;;; Hey, emacs, this file is -*- Mode: tdl; -*- ... got that?

;;;
;;; the type hierachy, introducing sub-types and appropriate features
;;;


feat-struc := *top*.

expression := feat-struc & 
[ HEAD pos,
  VAL valence ].

valence := feat-struc &
[ SPR *list*,
  COMPS *list* ].

pos := feat-struc.

noun := pos.

verb := pos.

det := pos.


phrase := expression &
[ ARGS *list* ].

word := expression &
[ ORTH *string* ].

root := phrase &
[ HEAD verb,
  VAL [ SPR < >,
        COMPS < > ] ].

;;;
;;; a few `non-linguistic' types: the top type for all strings (i.e. type names
;;; enclosed in double quotes; no need to declare strings individually) and the
;;; hierarchy of list types (using a FIRST -- REST encoding for list elements
;;; and list tails, respectively).
;;;

*string* := *top*.

*list* := *top*.

*ne-list* := *list* &
 [ FIRST *top*,
   REST *list* ].

*null* := *list*.