Re: hash-table-{to, from}-alist

[Ted Zlatanov]

On Wed, 26 Nov 2008 15:16:41 -0600 Ted Zlatanov <address@hidden> wrote: 

TZ> The patch below does all the previously discussed formatting plus
TZ> detection of circular references and Davis Herring's suggestion of
TZ> skipping the first preliminary space.  The old-style hashtable printout
TZ> is disabled with an #ifdef, so only the new style is available.

The attached patch does reading and writing of hashtables.  I believe
it works correctly and handles the common error cases.  Please review.

Here are the issues:

- I don't know how to manage a dynamic array of Lisp_Object objects, as
  make-hash-table wants.  What I have right now is hacky and breaks for
  more than 5 parameters (e.g. reading #s(hash-table size 4 size 5 size
  4 size 5 size 4 weakness x) will ignore the weakness parameter.
  Ideally I'd put the arguments in a list and pass that off to
  make-hash-table, but I couldn't find an example of that in the source
  (casting a list of an array of Lisp_Object elements).  Additionally I
  use xmalloc without freeing the memory; I don't know if that will
  cause issues but I saw it used in other places without freeing the
  memory.

- it seems to me that
                      EQ(head, Qhash_table_size_marker) ||
                      EQ(head, Qhash_table_test_marker) ||
                      EQ(head, Qhash_table_weakness_marker) ||
                      EQ(head, Qhash_table_rehash_size_marker) ||
                      EQ(head, Qhash_table_rehash_threshold_marker))
  can be written better, but I don't know enough to do it right.  In
  addition, I don't know how to convert all those parameters to their :
  plist version, e.g. size => :size.  I'm sure it's trivial but couldn't
  find it in the source.  I really wish I could write all this in ELisp :)

- my code is very deliberate, using CAR_SAFE and CDR_SAFE a lot.  If
  that causes performance issues, please suggest improvements.  Ditto
  for anything else--remember this is my first trip to the C side of
  Emacs and treat everything with suspicion.

Thanks
Ted

? hashprint.patch
Index: lread.c
===================================================================
RCS file: /sources/emacs/emacs/src/lread.c,v
retrieving revision 1.401
diff -u -r1.401 lread.c
--- lread.c     7 Sep 2008 20:41:10 -0000       1.401
+++ lread.c     1 Dec 2008 21:48:58 -0000
@@ -80,6 +80,13 @@
 extern int errno;
 #endif
 
+/* hash table read constants */
+Lisp_Object Qhash_table_read_marker, Qhash_table_data_marker;
+Lisp_Object Qhash_table_test_marker, Qhash_table_size_marker;
+Lisp_Object Qhash_table_weakness_marker;
+Lisp_Object Qhash_table_rehash_size_marker;
+Lisp_Object Qhash_table_rehash_threshold_marker;
+
 Lisp_Object Qread_char, Qget_file_char, Qstandard_input, Qcurrent_load_list;
 Lisp_Object Qvariable_documentation, Vvalues, Vstandard_input, 
Vafter_load_alist;
 Lisp_Object Qascii_character, Qload, Qload_file_name;
@@ -2341,6 +2348,89 @@
 
     case '#':
       c = READCHAR;
+      if (c == 's')
+       {
+         c = READCHAR;
+         if (c == '(')
+           {
+             /*
+               Accept extended format for hashtables (extensible to
+               other types), e.g.
+               #s(hash-table size 2 test equal data (k1 v1 k2 v2))          
+             */
+             Lisp_Object tmp = read_list (0, readcharfun);
+             Lisp_Object head = CAR_SAFE(tmp);
+             Lisp_Object data = Qnil;
+             Lisp_Object val = Qnil;
+             /* will this be freed automatically? */         
+             Lisp_Object* params = (Lisp_Object*) xmalloc (10 * 
sizeof(Lisp_Object));
+             int param_count = 0;
+             if (!EQ (head, Qhash_table_read_marker))
+               error ("Invalid extended read marker at head of #s list"
+                      "(only hash-table allowed)");
+
+             while (!NILP(tmp))
+               {
+                 tmp = CDR_SAFE(tmp);
+                 head = CAR_SAFE(tmp);
+                 /* allowed parameters: size test weakness
+                    rehash-size rehash-threshold */
+                 if (EQ(head, Qhash_table_data_marker))
+                   {
+                     tmp = CDR_SAFE(tmp);
+                     data = CAR_SAFE(tmp);
+                     /* debug_print(data); */
+                   }
+
+                 if (
+                     param_count < 9 &&
+                     EQ(head, Qhash_table_size_marker) ||
+                     EQ(head, Qhash_table_test_marker) ||
+                     EQ(head, Qhash_table_weakness_marker) ||
+                     EQ(head, Qhash_table_rehash_size_marker) ||
+                     EQ(head, Qhash_table_rehash_threshold_marker))
+                   {
+                     tmp = CDR_SAFE(tmp);
+                     val = CAR_SAFE(tmp);
+                     /*
+                       debug_print(head);
+                       debug_print(val);
+                     */
+                     /* how do I turn head into a symbol with the same 
contents but beginning with ':'? */
+                     params[param_count] = head;
+                     params[param_count+1] = val;
+                     param_count+=2;
+                   }
+               }
+
+             if (NILP(data))
+               error ("No data marker was found in the hash table");
+
+             /* doesn't work because of 'size' vs. ':size' issue, see above
+                Lisp_Object ht = Fmake_hash_table(param_count, params);
+             */
+             Lisp_Object ht = Fmake_hash_table(0, NULL);
+
+             Lisp_Object key = Qnil;
+             
+             while (!NILP(data))
+               {
+                 key = CAR_SAFE(data);
+                 data = CDR_SAFE(data);
+                 val = CAR_SAFE(data);
+                 data = CDR_SAFE(data);
+                 if (NILP(val))
+                   error ("Odd number of elements in hashtable data");
+                 /*
+                   debug_print(key);
+                   debug_print(val);
+                 */
+                 Fputhash(key, val, ht);
+               }
+             
+             return ht;
+           }   
+       }
       if (c == '^')
        {
          c = READCHAR;
@@ -4432,6 +4522,21 @@
 
