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,
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  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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  29  *
  30  * This exception applies only to the code released by the
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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.
  76
  77 @var{in-guard} is called, then @var{thunk}, then @var{out-guard}.
  78
  79 If, any time during the execution of @var{thunk}, the continuation
  80 of the @code{dynamic-wind} expression is escaped non-locally, @var{out-guard}
  81 is called.   If the continuation of the dynamic-wind is re-entered,
  82 @var{in-guard} is called.   Thus @var{in-guard} and @var{out-guard} may
  83 be called any number of times.
  84
  85 @example
  86 (define x 'normal-binding)
  87 @result{} x
  88
  89 (define a-cont  (call-with-current-continuation
  90                   (lambda (escape)
  91                      (let ((old-x x))
  92                        (dynamic-wind
  93                           ;; in-guard:
  94                           ;;
  95                           (lambda () (set! x 'special-binding))
  96
  97                           ;; thunk
  98                           ;;
  99                           (lambda () (display x) (newline)
 100                                      (call-with-current-continuation escape)
 101                                      (display x) (newline)
 102                                      x)
 103
 104                           ;; out-guard:
 105                           ;;
 106                           (lambda () (set! x old-x)))))))
 107
 108 ;; Prints:
 109 special-binding
 110 ;; Evaluates to:
 111 @result{} a-cont
 112
 113 x
 114 @result{} normal-binding
 115
 116 (a-cont #f)
 117 ;; Prints:
 118 special-binding
 119 ;; Evaluates to:
 120 @result{} a-cont  ;; the value of the (define a-cont...)
 121
 122 x
 123 @result{} normal-binding
 124
 125 a-cont
 126 @result{} special-binding
 127 @end example
 128 ")
 129 #define FUNC_NAME s_scm_dynamic_wind
 130 {
 131   SCM ans;
 132   SCM_ASSERT (SCM_NFALSEP (scm_thunk_p (thunk3)),
 133               thunk3,
 134               SCM_ARG3, FUNC_NAME);
 135   scm_apply (thunk1, SCM_EOL, SCM_EOL);
 136   scm_dynwinds = scm_acons (thunk1, thunk3, scm_dynwinds);
 137   ans = scm_apply (thunk2, SCM_EOL, SCM_EOL);
 138   scm_dynwinds = SCM_CDR (scm_dynwinds);
 139   scm_apply (thunk3, SCM_EOL, SCM_EOL);
 140   return ans;
 141 }
 142 #undef FUNC_NAME
 143
 144 /* The implementation of a C-callable dynamic-wind,
 145  * scm_internal_dynamic_wind, requires packaging of C pointers in a
 146  * smob.  Objects of this type are pushed onto the dynwind chain.
 147  */
 148
 149 typedef struct guardsmem {
 150   scm_guard_t before;
 151   scm_guard_t after;
 152   void *data;
 153 } guardsmem;
 154
 155 #define SCM_GUARDSMEM(obj) ((guardsmem *) SCM_CDR (obj))
 156 #define SCM_BEFORE_GUARD(obj) (SCM_GUARDSMEM (obj)->before)
 157 #define SCM_AFTER_GUARD(obj) (SCM_GUARDSMEM (obj)->after)
 158 #define SCM_GUARD_DATA(obj) (SCM_GUARDSMEM (obj)->data)
 159 #define SCM_GUARDSP(obj) (SCM_NIMP(obj) && (SCM_CAR (obj) == tc16_guards))
 160
 161 static long tc16_guards;
 162
 163 static scm_sizet
 164 freeguards (SCM guards)
 165 {
 166   scm_must_free ((char *) SCM_CDR (guards));
 167   return sizeof (guardsmem);
 168 }
 169
 170 static int
 171 printguards (SCM exp, SCM port, scm_print_state *pstate)
 172 {
 173   scm_puts ("#<guards ", port);
 174   scm_intprint (SCM_CDR (exp), 16, port);
 175   scm_putc ('>', port);
 176   return 1;
 177 }
 178
 179 SCM
 180 scm_internal_dynamic_wind (scm_guard_t before,
 181                            scm_inner_t inner,
 182                            scm_guard_t after,
