest
that if we do add a warning message, that we output only one message
on a grammar load.

Ann


> hi again,
> 
> > from my perspective, it's there for backward compatability, but I'm
> > not keen to get rid of it since it'll cause hassle for no good reason.
> 
> i just had a quick look at the relevant code in the LKB and PET.  if we
> agree the `:=' vs `:<' distinction has no formal status in the DELPH-IN
> formalism, we can just treat `:<' as a syntactic variant.  this will be
> trivial to implement and not show any effect on existing grammars.  we
> could optionally issue a deprecation warning when `:<' is used, or just
> internally suggest to DELPH-IN grammarians that they avoid `:<'.
> 
> > Presumably you will be changing some :< cases to :=, but I don't want
> > to force everyone to change all of them.  You might be able to produce
> > a patch to tdltypeinput.lsp so it doesn't complain if you try and
> > augment a :< type, but that shouldn't be checked in, I feel.
> 
> in fact, the current LKB allows type addenda on types defined by `:<',
> so there is a mild inconsistency here.  PET enforces what i believe was
> the original TDL intention of `:<', viz. a sub-type definition without
> a local constraint (it can still inherit features and constraints).  i
> would like the two systems to behave alike, but to decide what is right
> we would have to ascribe a formal interpretation to `:<', which i think
> we all agree is undesirable.
> 
> i would be happy making the change reading `:<' as `:=' in both worlds.
> i would prefer seing `:<' deprecated.  in my teaching experience, it is
> a potential source of confusion.  would anyone object to that move?
> 
>                                                         cheers  -  oe
> 
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