pab@lucid.com (Peter Benson) (06/24/91)
You should use this idiom:
(let ((abort t)
(list-of-file-to-open (find-files-to-open))
(list-of-streams-to-close ()))
(unwind-protect
(progn
(dolist (file list-of-files-to-open)
(push (open-my-file file) list-of-streams-to-close))
(do-stuff-with-streams list-of-streams-to-close)
(setq abort nil))
(dolist (stream list-of-streams-to-close)
(close stream :abort abort))))
If you bomb out in the middle of do-stuff-with-streams then all the files
will be closed properly.
If you macroexpand with-open-file you will find that it uses the same idiom
only with one file and stream.pld@whopper.lcs.mit.edu (Peter L. DeWolf) (06/24/91)
> Is there some way (a macro?) that I can get the functionality of > with-open-file and with-open-stream without initially knowing how many > files (or stream) I will have initially? My current solution is to > open all the files, run the body of the program, and then close > everything. This is fine, until my program bombs (and it's kinda > large) and I have to remember to close out all the streams by hand. The primitive used by (with-open-file) to close things in the face of errors is (unwind-protect). That's easy enough to use. Here's a trivial function that opens an arbitrary number of files and causes an error. It automatically closes the files even if you abort out of the error. (defun open-many-files (&rest files) (let ((streams nil)) (unwind-protect (progn (dolist (file files) (push (open file) streams)) (error "Too bad")) ;;Here's the cleanup form. Close all the files... (dolist (stream streams) (close stream))))) - Peter -- Peter L. DeWolf Motorola Cambridge Research Center pld@mcrc.mot.com -or- pld@abp.lcs.mit.edu
vinson@linc.cis.upenn.edu (Jack Vinson) (06/24/91)
Hello again lisp.hackers, I am reading a bunch of data into lisp from a number of files which isn't that big of a deal, I can simply nest several with-open-file's. The problem occurs when I do not know, a priori, the number of data files from which I will be reading. i.e. That number is read in as well. Is there some way (a macro?) that I can get the functionality of with-open-file and with-open-stream without initially knowing how many files (or stream) I will have initially? My current solution is to open all the files, run the body of the program, and then close everything. This is fine, until my program bombs (and it's kinda large) and I have to remember to close out all the streams by hand. Jack Vinson vinson@linc.cis.upenn.edu
miller@FS1.cam.nist.gov (Bruce R. Miller) (06/25/91)
In article <45084@netnews.upenn.edu>, Jack Vinson writes: > > Hello again lisp.hackers, > > I am reading a bunch of data into lisp from a number of files which isn't that > big of a deal, I can simply nest several with-open-file's. The problem occurs > when I do not know, a priori, the number of data files from which I will be > reading. i.e. That number is read in as well. > > Is there some way (a macro?) that I can get the functionality of with-open-file > and with-open-stream without initially knowing how many files (or stream) I > will have initially? My current solution is to open all the files, run the > body of the program, and then close everything. This is fine, until my program > bombs (and it's kinda large) and I have to remember to close out all the > streams by hand. > > > Jack Vinson vinson@linc.cis.upenn.edu It's not too clear what you're doing with all those files, but I'll try to offer some alternatives. You seem to want them all open while the program is running. Could you alternatively, read them one at a time into some sort of data structure? Otherwise, you could use recursion; recurse until all files are open then within that do whatever you want. But what do you do with the streams, though? collect them into a list? If so, then consider: with-open-file/stream use an unwind-protect to achieve the automatic closing. You also could use unwind-protect; within the `protected-form' you would loop, open each file, collect the streams into a list. then do whatever you want with the streams. The `cleanup-forms' would loop through opened streams and close them. bruce miller@cam.nist.gov