libguile/dynwind.c

   1 /*      Copyright (C) 1995, 1996, 1998, 1999, 2000 Free Software Foundation, Inc.
   2  *
   3  * This program is free software; you can redistribute it and/or modify
   4  * it under the terms of the GNU General Public License as published by
   5  * the Free Software Foundation; either version 2, or (at your option)
   6  * any later version.
   7  *
   8  * This program 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
  11  * GNU General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU General Public License
  14  * along with this software; see the file COPYING.  If not, write to
  15  * the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
  16  * Boston, MA 02111-1307 USA
  17  *
  18  * As a special exception, the Free Software Foundation gives permission
  19  * for additional uses of the text contained in its release of GUILE.
  20  *
  21  * The exception is that, if you link the GUILE library with other files
  22  * to produce an executable, this does not by itself cause the
  23  * resulting executable to be covered by the GNU General Public License.
  24  * Your use of that executable is in no way restricted on account of
  25  * linking the GUILE library code into it.
  26  *
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  28  * the executable file might be covered by the GNU General Public License.
  29  *
  30  * This exception applies only to the code released by the
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  37  *
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  39  * whether to permit this exception to apply to your modifications.
  40  * If you do not wish that, delete this exception notice.  */
  41
  42 /* Software engineering face-lift by Greg J. Badros, 11-Dec-1999,
  43    gjb@cs.washington.edu, http://www.cs.washington.edu/homes/gjb */
  44
  45 \f
  46
  47 #include <stdio.h>
  48 #include "_scm.h"
  49 #include "eval.h"
  50 #include "alist.h"
  51 #include "fluids.h"
  52 #include "ports.h"
  53 #include "smob.h"
  54
  55 #include "dynwind.h"
  56 \f
  57
  58 /* {Dynamic wind}
  59
  60    Things that can be on the wind list:
  61
  62    (enter-proc . leave-proc)     dynamic-wind
  63    (tag . jmpbuf)                catch
  64    (tag . lazy-catch)            lazy-catch
  65      tag is either a symbol or a boolean
  66
  67    ((fluid ...) . (value ...))   with-fluids
  68
  69 */
  70
  71
  72
  73 SCM_DEFINE (scm_dynamic_wind, "dynamic-wind", 3, 0, 0,
  74            (SCM thunk1, SCM thunk2, SCM thunk3),
  75             "All three arguments must be 0-argument procedures.\n\n"
  76             "@var{in-guard} is called, then @var{thunk}, then @var{out-guard}.\n\n"
  77             "If, any time during the execution of @var{thunk}, the continuation\n"
  78             "of the @code{dynamic-wind} expression is escaped non-locally, @var{out-guard}\n"
  79             "is called.   If the continuation of the dynamic-wind is re-entered,\n"
  80             "@var{in-guard} is called.   Thus @var{in-guard} and @var{out-guard} may\n"
  81             "be called any number of times.\n\n"
  82             "@example\n"
  83             "(define x 'normal-binding)\n"
  84             "@result{} x\n\n"
  85             "(define a-cont  (call-with-current-continuation \n"
  86             "             (lambda (escape)\n"
  87             "                (let ((old-x x))\n"
  88             "                  (dynamic-wind\n"
  89             "                     ;; in-guard:\n"
  90             "                     ;;\n"
  91             "                     (lambda () (set! x 'special-binding))\n\n"
  92             "                     ;; thunk\n"
  93             "                     ;;\n"
  94             "                     (lambda () (display x) (newline)\n"
  95             "                                (call-with-current-continuation escape)\n"
  96             "                                (display x) (newline)\n"
  97             "                                x)\n\n"
  98             "                     ;; out-guard:\n"
  99             "                     ;;\n"
 100             "                     (lambda () (set! x old-x)))))))\n\n"
 101             ";; Prints: \n"
 102             "special-binding\n"
 103             ";; Evaluates to:\n"
 104             "@result{} a-cont\n\n"
 105             "x\n"
 106             "@result{} normal-binding\n\n"
 107             "(a-cont #f)\n"
 108             ";; Prints:\n"
 109             "special-binding\n"
 110             ";; Evaluates to:\n"
 111             "@result{} a-cont  ;; the value of the (define a-cont...)\n\n"
 112             "x\n"
 113             "@result{} normal-binding\n\n"
 114             "a-cont\n"
 115             "@result{} special-binding\n"
 116             "@end example\n"
 117             "")
 118 #define FUNC_NAME s_scm_dynamic_wind
 119 {
 120   SCM ans;
 121   SCM_ASSERT (SCM_NFALSEP (scm_thunk_p (thunk3)),
 122               thunk3,
 123               SCM_ARG3, FUNC_NAME);
 124   scm_apply (thunk1, SCM_EOL, SCM_EOL);
 125   scm_dynwinds = scm_acons (thunk1, thunk3, scm_dynwinds);
 126   ans = scm_apply (thunk2, SCM_EOL, SCM_EOL);
 127   scm_dynwinds = SCM_CDR (scm_dynwinds);
 128   scm_apply (thunk3, SCM_EOL, SCM_EOL);
 129   return ans;
 130 }
 131 #undef FUNC_NAME
 132
 133 /* The implementation of a C-callable dynamic-wind,
 134  * scm_internal_dynamic_wind, requires packaging of C pointers in a
 135  * smob.  Objects of this type are pushed onto the dynwind chain.
