libguile/pairs.c

   1 /* Copyright (C) 1995,1996,2000,2001, 2004, 2005, 2006, 2008, 2009 Free Software Foundation, Inc.
   2  *
   3  * This library is free software; you can redistribute it and/or
   4  * modify it under the terms of the GNU Lesser General Public License
   5  * as published by the Free Software Foundation; either version 3 of
   6  * the License, or (at your option) any later version.
   7  *
   8  * This library is distributed in the hope that it will be useful, but
   9  * WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  11  * Lesser General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU Lesser General Public
  14  * License along with this library; if not, write to the Free Software
  15  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  16  * 02110-1301 USA
  17  */
  18
  19
  20 \f
  21 #ifdef HAVE_CONFIG_H
  22 # include <config.h>
  23 #endif
  24
  25 #include "libguile/_scm.h"
  26 #include "libguile/validate.h"
  27
  28 #include "libguile/pairs.h"
  29
  30 #include "verify.h"
  31
  32 \f
  33
  34 /* {Pairs}
  35  */
  36
  37 /*
  38  * This compile-time test verifies the properties needed for the
  39  * efficient test macro scm_is_null_or_nil defined in pairs.h,
  40  * which is defined in terms of the SCM_MATCHES_BITS_IN_COMMON macro.
  41  *
  42  * See the comments preceeding the definitions of SCM_BOOL_F and
  43  * SCM_MATCHES_BITS_IN_COMMON in tags.h for more information.
  44  */
  45 verify (SCM_VALUES_DIFFER_IN_EXACTLY_ONE_BIT_POSITION           \
  46                  (SCM_ELISP_NIL, SCM_EOL));
  47
  48
  49 #if (SCM_DEBUG_PAIR_ACCESSES == 1)
  50
  51 #include "libguile/ports.h"
  52 #include "libguile/strings.h"
  53
  54 void scm_error_pair_access (SCM non_pair)
  55 {
  56   static unsigned int running = 0;
  57   SCM message = scm_from_locale_string ("Non-pair accessed with SCM_C[AD]R: `~S'\n");
  58
  59   if (!running)
  60     {
  61       running = 1;
  62       scm_simple_format (scm_current_error_port (),
  63                          message, scm_list_1 (non_pair));
  64       abort ();
  65     }
  66 }
  67
  68 #endif
  69
  70 SCM_DEFINE (scm_cons, "cons", 2, 0, 0,
  71             (SCM x, SCM y),
  72             "Return a newly allocated pair whose car is @var{x} and whose\n"
  73             "cdr is @var{y}.  The pair is guaranteed to be different (in the\n"
  74             "sense of @code{eq?}) from every previously existing object.")
  75 #define FUNC_NAME s_scm_cons
  76 {
  77   return scm_cell (SCM_UNPACK (x), SCM_UNPACK (y));
  78 }
  79 #undef FUNC_NAME
  80
  81
  82 SCM
  83 scm_cons2 (SCM w, SCM x, SCM y)
  84 {
  85   return scm_cons (w, scm_cons (x, y));
  86 }
  87
  88
  89 SCM_DEFINE (scm_pair_p, "pair?", 1, 0, 0,
  90             (SCM x),
  91             "Return @code{#t} if @var{x} is a pair; otherwise return\n"
  92             "@code{#f}.")
  93 #define FUNC_NAME s_scm_pair_p
  94 {
  95   return scm_from_bool (scm_is_pair (x));
  96 }
  97 #undef FUNC_NAME
  98
  99 SCM
 100 scm_car (SCM pair)
 101 {
 102   if (!scm_is_pair (pair))
 103     scm_wrong_type_arg_msg (NULL, 0, pair, "pair");
 104   return SCM_CAR (pair);
 105 }
 106
 107 SCM
 108 scm_cdr (SCM pair)
 109 {
 110   if (!scm_is_pair (pair))
 111     scm_wrong_type_arg_msg (NULL, 0, pair, "pair");
 112   return SCM_CDR (pair);
 113 }
 114
 115 SCM
 116 scm_i_chase_pairs (SCM tree, scm_t_uint32 pattern)
 117 {
 118   do
 119     {
 120       if (!scm_is_pair (tree))
 121         scm_wrong_type_arg_msg (NULL, 0, tree, "pair");
 122       tree = (pattern & 1) ? SCM_CAR (tree) : SCM_CDR (tree);
 123       pattern >>= 2;
 124     }
 125   while (pattern);
 126   return tree;
 127 }
 128
 129 SCM_DEFINE (scm_set_car_x, "set-car!", 2, 0, 0,
 130             (SCM pair, SCM value),
 131             "Stores @var{value} in the car field of @var{pair}.  The value returned\n"
 132             "by @code{set-car!} is unspecified.")
