Re: [Jscheme-devel] Re: JScheme SchemeApplet - UC WISE Citris Project

[Timothy H. <tim...@ma...>]

On Sunday, May 26, 2002, at 02:15 PM, Dazhi Liu wrote:
> BTW, a quick question: After user program in JScheme for a while, is
> there an easy way to erase all user defined bindings, that is, to return
> to the initial state of JScheme?
>



Its not too hard. At the end of this note is a procedure that creates a 
SymbolTable
restorer. You use it as

 > (define z (make-state-restorer))
....
 > (z)
and it will restore your state to the initial one.



;; This is a System restorer
;;  It makes a copy of the Symbol table state which it stores in its 
returned value
;;     > (define z (make-state-restorer))
;; When you later invoke the thunk
;;     > (z)
;;  it resets the Symbol table to its
;; original values (but it doesn't reset the javadot primitives as this 
would just
;; waste time).

(define (make-state-restorer)
   (let
       ((ST0
         (java.util.Hashtable.))
        (isJavadot (lambda (x)
            (or (> (.indexOf x ".") -1) (> (.indexOf x "$") -1))))
        (enum->list
         (lambda(E)
           (let loop ((L ()))
             (if (.hasMoreElements E)
                 (loop (cons (.nextElement E) L))
                 L)))))
     (for-each
      (lambda(x)
        (if (not (isJavadot x))  ;; don't remember javadots!
          (.put ST0 x
               (tryCatch
                (list (.getGlobalValue (string->symbol x)))
                (lambda(e)
                  ())))))
      (enum->list (.keys jsint.Symbol.symbolTable$)))

     (display (length (enum->list (.keys ST0))))(newline)

     (lambda()
       (let ((ST jsint.Symbol.symbolTable$))
         (for-each
          (lambda(x)
            (let ((v (.get ST0 x)))
              (if (equal? #null v)
                (if (not (isJavadot x))
                    (begin (display x)(newline) (.remove ST x)))
                (let ((s (string->symbol x)))
                   (.put ST x s)
                   (if (not (null? v))
                    (.setGlobalValue s (first v)))))))
          (enum->list (.keys ST)))))))