libguile/pairs.c

   1 /* Copyright (C) 1995,1996,2000,2001, 2004, 2005 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
   5  * License as published by the Free Software Foundation; either
   6  * version 2.1 of the License, or (at your option) any later version.
   7  *
   8  * This library is distributed in the hope that it will be useful,
   9  * but 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 02110-1301 USA
  16  */
  17
  18
  19 \f
  20
  21 #include "libguile/_scm.h"
  22 #include "libguile/validate.h"
  23
  24 #include "libguile/pairs.h"
  25
  26 \f
  27
  28 /* {Pairs}
  29  */
  30
  31 #if (SCM_DEBUG_PAIR_ACCESSES == 1)
  32
  33 #include "libguile/ports.h"
  34 #include "libguile/strings.h"
  35
  36 void scm_error_pair_access (SCM non_pair)
  37 {
  38   static unsigned int running = 0;
  39   SCM message = scm_from_locale_string ("Non-pair accessed with SCM_C[AD]R: `~S´\n");
  40
  41   if (!running)
  42     {
  43       running = 1;
  44       scm_simple_format (scm_current_error_port (),
  45                          message, scm_list_1 (non_pair));
  46       abort ();
  47     }
  48 }
  49
  50 #endif
  51
  52 SCM_DEFINE (scm_cons, "cons", 2, 0, 0,
  53             (SCM x, SCM y),
  54             "Return a newly allocated pair whose car is @var{x} and whose\n"
  55             "cdr is @var{y}.  The pair is guaranteed to be different (in the\n"
  56             "sense of @code{eq?}) from every previously existing object.")
  57 #define FUNC_NAME s_scm_cons
  58 {
  59   return scm_cell (SCM_UNPACK (x), SCM_UNPACK (y));
  60 }
  61 #undef FUNC_NAME
  62
  63
  64 SCM
  65 scm_cons2 (SCM w, SCM x, SCM y)
  66 {
  67   return scm_cons (w, scm_cons (x, y));
  68 }
  69
  70
  71 SCM_DEFINE (scm_pair_p, "pair?", 1, 0, 0,
  72             (SCM x),
  73             "Return @code{#t} if @var{x} is a pair; otherwise return\n"
  74             "@code{#f}.")
  75 #define FUNC_NAME s_scm_pair_p
  76 {
  77   return scm_from_bool (scm_is_pair (x));
  78 }
  79 #undef FUNC_NAME
  80
  81 int
  82 scm_is_pair (SCM x)
  83 {
  84   return SCM_I_CONSP (x);
  85 }
  86
  87 SCM
  88 scm_car (SCM pair)
  89 {
  90   if (!scm_is_pair (pair))
  91     scm_wrong_type_arg_msg (NULL, 0, pair, "pair");
  92   return SCM_CAR (pair);
  93 }
  94
  95 SCM
  96 scm_cdr (SCM pair)
  97 {
  98   if (!scm_is_pair (pair))
  99     scm_wrong_type_arg_msg (NULL, 0, pair, "pair");
 100   return SCM_CDR (pair);
 101 }
 102
 103 SCM
 104 scm_i_chase_pairs (SCM tree, scm_t_uint32 pattern)
 105 {
 106   do
 107     {
 108       if (!scm_is_pair (tree))
 109         scm_wrong_type_arg_msg (NULL, 0, tree, "pair");
 110       tree = (pattern & 1) ? SCM_CAR (tree) : SCM_CDR (tree);
 111       pattern >>= 2;
 112     }
 113   while (pattern);
 114   return tree;
 115 }
 116
 117 SCM_DEFINE (scm_set_car_x, "set-car!", 2, 0, 0,
 118             (SCM pair, SCM value),
 119             "Stores @var{value} in the car field of @var{pair}.  The value returned\n"
 120             "by @code{set-car!} is unspecified.")