 133 #define FUNC_NAME s_scm_set_car_x
 134 {
 135   SCM_VALIDATE_CONS (1, pair);
 136   SCM_SETCAR (pair, value);
 137   return SCM_UNSPECIFIED;
 138 }
 139 #undef FUNC_NAME
 140
 141
 142 SCM_DEFINE (scm_set_cdr_x, "set-cdr!", 2, 0, 0,
 143             (SCM pair, SCM value),
 144             "Stores @var{value} in the cdr field of @var{pair}.  The value returned\n"
 145             "by @code{set-cdr!} is unspecified.")
 146 #define FUNC_NAME s_scm_set_cdr_x
 147 {
 148   SCM_VALIDATE_CONS (1, pair);
 149   SCM_SETCDR (pair, value);
 150   return SCM_UNSPECIFIED;
 151 }
 152 #undef FUNC_NAME
 153
 154 \f
 155
 156 /* Every cxr-pattern is made up of pairs of bits, starting with the two least
 157  * significant bits.  If in a pair of bits the least significant of the two
 158  * bits is 0, this means CDR, otherwise CAR.  The most significant bits of the
 159  * two bits is only needed to indicate when cxr-ing is ready.  This is the
 160  * case, when all remaining pairs of bits equal 00.  */
 161
 162 typedef struct {
 163   const char *name;
 164   unsigned char pattern;
 165 } t_cxr;
 166
 167 static const t_cxr cxrs[] =
 168 {
 169   {"cdr",    0x02}, /* 00000010 */
 170   {"car",    0x03}, /* 00000011 */
 171   {"cddr",   0x0a}, /* 00001010 */
 172   {"cdar",   0x0b}, /* 00001011 */
 173   {"cadr",   0x0e}, /* 00001110 */
 174   {"caar",   0x0f}, /* 00001111 */
 175   {"cdddr",  0x2a}, /* 00101010 */
 176   {"cddar",  0x2b}, /* 00101011 */
 177   {"cdadr",  0x2e}, /* 00101110 */
 178   {"cdaar",  0x2f}, /* 00101111 */
 179   {"caddr",  0x3a}, /* 00111010 */
 180   {"cadar",  0x3b}, /* 00111011 */
 181   {"caadr",  0x3e}, /* 00111110 */
 182   {"caaar",  0x3f}, /* 00111111 */
 183   {"cddddr", 0xaa}, /* 10101010 */
 184   {"cdddar", 0xab}, /* 10101011 */
 185   {"cddadr", 0xae}, /* 10101110 */
 186   {"cddaar", 0xaf}, /* 10101111 */
 187   {"cdaddr", 0xba}, /* 10111010 */
 188   {"cdadar", 0xbb}, /* 10111011 */
 189   {"cdaadr", 0xbe}, /* 10111110 */
 190   {"cdaaar", 0xbf}, /* 10111111 */
 191   {"cadddr", 0xea}, /* 11101010 */
 192   {"caddar", 0xeb}, /* 11101011 */
 193   {"cadadr", 0xee}, /* 11101110 */
 194   {"cadaar", 0xef}, /* 11101111 */
 195   {"caaddr", 0xfa}, /* 11111010 */
 196   {"caadar", 0xfb}, /* 11111011 */
 197   {"caaadr", 0xfe}, /* 11111110 */
 198   {"caaaar", 0xff}, /* 11111111 */
 199   {0, 0}
 200 };
 201
 202 \f
 203
 204 void
 205 scm_init_pairs ()
 206 {
 207   unsigned int subnr = 0;
 208
 209   for (subnr = 0; cxrs[subnr].name; subnr++)
 210     {
 211       SCM (*pattern) () = (SCM (*) ()) (scm_t_bits) cxrs[subnr].pattern;
 212       scm_c_define_subr (cxrs[subnr].name, scm_tc7_cxr, pattern);
 213     }
 214
 215 #include "libguile/pairs.x"
 216 }
 217
 218
 219 /*
 220   Local Variables:
 221   c-file-style: "gnu"
 222   End:
 223 */