 183                            void *inner_data,
 184                            void *guard_data)
 185 {
 186   SCM guards, ans;
 187   guardsmem *g;
 188   before (guard_data);
 189   g = (guardsmem *) scm_must_malloc (sizeof (*g), "guards");
 190   g->before = before;
 191   g->after = after;
 192   g->data = guard_data;
 193   SCM_NEWSMOB (guards, tc16_guards, g);
 194   scm_dynwinds = scm_acons (guards, SCM_BOOL_F, scm_dynwinds);
 195   ans = inner (inner_data);
 196   scm_dynwinds = SCM_CDR (scm_dynwinds);
 197   after (guard_data);
 198   return ans;
 199 }
 200
 201 #ifdef GUILE_DEBUG
 202 SCM_DEFINE (scm_wind_chain, "wind-chain", 0, 0, 0,
 203             (),
 204 "")
 205 #define FUNC_NAME s_scm_wind_chain
 206 {
 207   return scm_dynwinds;
 208 }
 209 #undef FUNC_NAME
 210 #endif
 211
 212 static void
 213 scm_swap_bindings (SCM glocs, SCM vals)
 214 {
 215   SCM tmp;
 216   while (SCM_NIMP (vals))
 217     {
 218       tmp = SCM_GLOC_VAL (SCM_CAR (glocs));
 219       SCM_SETCDR (SCM_CAR (glocs) - 1L, SCM_CAR (vals));
 220       SCM_SETCAR (vals, tmp);
 221       glocs = SCM_CDR (glocs);
 222       vals = SCM_CDR (vals);
 223     }
 224 }
 225
 226 void
 227 scm_dowinds (SCM to, long delta)
 228 {
 229  tail:
 230   if (scm_dynwinds == to);
 231   else if (0 > delta)
 232     {
 233       SCM wind_elt;
 234       SCM wind_key;
 235
 236       scm_dowinds (SCM_CDR (to), 1 + delta);
 237       wind_elt = SCM_CAR (to);
 238 #if 0
 239       if (SCM_INUMP (wind_elt))
 240         {
 241           scm_cross_dynwind_binding_scope (wind_elt, 0);
 242         }
 243       else
 244 #endif
 245         {
 246           wind_key = SCM_CAR (wind_elt);
 247           /* key = #t | symbol | thunk | list of glocs | list of fluids */
 248           if (SCM_NIMP (wind_key))
 249             {
 250               if (SCM_TYP3 (wind_key) == scm_tc3_cons_gloc)
 251                 scm_swap_bindings (wind_key, SCM_CDR (wind_elt));
 252               else if (SCM_TYP3 (wind_key) == scm_tc3_cons)
 253                 scm_swap_fluids (wind_key, SCM_CDR (wind_elt));
 254               else if (SCM_GUARDSP (wind_key))
 255                 SCM_BEFORE_GUARD (wind_key) (SCM_GUARD_DATA (wind_key));
 256               else if (SCM_TYP3 (wind_key) == scm_tc3_closure)
 257                 scm_apply (wind_key, SCM_EOL, SCM_EOL);
 258             }
 259         }
 260       scm_dynwinds = to;
 261     }
 262   else
 263     {
 264       SCM from;
 265       SCM wind_elt;
 266       SCM wind_key;
 267
 268       from = SCM_CDR (SCM_CAR (scm_dynwinds));
 269       wind_elt = SCM_CAR (scm_dynwinds);
 270       scm_dynwinds = SCM_CDR (scm_dynwinds);
 271 #if 0
 272       if (SCM_INUMP (wind_elt))
 273         {
 274           scm_cross_dynwind_binding_scope (wind_elt, 0);
 275         }
 276       else
 277 #endif
 278         {
 279           wind_key = SCM_CAR (wind_elt);
 280           if (SCM_NIMP (wind_key))
 281             {
 282               if (SCM_TYP3 (wind_key) == scm_tc3_cons_gloc)
 283                 scm_swap_bindings (wind_key, from);
 284               else if (SCM_TYP3 (wind_key) == scm_tc3_cons)
 285                 scm_swap_fluids_reverse (wind_key, from);
 286               else if (SCM_GUARDSP (wind_key))
 287                 SCM_AFTER_GUARD (wind_key) (SCM_GUARD_DATA (wind_key));
 288               else if (SCM_TYP3 (wind_key) == scm_tc3_closure)
 289                 scm_apply (from, SCM_EOL, SCM_EOL);
 290             }
 291         }
 292       delta--;
 293       goto tail;                /* scm_dowinds(to, delta-1); */
 294     }
 295 }
 296
 297
 298
 299 void
 300 scm_init_dynwind ()
 301 {
 302   tc16_guards = scm_make_smob_type_mfpe ("guards", sizeof (struct guardsmem),
 303                                         NULL, freeguards, printguards, NULL);
 304 #include "dynwind.x"
 305 }