; COSC 152
; Fall 2005
; Dennis Brylow
;
; Lecture 25 Demo
; Interactive interpreter fragments.

; read-eval-print loop as in EoPL.  Doesn't take well to EOF.
(define read-eval-print
  (sllgen:make-rep-loop "--> " evaluate
                        (sllgen:make-stream-parser scanner-hw8 grammar-hw8)))

; A little Scheme I/O work to read in text strings with matched parens.
(define (read-string)
  (letrec ([read-helper
            (lambda (lst depth)
              (let ([c (read-char)])
                (cond
                  ((eof-object? c) c)
                  ((eq? c #\newline )
                   (if (zero? depth)
                       (reverse lst)
                       (read-helper lst depth)))
                  ((eq? c #\( )
                   (read-helper (cons c lst) (+ 1 depth)))
                  ((eq? c #\) )
                   (read-helper (cons c lst) (- depth 1)))
                  (else
                   (read-helper (cons c lst) depth))
                  )))]
           [str (read-helper '() 0)])
    (if (eof-object? str)
        str
        (list->string str))))

; A read-eval-print loop using the string parser and our own string input
; routine.
(define interpreter
  (lambda ()
    (begin
      (display "--> ")
      (let ([ in (read-string)])
        (if (eof-object? in)
            'eof
            (begin
              (write (evaluate (parse in)))
              (newline)
              (interpreter))
            )))))