Can UNREAD completely undo READCHAR?

Can UNREAD completely undo READCHAR?

[Leo]

Hello all,

I tried the following experiment (as in the attached patch) and emacs
failed to dump. Any ideas? Thanks in advance.

(gdb) r -batch -l loadup
Starting program: /Users/Shared/emacs/src/temacs -batch -l loadup
Reading symbols for shared libraries .++++++++++++........................................................................................ done
Loading loadup.el (source)...
Using load-path (/Users/Shared/emacs/lisp)
Loading emacs-lisp/byte-run...
Invalid read syntax: "#"

Program exited with code 0377.
(gdb) bt
No stack.
(gdb) 


diff --git a/src/lread.c b/src/lread.c
index 94d47d5..e28e70a 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -1664,7 +1664,7 @@ readevalloop (readcharfun, stream, sourcename, evalfun,
      Lisp_Object unibyte, readfun;
      Lisp_Object start, end;
 {
-  register int c;
+  register int c, c2;
   register Lisp_Object val;
   int count = SPECPDL_INDEX ();
   struct gcpro gcpro1, gcpro2, gcpro3, gcpro4;
@@ -1760,6 +1760,9 @@ readevalloop (readcharfun, stream, sourcename, evalfun,
 	  || c == 0x8a0)  /* NBSP */
 	goto read_next;
 
+      c2 = READCHAR;
+      UNREAD (c2);
+
       if (!NILP (Vpurify_flag) && c == '(')
 	{
 	  record_unwind_protect (unreadpure, Qnil);


Leo

Re: Can UNREAD completely undo READCHAR?

[Andreas Schwab]

Leo <sdl.web@gmail.com> writes:

> I tried the following experiment (as in the attached patch) and emacs
> failed to dump. Any ideas? Thanks in advance.

You can unread at most one character.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Re: Can UNREAD completely undo READCHAR?

[Leo]

On 2010-12-28 22:10 +0000, Andreas Schwab wrote:
> Leo <sdl.web@gmail.com> writes:
>
>> I tried the following experiment (as in the attached patch) and emacs
>> failed to dump. Any ideas? Thanks in advance.
>
> You can unread at most one character.
>
> Andreas.

Thanks.

Does that mean `load' can only test single char i.e. ; or spaces. If I
put #@3abc at the end of any lisp file, load produces an error. Do you
see a simple way of fixing this? (I want this so that a false feature
expression at the end of file won't cause any load error). Thank you.

Cheers,
Leo