;;; lang3-4

(module lang
  (lib "eopl.ss" "eopl")                
  
  (require "drscheme-init.scm")
  
  (provide (all-defined))

  ;;;;;;;;;;;;;;;; grammatical specification ;;;;;;;;;;;;;;;;
  
  (define the-lexical-spec
    '((whitespace (whitespace) skip)
      (comment ("%" (arbno (not #\newline))) skip)
      (identifier
       (letter (arbno (or letter digit "_" "-" "?")))
       symbol)
      (number (digit (arbno digit)) number)
      (number ("-" digit (arbno digit)) number)
      ))
  
  (define the-grammar
    '((program (expression) a-program)

      (expression (number) lit-exp)
      (expression
        ("-" "(" expression "," expression ")")
        diff-exp)
      
      (expression
       ("zero?" "(" expression ")")
       zero?-exp)

      (expression
       ("if" expression "then" expression "else" expression)
       if-exp)

      (expression (identifier) var-exp)

      (expression
       ("let" identifier "=" expression "in" expression)
       let-exp)   

      (expression
       ("proc" "(" identifier ")" expression)
       proc-exp)

      (expression
       ("(" expression expression ")")
       app-exp)

      (expression
        ("letrec"
          identifier "(" identifier ")" "=" expression
           "in" expression)
        letrec-exp)
      
      ))

  (define the-field-names
    '((a-program exp)
      (lit-exp n)
      (zero?-exp e1)
      (if-exp e0 e1 e2)
      (diff-exp e1 e2)
      (var-exp id)
      (let-exp bvar rhs body)
      (proc-exp bvar body)
      (app-exp rator rand)
      (letrec-exp proc-name bvar proc-body letrec-body)
      ))
  
  ;;;;;;;;;;;;;;;; sllgen boilerplate ;;;;;;;;;;;;;;;;
  
  (sllgen:make-define-datatypes the-lexical-spec the-grammar)
  
  (define show-the-datatypes
    (lambda () (sllgen:list-define-datatypes the-lexical-spec the-grammar)))
  
  (define scan&parse
    (sllgen:make-string-parser the-lexical-spec the-grammar))
  
  (define just-scan
    (sllgen:make-string-scanner the-lexical-spec the-grammar))
  
  )