[plt-scheme] The filename of the file in the definition window

From: Matthew Flatt (mflatt at cs.utah.edu)
Date: Thu Dec 20 08:51:54 EST 2007

At Wed, 19 Dec 2007 16:39:32 -0600, "Robby Findler" wrote:
> On Dec 19, 2007 4:15 PM, Matthew Flatt <mflatt at cs.utah.edu> wrote:
> > Avoid creating pipes, because it creates too much work for you in
> > managing a concurrent copy operation and closing the pipe at the right
> > time. Instead, parameterize the call to `system' to set
> > `current-input-port' to your port.

I was reacting in part to this thread:


> I would have thought that something like
>   (thread (lambda () (copy-port  ...) (close-*-port ..)))
> would have been all you'd need.

Plus the `thread-wait's, which you have. You're relatively good at
this. :)

Also, it would be a good idea to wait until the process is done. If the
process explicitly closes its stdout and stderr before existing, and if
you create processes in a loop, it's possible (though unlikely) that
you'd create processes faster than they terminate.

Still, I think it's too much work in the sense that `system' will do
all of that for you, and it will do it more efficiently in some cases
(like this one, where the port is a file port). Just write

 (define (run-wc-on-file filename)
   (call-with-input-file filename
     (λ (file-port)
       (parameterize ([current-input-port file-port])
         (system wc)))))

The first three lines are as in your code, the last two lines replace
another 16.


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