libguile/dynwind.c

   1 /*      Copyright (C) 1995, 1996, 1998, 1999 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
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   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  *
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  25  * linking the GUILE library code into it.
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  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 "genio.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 typedef struct guardsmem {
 139   scm_guard_t before;
 140   scm_guard_t after;
 141   void *data;
 142 } guardsmem;
 143
 144 #define SCM_GUARDSMEM(obj) ((guardsmem *) SCM_CDR (obj))
 145 #define SCM_BEFORE_GUARD(obj) (SCM_GUARDSMEM (obj)->before)
 146 #define SCM_AFTER_GUARD(obj) (SCM_GUARDSMEM (obj)->after)
 147 #define SCM_GUARD_DATA(obj) (SCM_GUARDSMEM (obj)->data)
 148 #define SCM_GUARDSP(obj) (SCM_NIMP(obj) && (SCM_CAR (obj) == tc16_guards))
 149
 150 static long tc16_guards;
 151
 152 static scm_sizet
 153 freeguards (SCM guards)
 154 {
 155   scm_must_free ((char *) SCM_CDR (guards));
 156   return sizeof (guardsmem);
 157 }
 158
 159 static int
 160 printguards (SCM exp, SCM port, scm_print_state *pstate)
 161 {
 162   scm_puts ("#<guards ", port);
 163   scm_intprint (SCM_CDR (exp), 16, port);
 164   scm_putc ('>', port);
 165   return 1;
 166 }
 167
 168 SCM
 169 scm_internal_dynamic_wind (scm_guard_t before,
 170                            scm_inner_t inner,
 171                            scm_guard_t after,
 172                            void *inner_data,
 173                            void *guard_data)
 174 {
 175   SCM guards, ans;
 176   guardsmem *g;
 177   before (guard_data);
 178   g = (guardsmem *) scm_must_malloc (sizeof (*g), "guards");
 179   g->before = before;
 180   g->after = after;
 181   g->data = guard_data;
 182   SCM_NEWSMOB (guards, tc16_guards, g);
 183   scm_dynwinds = scm_acons (guards, SCM_BOOL_F, scm_dynwinds);
 184   ans = inner (inner_data);
 185   scm_dynwinds = SCM_CDR (scm_dynwinds);
 186   after (guard_data);
 187   return ans;
 188 }
 189
 190 #ifdef GUILE_DEBUG
 191 SCM_DEFINE (scm_wind_chain, "wind-chain", 0, 0, 0,
 192             (),
 193             "")
 194 #define FUNC_NAME s_scm_wind_chain
 195 {
 196   return scm_dynwinds;
 197 }
 198 #undef FUNC_NAME
 199 #endif
 200
 201 static void
 202 scm_swap_bindings (SCM glocs, SCM vals)
 203 {
 204   SCM tmp;
 205   while (SCM_NIMP (vals))
 206     {
 207       tmp = SCM_GLOC_VAL (SCM_CAR (glocs));
 208       SCM_SETCDR (SCM_CAR (glocs) - 1L, SCM_CAR (vals));
 209       SCM_SETCAR (vals, tmp);
 210       glocs = SCM_CDR (glocs);
 211       vals = SCM_CDR (vals);
 212     }
 213 }
 214
 215 void
 216 scm_dowinds (SCM to, long delta)
 217 {
 218  tail:
 219   if (scm_dynwinds == to);
 220   else if (0 > delta)
 221     {
 222       SCM wind_elt;
 223       SCM wind_key;
 224
 225       scm_dowinds (SCM_CDR (to), 1 + delta);
 226       wind_elt = SCM_CAR (to);
 227 #if 0
 228       if (SCM_INUMP (wind_elt))
 229         {
 230           scm_cross_dynwind_binding_scope (wind_elt, 0);
 231         }
 232       else
 233 #endif
 234         {
 235           wind_key = SCM_CAR (wind_elt);
 236           /* key = #t | symbol | thunk | list of glocs | list of fluids */
 237           if (SCM_NIMP (wind_key))
 238             {
 239               if (SCM_TYP3 (wind_key) == scm_tc3_cons_gloc)
 240                 scm_swap_bindings (wind_key, SCM_CDR (wind_elt));
 241               else if (SCM_TYP3 (wind_key) == scm_tc3_cons)
 242                 scm_swap_fluids (wind_key, SCM_CDR (wind_elt));
 243               else if (SCM_GUARDSP (wind_key))
 244                 SCM_BEFORE_GUARD (wind_key) (SCM_GUARD_DATA (wind_key));
 245               else if (SCM_TYP3 (wind_key) == scm_tc3_closure)
 246                 scm_apply (wind_key, SCM_EOL, SCM_EOL);
 247             }
 248         }
 249       scm_dynwinds = to;
 250     }
 251   else
 252     {
 253       SCM from;
 254       SCM wind_elt;
 255       SCM wind_key;
 256
 257       from = SCM_CDR (SCM_CAR (scm_dynwinds));
 258       wind_elt = SCM_CAR (scm_dynwinds);
 259       scm_dynwinds = SCM_CDR (scm_dynwinds);
 260 #if 0
 261       if (SCM_INUMP (wind_elt))
 262         {
 263           scm_cross_dynwind_binding_scope (wind_elt, 0);
 264         }
 265       else
 266 #endif
 267         {
 268           wind_key = SCM_CAR (wind_elt);
 269           if (SCM_NIMP (wind_key))
 270             {
 271               if (SCM_TYP3 (wind_key) == scm_tc3_cons_gloc)
 272                 scm_swap_bindings (wind_key, from);
 273               else if (SCM_TYP3 (wind_key) == scm_tc3_cons)
 274                 scm_swap_fluids_reverse (wind_key, from);
 275               else if (SCM_GUARDSP (wind_key))
 276                 SCM_AFTER_GUARD (wind_key) (SCM_GUARD_DATA (wind_key));
 277               else if (SCM_TYP3 (wind_key) == scm_tc3_closure)
 278                 scm_apply (from, SCM_EOL, SCM_EOL);
 279             }
 280         }
 281       delta--;
 282       goto tail;                /* scm_dowinds(to, delta-1); */
 283     }
 284 }
 285
 286
 287
 288 void
 289 scm_init_dynwind ()
 290 {
 291   tc16_guards = scm_make_smob_type_mfpe ("guards", sizeof (struct guardsmem),
 292                                         NULL, freeguards, printguards, NULL);
 293 #include "dynwind.x"
 294 }