[slime-devel] Re: [PATCH] fix for bad source position in ACL6.2/win32

[Matthew Danish]

Helmut Eller <e9626484 at stud3.tuwien.ac.at> writes:
> Matthew Danish <mrd+nospam at cmu.edu> writes:
> 
> > This quick hack counts the number of carriage returns that need to be
> > subtracted from the file-position.  It runs quickly enough on large
> > (15msec to count CRs for 4481 lines in a file I am testing) files that
> > I think it should be acceptable, unless someone has a better idea.  I
> > don't know if 7.0 has this problem as well; if not then this could be
> > conditionalized.
> 
> The problem is the same with 7.0 if I open a file with DOS-style
> eol-conversion.  At least on Linux.  The Allegro manual says something
> about #\newline#\linefeed -> \#newline conversion under Windows, but I
> didn't understand when exactly it is used.  Let's use your patch until
> somebody encounters a real problem.

Well I'm pretty sure that what is happening is that READ-CHAR is doing
the necessary transformation on the input stream to convert
#\return#\linefeed to #\newline, but the source file recording
mechanism is using FILE-POSITION to record the location of the form.
If you run a simple test like this:

(defun test (file) 
  (with-open-file (stream file :direction :input)
    (loop for char = (read-char stream nil nil)
          while char do
            (format t "~S ~S~%" char (file-position stream)))))

Then you will see that the file-position advances twice everytime
#\Newline is encountered.  The entry for FILE-POSITION in the Allegro
documentation seems to indicate this as well.

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