   Vloads_in_progress = Qnil;
   staticpro (&Vloads_in_progress);
+
+  Qhash_table_read_marker = intern ("hash-table");
+  staticpro (&Qhash_table_read_marker);
+  Qhash_table_data_marker = intern ("data");
+  staticpro (&Qhash_table_data_marker);
+  Qhash_table_test_marker = intern ("test");
+  staticpro (&Qhash_table_size_marker);
+  Qhash_table_test_marker = intern ("size");
+  staticpro (&Qhash_table_size_marker);
+  Qhash_table_weakness_marker = intern ("weakness");
+  staticpro (&Qhash_table_weakness_marker);
+  Qhash_table_rehash_size_marker = intern ("rehash-size");
+  staticpro (&Qhash_table_rehash_size_marker);
+  Qhash_table_rehash_threshold_marker = intern ("rehash-threshold");
+  staticpro (&Qhash_table_rehash_threshold_marker);
 }
 
 /* arch-tag: a0d02733-0f96-4844-a659-9fd53c4f414d
Index: print.c
===================================================================
RCS file: /sources/emacs/emacs/src/print.c,v
retrieving revision 1.253
diff -u -r1.253 print.c
--- print.c     31 Jul 2008 05:33:53 -0000      1.253
+++ print.c     1 Dec 2008 21:48:58 -0000
@@ -1341,6 +1341,7 @@
  loop:
   if (STRINGP (obj) || CONSP (obj) || VECTORP (obj)
       || COMPILEDP (obj) || CHAR_TABLE_P (obj) || SUB_CHAR_TABLE_P (obj)
+      || HASH_TABLE_P (obj)
       || (! NILP (Vprint_gensym)
          && SYMBOLP (obj)
          && !SYMBOL_INTERNED_P (obj)))
@@ -1536,6 +1537,7 @@
   /* Detect circularities and truncate them.  */
   if (STRINGP (obj) || CONSP (obj) || VECTORP (obj)
       || COMPILEDP (obj) || CHAR_TABLE_P (obj) || SUB_CHAR_TABLE_P (obj)
+      || HASH_TABLE_P (obj)
       || (! NILP (Vprint_gensym)
          && SYMBOLP (obj)
          && !SYMBOL_INTERNED_P (obj)))
@@ -2036,6 +2038,7 @@
       else if (HASH_TABLE_P (obj))
        {
          struct Lisp_Hash_Table *h = XHASH_TABLE (obj);
+#if 0
          strout ("#<hash-table", -1, -1, printcharfun, 0);
          if (SYMBOLP (h->test))
            {
@@ -2052,6 +2055,61 @@
          sprintf (buf, " 0x%lx", (unsigned long) h);
          strout (buf, -1, -1, printcharfun, 0);
          PRINTCHAR ('>');
+#endif
+         /*
+           implement a readable output, e.g.:
+           #s(hash-table size 2 test equal data (k1 v1 k2 v2))
+         */
+         /* always print the size */
+         sprintf (buf, "#s(hash-table size %ld", (long) XVECTOR 
(h->next)->size);
+         strout (buf, -1, -1, printcharfun, 0);
+
+         if (!NILP(h->test))
+           {
+             strout (" test ", -1, -1, printcharfun, 0);
+             print_object (h->test, printcharfun, 0);
+           }
+
+         if (!NILP(h->weak))
+           {
+             strout (" weakness ", -1, -1, printcharfun, 0);
+             print_object (h->weak, printcharfun, 0);
+           }
+
+         if (!NILP(h->rehash_size))
+           {
+             strout (" rehash-size ", -1, -1, printcharfun, 0);
+             print_object (h->rehash_size, printcharfun, 0);
+           }
+
+         if (!NILP(h->rehash_threshold))
+           {
+             strout (" rehash-threshold ", -1, -1, printcharfun, 0);
+             print_object (h->rehash_threshold, printcharfun, 0);
+           }
+
+         strout (" data ", -1, -1, printcharfun, 0);
+
+         /* print the data here as a plist */
+         int i;
+         int printed=0;
+
+         PRINTCHAR ('(');
+         for (i = 0; i < HASH_TABLE_SIZE (h); ++i)
+           if (!NILP (HASH_HASH (h, i)))
+             {
+               if (printed)
+                 {
+                   PRINTCHAR (' ');
+                 }
+               print_object (HASH_KEY (h, i), printcharfun, 0);
+               PRINTCHAR (' ');
+               print_object (HASH_VALUE (h, i), printcharfun, 0);
+               printed = 1;
+             }
+         PRINTCHAR (')');
+         PRINTCHAR (')');
+
        }
       else if (BUFFERP (obj))
        {