dyln

#lang plai-typed

;;data def
(define-type FBAPE-expressions
  [numC (n : number)]
  [plusC (l : FBAPE-expressions) (r : FBAPE-expressions)]
  [subC (l : FBAPE-expressions) (r : FBAPE-expressions)]
  [multC (l : FBAPE-expressions) (r : FBAPE-expressions)]
  [expC (l : FBAPE-expressions) (r : FBAPE-expressions)]
 ; [grtrZeroC (a : FBAPE-expressions) (b : FBAPE-expressions) (c : FBAPE-expressions)]

dyln

(define (parse [s : s-expression]) : FBAPEsug
  (cond [(s-exp-number? s) (numS (s-exp->number s))]
    [(s-exp-list? s)
     (let ([sl (s-exp->list s)])
      (cond [(= length sl 3)  
       (case (s-exp->symbol (first sl)) 
         [(+) (plusS (parse (second sl)) (parse (third sl)))]
         [(*) (multS (parse (second sl)) (parse (third sl)))]
         [(-) (bminusS (parse (second sl)) (parse (third sl)))]
         [(**) (expS (parse (second sl)) (parse (third sl)))]