Invalid read syntax for compiled bool vector

Invalid read syntax for compiled bool vector

[Lars Brinkhoff]

I run these forms (in the *scratch* buffer or with M-C-x) to create a
source file and byte-compile it:

  (with-temp-file "test.el"
    (princ `(defun foo ()
             ,(let ((vec (make-bool-vector 20 t)))
                (dolist (i '(11 13 16 18) vec)
                  (aset vec i nil))))
           (current-buffer)))
  (byte-compile-file "test.el")

When I load the compiled file:

  (load-file "test.elc")

I get this error:

  Invalid read syntax: "#&..."

The pattern in the last 12 elements of the bool vector is what
triggers the error.  The contents of the first 8 elements doesn't
seem to affect the result.

This happens in both GNU Emacs 21.3 and 20.7, running in Debian
GNU/Linux on a PowerPC.

-- 
Lars Brinkhoff,         Services for Unix, Linux, GCC, HTTP
Brinkhoff Consulting    http://www.brinkhoff.se/

Re: Invalid read syntax for compiled bool vector

[Lars Brinkhoff]

Richard Stallman <rms@gnu.org> writes:
>       (with-temp-file "test.el"
> 	(princ `(defun foo ()
> 		 ,(let ((vec (make-bool-vector 20 t)))
> 		    (dolist (i '(11 13 16 18) vec)
> 		      (aset vec i nil))))
> 	       (current-buffer)))
> 
> When I run that, it asks me what coding system to use when saving it.
> 
> When I add ;; -*-coding: no-conversion; -*- as the first line,
> there is no problem.

Apparently, you have to bind coding-system-for-write before writing a
source file with a literal bool-vector constant in it, or else Emacs
will either ask the user for the coding system, or write the file
using some default coding system which may not do the right thing.

Also, you have to bind coding-system-for-read before byte-compiling
such a file:

    (let ((coding-system-for-write 'no-conversion))
      (with-temp-file "test.el"
        (prin1 `(defun foo ()
                  ,(let ((vec (make-bool-vector 20 t)))
                     (dolist (i '(11 13 16 18) vec)
                       (aset vec i nil))))
               (current-buffer))))
    (let ((coding-system-for-read 'no-conversion))
      (byte-compile-file "test.el"))
    (load-file "test.elc")
    
In contrast, you don't have to bind coding-system-for-read when byte-
compiling a source file with a string constant:

    (let ((coding-system-for-write 'no-conversion))
      (with-temp-file "test.el"
        (insert (format "(defun foo () \"%s\")" "\377\327\n"))))
    (byte-compile-file "test.el")
    (load-file "test.elc")

Here, the string has the same binary data as the bool vector, but the
compiler handles it more gracefully, in my opinion.

I guess this isn't exactly a bug, but perhaps the Emacs Lisp manual
should say something about binding coding-system-for-read and
coding-system-for-write when reading and writing source files.

-- 
Lars Brinkhoff,         Services for Unix, Linux, GCC, HTTP
Brinkhoff Consulting    http://www.brinkhoff.se/