[developers] Defaults in TDL

goodman.m.w at gmail.com goodman.m.w at gmail.com
Tue Sep 4 19:42:13 CEST 2018

Hello everyone,

I appreciate the feedback I've received in previous messages in my attempts
to dust off neglected corners of TDL syntax, and I'd now like to bring up
"defaults", or "defeasible constraints" (I believe these refer to the same
thing). Are we prepared to start supporting defaults/defeasible-constraints
in our processors and using them in our grammars? Or should we discard them
as an undesired experimental feature (i.e., declare them to *not* be part

Further information:

Currently, only the LKB supports them (and maybe PET?). As I understand,
they are a compile-time feature, meaning that they change how the grammar
is compiled and that there is no longer a notion of "defaults" during
run-time. I don't think the use of defaults causes any change in the
competence or performance of a grammar.

The benefit of defaults is for the grammar engineer as it can reduce the
amount of boilerplate code and make the grammar source code more intuitive.
I think any result that makes grammar writing easier is a big win. The
differences it creates between the source-code form of the grammar and the
compiled hierarchy, however, can complicate debugging (e.g., interactive

Some links:
  - http://www.aclweb.org/anthology/J99-1002
  - http://moin.delph-in.net/ParisDefeasibleConstraints
  - http://moin.delph-in.net/StanfordDefaults

-Michael Wayne Goodman
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