(module mp2-soln (lib "eopl.ss" "eopl")

  (require "drscheme-init.scm")
  (provide scan&parse value-of-aexp-string)

  (define the-lexer
    ;; need to write this
    )

  (define the-grammar
    ;; need to write this
    )

  (sllgen:make-define-datatypes the-lexer the-grammar)

  (define show-the-datatypes
    (lambda () (sllgen:show-define-datatypes the-lexer the-grammar)))

  (define scan&parse
    (sllgen:make-string-parser the-lexer the-grammar))

  (define just-scan
    (sllgen:make-string-scanner the-lexer the-grammar))

  (define value-of-aexp-string
    (lambda (str)
      (value-of-aexp (scan&parse str))))

  ;; need to write value-of-aexp and its associated help functions here.
  
 
  )