* with-input-from-file, call-with-input-file, with-output-to-file,

and call-with-output-file no longer use dynamic-wind to track if
  an exit continuation is invoked multiple times.

TODO

@@ -1,4 +1,5 @@
 * Guardians:
+CHECK  - Implement guardians. 
   - clean up after file ports are dead by flushing/closing the
     underlying file handle.
 

src/libchezio.ss

@@ -679,16 +679,15 @@
          (error 'with-output-to-file "~s is not a procedure" proc))
        (let ([p (apply open-output-file name args)]
              [shot #f])
-         (parameterize ([current-output-port p])
+         (call-with-values 
-           (dynamic-wind 
+           (lambda () 
-             (lambda () 
+             (parameterize ([current-output-port p])
-               (when shot
+               (proc)))
-                 (error 'with-output-to-file 
+           (case-lambda
-                        "cannot reenter")))
+             [(v) (close-output-port p) v]
-             proc
+             [v*
-             (lambda () 
+              (close-output-port p)
-               (close-output-port p)
+              (apply values v*)])))))
-               (set! shot #t)))))))
   
   (primitive-set! 'call-with-output-file
      (lambda (name proc . args)
@@ -696,16 +695,13 @@
          (error 'call-with-output-file "~s is not a string" name))
        (unless (procedure? proc)
          (error 'call-with-output-file "~s is not a procedure" proc))
-       (let ([p (apply open-output-file name args)]
+       (let ([p (apply open-output-file name args)])
-             [shot #f])
+         (call-with-values (lambda () (proc p))
-         (dynamic-wind 
+            (case-lambda
-           (lambda () 
+              [(v) (close-output-port p) v]
-             (when shot
+              [v*
-               (error 'call-with-output-file "cannot reenter")))
+               (close-output-port p)
-           (lambda () (proc p))
+               (apply values v*)])))))
-           (lambda () 
-             (close-output-port p)
-             (set! shot #t))))))
   
   (primitive-set! 'with-input-from-file
      (lambda (name proc)
@@ -713,33 +709,28 @@
          (error 'with-input-from-file "~s is not a string" name))
        (unless (procedure? proc)
          (error 'with-input-from-file "~s is not a procedure" proc))
-       (let ([p (open-input-file name)]
+       (let ([p (open-input-file name)])
-             [shot #f])
+         (call-with-values 
-         (parameterize ([current-input-port p])
+           (lambda () 
-           (dynamic-wind 
+             (parameterize ([current-input-port p])
-             (lambda () 
+               (proc)))
-               (when shot
+           (case-lambda
-                 (error 'with-input-from-file 
+             [(v) (close-input-port p) v]
-                        "cannot reenter")))
+             [v*
-             proc
+              (close-input-port p)
-             (lambda () 
+              (apply values v*)])))))
-               (close-input-port p)
+    
-               (set! shot #t)))))))
-  
   (primitive-set! 'call-with-input-file
      (lambda (name proc)
        (unless (string? name) 
          (error 'call-with-input-file "~s is not a string" name))
        (unless (procedure? proc)
          (error 'call-with-input-file "~s is not a procedure" proc))
-       (let ([p (open-input-file name)]
+       (let ([p (open-input-file name)])
-             [shot #f])
+         (call-with-values (lambda () (proc p))
-         (dynamic-wind 
+            (case-lambda
-           (lambda () 
+              [(v) (close-input-port p) v]
-             (when shot
+              [v*
-               (error 'call-with-input-file "cannot reenter")))
+               (close-input-port p)
-           (lambda () (proc p))
+               (apply values v*)])))))
-           (lambda () 
-             (close-input-port p)
-             (set! shot #t))))))
 )

src/makefile.ss

@@ -83,7 +83,7 @@
     file-exists? delete-file + - add1 sub1 * expt 
     quotient+remainder quotient remainder number? positive?
     negative? zero? number->string logand = < > <= >=
-    make-guardian
+    make-guardian weak-cons
     ))
 
 (define system-primitives