 136  */
 137
 138 #define SCM_GUARDSP(obj) SCM_SMOB_PREDICATE (tc16_guards, obj)
 139 #define SCM_BEFORE_GUARD(obj) ((scm_guard_t) SCM_CELL_WORD (obj, 1))
 140 #define SCM_AFTER_GUARD(obj) ((scm_guard_t) SCM_CELL_WORD (obj, 2))
 141 #define SCM_GUARD_DATA(obj) ((void *) SCM_CELL_WORD (obj, 3))
 142
 143 static long tc16_guards;
 144
 145 static int
 146 printguards (SCM exp, SCM port, scm_print_state *pstate)
 147 {
 148   scm_puts ("#<guards ", port);
 149   scm_intprint (SCM_UNPACK (SCM_CDR (exp)), 16, port);
 150   scm_putc ('>', port);
 151   return 1;
 152 }
 153
 154 SCM
 155 scm_internal_dynamic_wind (scm_guard_t before,
 156                            scm_inner_t inner,
 157                            scm_guard_t after,
 158                            void *inner_data,
 159                            void *guard_data)
 160 {
 161   SCM guards, ans;
 162   before (guard_data);
 163   SCM_NEWSMOB3 (guards, tc16_guards, (scm_bits_t) before,
 164                 (scm_bits_t) after, (scm_bits_t) guard_data);
 165   scm_dynwinds = scm_acons (guards, SCM_BOOL_F, scm_dynwinds);
 166   ans = inner (inner_data);
 167   scm_dynwinds = SCM_CDR (scm_dynwinds);
 168   after (guard_data);
 169   return ans;
 170 }
 171
 172 #ifdef GUILE_DEBUG
 173 SCM_DEFINE (scm_wind_chain, "wind-chain", 0, 0, 0,
 174             (),
 175             "")
 176 #define FUNC_NAME s_scm_wind_chain
 177 {
 178   return scm_dynwinds;
 179 }
 180 #undef FUNC_NAME
 181 #endif
 182
 183 static void
 184 scm_swap_bindings (SCM glocs, SCM vals)
 185 {
 186   SCM tmp;
 187   while (SCM_NIMP (vals))
 188     {
 189       tmp = SCM_GLOC_VAL (SCM_CAR (glocs));
 190       SCM_SETCDR (SCM_PACK (SCM_UNPACK (SCM_CAR (glocs)) - 1L),
 191                   SCM_CAR (vals));
 192       SCM_SETCAR (vals, tmp);
 193       glocs = SCM_CDR (glocs);
 194       vals = SCM_CDR (vals);
 195     }
 196 }
 197
 198 void
 199 scm_dowinds (SCM to, long delta)
 200 {
 201  tail:
 202   if (SCM_EQ_P (to, scm_dynwinds));
 203   else if (0 > delta)
 204     {
 205       SCM wind_elt;
 206       SCM wind_key;
 207
 208       scm_dowinds (SCM_CDR (to), 1 + delta);
 209       wind_elt = SCM_CAR (to);
 210 #if 0
 211       if (SCM_INUMP (wind_elt))
 212         {
 213           scm_cross_dynwind_binding_scope (wind_elt, 0);
 214         }
 215       else
 216 #endif
 217         {
 218           wind_key = SCM_CAR (wind_elt);
 219           /* key = #t | symbol | thunk | list of glocs | list of fluids */
 220           if (SCM_NIMP (wind_key))
 221             {
 222               if (SCM_TYP3 (wind_key) == scm_tc3_cons_gloc)
 223                 scm_swap_bindings (wind_key, SCM_CDR (wind_elt));
 224               else if (SCM_TYP3 (wind_key) == scm_tc3_cons)
 225                 scm_swap_fluids (wind_key, SCM_CDR (wind_elt));
 226               else if (SCM_GUARDSP (wind_key))
 227                 SCM_BEFORE_GUARD (wind_key) (SCM_GUARD_DATA (wind_key));
 228               else if (SCM_TYP3 (wind_key) == scm_tc3_closure)
 229                 scm_apply (wind_key, SCM_EOL, SCM_EOL);
 230             }
 231         }
 232       scm_dynwinds = to;
 233     }
 234   else
 235     {
 236       SCM from;
 237       SCM wind_elt;
 238       SCM wind_key;
 239
 240       from = SCM_CDR (SCM_CAR (scm_dynwinds));
 241       wind_elt = SCM_CAR (scm_dynwinds);
 242       scm_dynwinds = SCM_CDR (scm_dynwinds);
 243 #if 0
 244       if (SCM_INUMP (wind_elt))
 245         {
 246           scm_cross_dynwind_binding_scope (wind_elt, 0);
 247         }
 248       else
 249 #endif
 250         {
 251           wind_key = SCM_CAR (wind_elt);
 252           if (SCM_NIMP (wind_key))
 253             {
 254               if (SCM_TYP3 (wind_key) == scm_tc3_cons_gloc)
 255                 scm_swap_bindings (wind_key, from);
 256               else if (SCM_TYP3 (wind_key) == scm_tc3_cons)
 257                 scm_swap_fluids_reverse (wind_key, from);
 258               else if (SCM_GUARDSP (wind_key))
 259                 SCM_AFTER_GUARD (wind_key) (SCM_GUARD_DATA (wind_key));
 260               else if (SCM_TYP3 (wind_key) == scm_tc3_closure)
 261                 scm_apply (from, SCM_EOL, SCM_EOL);
 262             }
 263         }
 264       delta--;
 265       goto tail;                /* scm_dowinds(to, delta-1); */
 266     }
 267 }
 268
 269
 270
 271 void
 272 scm_init_dynwind ()
 273 {
 274   tc16_guards = scm_make_smob_type_mfpe ("guards", 0,
 275                                          NULL, scm_free0, printguards, NULL);
 276 #include "dynwind.x"
 277 }
 278
 279 /*
 280   Local Variables:
 281   c-file-style: "gnu"
 282   End:
 283 */