Using a few simple functions and conventions, it is easy to write ATN-like programs directly in Lisp. Each grammar rule becomes a Lisp function.
(DEFUN < phrase-name> ()
(LET (< local variables> )
(SAVEPTR) ; always the first action
(IF (AND (CAT < category> )
; to test parts of speech
(NEXT) ; move to next word
... )
(PROGN (SUCCESS) ; it worked
< semantics> )
(FAIL)) )) ; parsing failed
Results may be either returned or stored in global registers or
database as a side effect.