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;;  Sample grammar.
;;  Borrowed/adapted from G. Gazdar and C. Mellish, 
;;  Natural Language Processing in Lisp
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(defparameter *start-symbol* 's)

(defparameter *nonterminals* '(s vp np pp det n tv p))

(defparameter *rules*
   (list   
;; Grammar rules
    (make-rule :mother 's :child1 'np :child2 'vp :prob  1)
    (make-rule :mother 'vp :child1 'tv :child2 'np :prob  0.5) 
    (make-rule :mother 'vp :child1 'vp :child2 'vp :prob  0.1 )   
    (make-rule :mother 'vp :child1 'vp :child2 'pp :prob  0.3 )
    (make-rule :mother 'np :child1 'det :child2 'n :prob  0.4 )
    (make-rule :mother 'np :child1 'np :child2 'pp :prob   0.2)
    (make-rule :mother 'pp :child1 'p :child2 'np :prob 1)))

(defparameter *lexicon*
  (list
   ;; Lexicon 
   (make-lexeme :pos 'vp :form 'run :prob 0.1)
   (make-lexeme :pos 'det :form 'her :prob 1)
   (make-lexeme :pos 'np :form 'her :prob  0.2)
   (make-lexeme :pos 'np :form 'they :prob 0.2 )
   (make-lexeme :pos 'n :form 'nurses :prob 0.25 )
   (make-lexeme :pos 'tv :form 'nurses :prob  0.2)
   (make-lexeme :pos 'n :form 'book :prob  0.25)
   (make-lexeme :pos 'tv :form 'book :prob  0.2)
   (make-lexeme :pos 'n :form 'travel :prob  0.25)
   (make-lexeme :pos 'tv :form 'travel :prob  0.2)
   (make-lexeme :pos 'n :form 'report :prob  0.25)
   (make-lexeme :pos 'tv :form 'report :prob  0.2)
   (make-lexeme :pos 'tv :form 'hear :prob  0.2)
   (make-lexeme :pos 'tv :form 'see :prob  0.2)
   (make-lexeme :pos 'p :form 'on :prob  1)))