Thanks for the fix and suggestions. On Fri, Jan 21, 2011 at 1:37 PM, Matthew Flatt <mfl...@cs.utah.edu> wrote:
> At Fri, 21 Jan 2011 10:53:42 -0700, Doug Williams wrote: > > What is the best way to perform actions after a sequence terminates? Here > is > > a simple example that is like in-lines, but takes a path instead of a > port. > > It works, but I was wondering if there is a better way to do it. > > > > (define (in-file-lines path) > > (let ((port (open-input-file path #:mode 'text))) > > (make-do-sequence > > (lambda () > > (values > > (lambda (_) (read-line port 'any)) > > void > > (void) > > void > > (lambda _ (if (eof-object? (peek-byte port)) > > (begin > > (close-input-port port) > > #f) > > #t)) > > void))))) > > I think you mean > > (define (in-file-lines path) > (let ((port (open-input-file path #:mode 'text))) > (make-do-sequence > (lambda () > (values > (lambda (_) (read-line port 'any)) > void > (void) > void > (lambda (v) (if (eof-object? v) ; <---------- > (begin > (close-input-port port) > #f) > #t)) > void))))) > > so that the last line is included in the sequence. Otherwise, I don't > have any better suggestions. > > Beware that if the sequence stops being used before you get to the end > of the file, then the port won't be closed: > > (for ([line (in-file-lines <file>)] > [elem (in-list '(1 2 3))]) > ...) > ; port isn't closed if it has more than 3 lines > > But the sequence protocol doesn't give a sequence any way to know that > it isn't being used, other than GC-based finalization --- which is > probably a bad idea for file ports, since you can run out of available > file descriptors much faster than available memory. > >
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