Implement ## reader macro

* src/lread.c (read1): Read ## as empty symbol.

* src/print.c (print_object): Print empty symbol as ##.

3 files changed, 18 insertions, 3 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index f6f64f4211d..3eaa3d5eadd 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,9 @@
+2011-07-28  Andreas Schwab  <schwab@linux-m68k.org>
+
+        * print.c (print_object): Print empty symbol as ##.
+
+        * lread.c (read1): Read ## as empty symbol.
+
 2011-07-28  Alp Aker  <alp.tekin.aker@gmail.com>
 
         * nsfns.m (x_set_foreground_color): Set f->foreground_pixel when
diff --git a/src/lread.c b/src/lread.c
index 0613ad037bf..78ff195e990 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -2670,6 +2670,9 @@ read1 (register Lisp_Object readcharfun, int *pch, int first_in_list)
             }
           goto read_symbol;
         }
+      /* ## is the empty symbol.  */
+      if (c == '#')
+        return Fintern (build_string (""), Qnil);
       /* Reader forms that can reuse previously read objects.  */
       if (c >= '0' && c <= '9')
         {
diff --git a/src/print.c b/src/print.c
index f1907a31465..35f89860843 100644
--- a/src/print.c
+++ b/src/print.c
@@ -1536,13 +1536,19 @@ print_object (Lisp_Object obj, register Lisp_Object printcharfun, int escapeflag
         else
           confusing = 0;
 
+        size_byte = SBYTES (name);
+
         if (! NILP (Vprint_gensym) && !SYMBOL_INTERNED_P (obj))
           {
             PRINTCHAR ('#');
             PRINTCHAR (':');
           }
-
-        size_byte = SBYTES (name);
+        else if (size_byte == 0)
+          {
+            PRINTCHAR ('#');
+            PRINTCHAR ('#');
+            break;
+          }
 
         for (i = 0, i_byte = 0; i_byte < size_byte;)
           {
@@ -1555,7 +1561,7 @@ print_object (Lisp_Object obj, register Lisp_Object printcharfun, int escapeflag
               {
                 if (c == '\"' || c == '\\' || c == '\''
                     || c == ';' || c == '#' || c == '(' || c == ')'
-                    || c == ',' || c =='.' || c == '`'
+                    || c == ',' || c == '.' || c == '`'
                     || c == '[' || c == ']' || c == '?' || c <= 040
                     || confusing)
                   PRINTCHAR ('\\'), confusing = 0;