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.
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  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 "libguile/_scm.h"
  49 #include "libguile/eval.h"
  50 #include "libguile/alist.h"
  51 #include "libguile/fluids.h"
  52 #include "libguile/ports.h"
  53 #include "libguile/smob.h"
  54
  55 #include "libguile/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 #define FUNC_NAME s_scm_dynamic_wind
 118 {
 119   SCM ans;
 120   SCM_ASSERT (SCM_NFALSEP (scm_thunk_p (thunk3)),
 121               thunk3,
 122               SCM_ARG3, FUNC_NAME);
 123   scm_apply (thunk1, SCM_EOL, SCM_EOL);
 124   scm_dynwinds = scm_acons (thunk1, thunk3, scm_dynwinds);
 125   ans = scm_apply (thunk2, SCM_EOL, SCM_EOL);
 126   scm_dynwinds = SCM_CDR (scm_dynwinds);
 127   scm_apply (thunk3, SCM_EOL, SCM_EOL);
 128   return ans;
 129 }
 130 #undef FUNC_NAME
 131
 132 /* The implementation of a C-callable dynamic-wind,
 133  * scm_internal_dynamic_wind, requires packaging of C pointers in a
 134  * smob.  Objects of this type are pushed onto the dynwind chain.
 135  */
 136
 137 #define SCM_GUARDSP(obj) SCM_TYP16_PREDICATE (tc16_guards, obj)
 138 #define SCM_BEFORE_GUARD(obj) ((scm_guard_t) SCM_CELL_WORD (obj, 1))
 139 #define SCM_AFTER_GUARD(obj) ((scm_guard_t) SCM_CELL_WORD (obj, 2))
 140 #define SCM_GUARD_DATA(obj) ((void *) SCM_CELL_WORD (obj, 3))
 141
 142 static scm_bits_t tc16_guards;
 143
 144 static int
 145 guards_print (SCM exp, SCM port, scm_print_state *pstate)
 146 {
 147   scm_puts ("#<guards ", port);
 148   scm_intprint (SCM_UNPACK (SCM_CDR (exp)), 16, port);
 149   scm_putc ('>', port);
 150   return 1;
 151 }
 152
 153 SCM
 154 scm_internal_dynamic_wind (scm_guard_t before,
 155                            scm_inner_t inner,
 156                            scm_guard_t after,
 157                            void *inner_data,
 158                            void *guard_data)
 159 {
 160   SCM guards, ans;
 161   before (guard_data);
 162   SCM_NEWSMOB3 (guards, tc16_guards, (scm_bits_t) before,
 163                 (scm_bits_t) after, (scm_bits_t) guard_data);
 164   scm_dynwinds = scm_acons (guards, SCM_BOOL_F, scm_dynwinds);
 165   ans = inner (inner_data);
 166   scm_dynwinds = SCM_CDR (scm_dynwinds);
 167   after (guard_data);
 168   return ans;
 169 }
 170
 171 #ifdef GUILE_DEBUG
 172 SCM_DEFINE (scm_wind_chain, "wind-chain", 0, 0, 0,
 173             (),
 174             "Return the current wind chain. The wind chain contains all\n"
 175             "information required by @code{dynamic-wind} to call its\n"
 176             "argument thunks when entering/exiting its scope.")
 177 #define FUNC_NAME s_scm_wind_chain
 178 {
 179   return scm_dynwinds;
 180 }
 181 #undef FUNC_NAME
 182 #endif
 183
 184 static void
 185 scm_swap_bindings (SCM glocs, SCM vals)
 186 {
 187   SCM tmp;
 188   while (SCM_NIMP (vals))
 189     {
 190       tmp = SCM_GLOC_VAL (SCM_CAR (glocs));
 191       SCM_SETCDR (SCM_PACK (SCM_UNPACK (SCM_CAR (glocs)) - 1L),
 192                   SCM_CAR (vals));
 193       SCM_SETCAR (vals, tmp);
 194       glocs = SCM_CDR (glocs);
 195       vals = SCM_CDR (vals);
 196     }
 197 }
 198
 199 void
 200 scm_dowinds (SCM to, long delta)
 201 {
 202  tail:
 203   if (SCM_EQ_P (to, scm_dynwinds));
 204   else if (0 > delta)
 205     {
 206       SCM wind_elt;
 207       SCM wind_key;
 208
 209       scm_dowinds (SCM_CDR (to), 1 + delta);
 210       wind_elt = SCM_CAR (to);
 211 #if 0
 212       if (SCM_INUMP (wind_elt))
 213         {
 214           scm_cross_dynwind_binding_scope (wind_elt, 0);
 215         }
 216       else
 217 #endif
 218         {
 219           wind_key = SCM_CAR (wind_elt);
 220           /* key = #t | symbol | thunk | list of glocs | list of fluids */
 221           if (SCM_NIMP (wind_key))
 222             {
 223               if (SCM_TYP3 (wind_key) == scm_tc3_cons_gloc)
 224                 scm_swap_bindings (wind_key, SCM_CDR (wind_elt));
 225               else if (SCM_TYP3 (wind_key) == scm_tc3_cons)
 226                 scm_swap_fluids (wind_key, SCM_CDR (wind_elt));
 227               else if (SCM_GUARDSP (wind_key))
 228                 SCM_BEFORE_GUARD (wind_key) (SCM_GUARD_DATA (wind_key));
 229               else if (SCM_TYP3 (wind_key) == scm_tc3_closure)
 230                 scm_apply (wind_key, SCM_EOL, SCM_EOL);
 231             }
 232         }
 233       scm_dynwinds = to;
 234     }
 235   else
 236     {
 237       SCM from;
 238       SCM wind_elt;
 239       SCM wind_key;
 240
 241       from = SCM_CDR (SCM_CAR (scm_dynwinds));
 242       wind_elt = SCM_CAR (scm_dynwinds);
 243       scm_dynwinds = SCM_CDR (scm_dynwinds);
 244 #if 0
 245       if (SCM_INUMP (wind_elt))
 246         {
 247           scm_cross_dynwind_binding_scope (wind_elt, 0);
 248         }
 249       else
 250 #endif
 251         {
 252           wind_key = SCM_CAR (wind_elt);
 253           if (SCM_NIMP (wind_key))
 254             {
 255               if (SCM_TYP3 (wind_key) == scm_tc3_cons_gloc)
 256                 scm_swap_bindings (wind_key, from);
 257               else if (SCM_TYP3 (wind_key) == scm_tc3_cons)
 258                 scm_swap_fluids_reverse (wind_key, from);
 259               else if (SCM_GUARDSP (wind_key))
 260                 SCM_AFTER_GUARD (wind_key) (SCM_GUARD_DATA (wind_key));
 261               else if (SCM_TYP3 (wind_key) == scm_tc3_closure)
 262                 scm_apply (from, SCM_EOL, SCM_EOL);
 263             }
 264         }
 265       delta--;
 266       goto tail;                /* scm_dowinds(to, delta-1); */
 267     }
 268 }
 269
 270
 271
 272 void
 273 scm_init_dynwind ()
 274 {
 275   tc16_guards = scm_make_smob_type ("guards", 0);
 276   scm_set_smob_print (tc16_guards, guards_print);
 277 #ifndef SCM_MAGIC_SNARFER
 278 #include "libguile/dynwind.x"
 279 #endif
 280 }
 281
 282 /*
 283   Local Variables:
 284   c-file-style: "gnu"
 285   End:
 286 */