 121 #define FUNC_NAME s_scm_set_car_x
 122 {
 123   SCM_VALIDATE_CONS (1, pair);
 124   SCM_SETCAR (pair, value);
 125   return SCM_UNSPECIFIED;
 126 }
 127 #undef FUNC_NAME
 128
 129
 130 SCM_DEFINE (scm_set_cdr_x, "set-cdr!", 2, 0, 0,
 131             (SCM pair, SCM value),
 132             "Stores @var{value} in the cdr field of @var{pair}.  The value returned\n"
 133             "by @code{set-cdr!} is unspecified.")
 134 #define FUNC_NAME s_scm_set_cdr_x
 135 {
 136   SCM_VALIDATE_CONS (1, pair);
 137   SCM_SETCDR (pair, value);
 138   return SCM_UNSPECIFIED;
 139 }
 140 #undef FUNC_NAME
 141
 142 \f
 143
 144 /* Every cxr-pattern is made up of pairs of bits, starting with the two least
 145  * significant bits.  If in a pair of bits the least significant of the two
 146  * bits is 0, this means CDR, otherwise CAR.  The most significant bits of the
 147  * two bits is only needed to indicate when cxr-ing is ready.  This is the
 148  * case, when all remaining pairs of bits equal 00.  */
 149
 150 typedef struct {
 151   const char *name;
 152   unsigned char pattern;
 153 } t_cxr;
 154
 155 static const t_cxr cxrs[] =
 156 {
 157   {"cdr",    0x02}, /* 00000010 */
 158   {"car",    0x03}, /* 00000011 */
 159   {"cddr",   0x0a}, /* 00001010 */
 160   {"cdar",   0x0b}, /* 00001011 */
 161   {"cadr",   0x0e}, /* 00001110 */
 162   {"caar",   0x0f}, /* 00001111 */
 163   {"cdddr",  0x2a}, /* 00101010 */
 164   {"cddar",  0x2b}, /* 00101011 */
 165   {"cdadr",  0x2e}, /* 00101110 */
 166   {"cdaar",  0x2f}, /* 00101111 */
 167   {"caddr",  0x3a}, /* 00111010 */
 168   {"cadar",  0x3b}, /* 00111011 */
 169   {"caadr",  0x3e}, /* 00111110 */
 170   {"caaar",  0x3f}, /* 00111111 */
 171   {"cddddr", 0xaa}, /* 10101010 */
 172   {"cdddar", 0xab}, /* 10101011 */
 173   {"cddadr", 0xae}, /* 10101110 */
 174   {"cddaar", 0xaf}, /* 10101111 */
 175   {"cdaddr", 0xba}, /* 10111010 */
 176   {"cdadar", 0xbb}, /* 10111011 */
 177   {"cdaadr", 0xbe}, /* 10111110 */
 178   {"cdaaar", 0xbf}, /* 10111111 */
 179   {"cadddr", 0xea}, /* 11101010 */
 180   {"caddar", 0xeb}, /* 11101011 */
 181   {"cadadr", 0xee}, /* 11101110 */
 182   {"cadaar", 0xef}, /* 11101111 */
 183   {"caaddr", 0xfa}, /* 11111010 */
 184   {"caadar", 0xfb}, /* 11111011 */
 185   {"caaadr", 0xfe}, /* 11111110 */
 186   {"caaaar", 0xff}, /* 11111111 */
 187   {0, 0}
 188 };
 189
 190 \f
 191
 192 void
 193 scm_init_pairs ()
 194 {
 195   unsigned int subnr = 0;
 196
 197   for (subnr = 0; cxrs[subnr].name; subnr++)
 198     {
 199       SCM (*pattern) () = (SCM (*) ()) (scm_t_bits) cxrs[subnr].pattern;
 200       scm_c_define_subr (cxrs[subnr].name, scm_tc7_cxr, pattern);
 201     }
 202
 203 #include "libguile/pairs.x"
 204 }
 205
 206
 207 /*
 208   Local Variables:
 209   c-file-style: "gnu"
 210   End:
 211 */