libguile/dynwind.c

   1 /* Copyright (C) 1995,1996,1998,1999,2000,2001 Free Software Foundation, Inc.
   2  *
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   7  *
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  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  11  * GNU General Public License for more details.
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  17  *
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  19  * for additional uses of the text contained in its release of GUILE.
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  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 "libguile/_scm.h"
  48 #include "libguile/eval.h"
  49 #include "libguile/alist.h"
  50 #include "libguile/fluids.h"
  51 #include "libguile/ports.h"
  52 #include "libguile/smob.h"
  53
  54 #include "libguile/dynwind.h"
  55 \f
  56
  57 /* {Dynamic wind}
  58
  59    Things that can be on the wind list:
  60
  61    (enter-proc . leave-proc)     dynamic-wind
  62    (tag . jmpbuf)                catch
  63    (tag . lazy-catch)            lazy-catch
  64      tag is either a symbol or a boolean
  65
  66    ((fluid ...) . (value ...))   with-fluids
  67
  68 */
  69
  70
  71
  72 SCM_DEFINE (scm_dynamic_wind, "dynamic-wind", 3, 0, 0,
  73            (SCM in_guard, SCM thunk, SCM out_guard),
  74             "All three arguments must be 0-argument procedures.\n"
  75             "@var{in_guard} is called, then @var{thunk}, then\n"
  76             "@var{out_guard}.\n"
  77             "\n"
  78             "If, any time during the execution of @var{thunk}, the\n"
  79             "continuation of the @code{dynamic_wind} expression is escaped\n"
  80             "non-locally, @var{out_guard} is called.  If the continuation of\n"
  81             "the dynamic-wind is re-entered, @var{in_guard} is called.  Thus\n"
  82             "@var{in_guard} and @var{out_guard} may be called any number of\n"
  83             "times.\n"
  84             "@lisp\n"
  85             "(define x 'normal-binding)\n"
  86             "@result{} x\n"
  87             "(define a-cont  (call-with-current-continuation \n"
  88             "             (lambda (escape)\n"
  89             "                (let ((old-x x))\n"
  90             "                  (dynamic-wind\n"
  91             "                     ;; in-guard:\n"
  92             "                     ;;\n"
  93             "                     (lambda () (set! x 'special-binding))\n"
  94             "\n"
  95             "                     ;; thunk\n"
  96             "                     ;;\n"
  97             "                     (lambda () (display x) (newline)\n"
  98             "                                (call-with-current-continuation escape)\n"
  99             "                                (display x) (newline)\n"
 100             "                                x)\n"
 101             "\n"
 102             "                     ;; out-guard:\n"
 103             "                     ;;\n"
 104             "                     (lambda () (set! x old-x)))))))\n"
 105             "\n"
 106             ";; Prints: \n"
 107             "special-binding\n"
 108             ";; Evaluates to:\n"
 109             "@result{} a-cont\n"
 110             "x\n"
 111             "@result{} normal-binding\n"
 112             "(a-cont #f)\n"
 113             ";; Prints:\n"
 114             "special-binding\n"
 115             ";; Evaluates to:\n"
 116             "@result{} a-cont  ;; the value of the (define a-cont...)\n"
 117             "x\n"
 118             "@result{} normal-binding\n"
 119             "a-cont\n"
 120             "@result{} special-binding\n"
 121             "@end lisp")
 122 #define FUNC_NAME s_scm_dynamic_wind
 123 {
 124   SCM ans;
 125   SCM_ASSERT (SCM_NFALSEP (scm_thunk_p (out_guard)),
 126               out_guard,
 127               SCM_ARG3, FUNC_NAME);
 128   scm_apply (in_guard, SCM_EOL, SCM_EOL);
 129   scm_dynwinds = scm_acons (in_guard, out_guard, scm_dynwinds);
 130   ans = scm_apply (thunk, SCM_EOL, SCM_EOL);
 131   scm_dynwinds = SCM_CDR (scm_dynwinds);
 132   scm_apply (out_guard, SCM_EOL, SCM_EOL);
 133   return ans;
 134 }
 135 #undef FUNC_NAME
 136
 137 /* The implementation of a C-callable dynamic-wind,
 138  * scm_internal_dynamic_wind, requires packaging of C pointers in a
 139  * smob.  Objects of this type are pushed onto the dynwind chain.
 140  */
 141
 142 #define SCM_GUARDSP(obj) SCM_TYP16_PREDICATE (tc16_guards, obj)
 143 #define SCM_BEFORE_GUARD(obj) ((scm_guard_t) SCM_CELL_WORD (obj, 1))
 144 #define SCM_AFTER_GUARD(obj) ((scm_guard_t) SCM_CELL_WORD (obj, 2))
 145 #define SCM_GUARD_DATA(obj) ((void *) SCM_CELL_WORD (obj, 3))
 146
 147 static scm_bits_t tc16_guards;
 148
 149 static int
 150 guards_print (SCM exp, SCM port, scm_print_state *pstate SCM_UNUSED)
 151 {
 152   scm_puts ("#<guards ", port);
 153   scm_intprint (SCM_UNPACK (SCM_CDR (exp)), 16, port);
 154   scm_putc ('>', port);
 155   return 1;
 156 }
 157
 158 SCM
 159 scm_internal_dynamic_wind (scm_guard_t before,
 160                            scm_inner_t inner,
 161                            scm_guard_t after,
 162                            void *inner_data,
 163                            void *guard_data)
 164 {
 165   SCM guards, ans;
 166   before (guard_data);
 167   SCM_NEWSMOB3 (guards, tc16_guards, (scm_bits_t) before,
 168                 (scm_bits_t) after, (scm_bits_t) guard_data);
 169   scm_dynwinds = scm_acons (guards, SCM_BOOL_F, scm_dynwinds);
 170   ans = inner (inner_data);
 171   scm_dynwinds = SCM_CDR (scm_dynwinds);
 172   after (guard_data);
 173   return ans;
 174 }
 175
 176 #ifdef GUILE_DEBUG
 177 SCM_DEFINE (scm_wind_chain, "wind-chain", 0, 0, 0,
 178             (),
 179             "Return the current wind chain. The wind chain contains all\n"
 180             "information required by @code{dynamic-wind} to call its\n"
 181             "argument thunks when entering/exiting its scope.")
 182 #define FUNC_NAME s_scm_wind_chain
 183 {
 184   return scm_dynwinds;
 185 }
 186 #undef FUNC_NAME
 187 #endif
 188
 189 static void
 190 scm_swap_bindings (SCM glocs, SCM vals)
 191 {
 192   SCM tmp;
 193   while (SCM_NIMP (vals))
 194     {
 195       tmp = SCM_GLOC_VAL (SCM_CAR (glocs));
 196       SCM_GLOC_SET_VAL (SCM_CAR (glocs), SCM_CAR (vals));
 197       SCM_SETCAR (vals, tmp);
 198       glocs = SCM_CDR (glocs);
 199       vals = SCM_CDR (vals);
 200     }
 201 }
 202
 203 void
 204 scm_dowinds (SCM to, long delta)
 205 {
 206  tail:
 207   if (SCM_EQ_P (to, scm_dynwinds));
 208   else if (delta < 0)
 209     {
 210       SCM wind_elt;
 211       SCM wind_key;
 212
 213       scm_dowinds (SCM_CDR (to), 1 + delta);
 214       wind_elt = SCM_CAR (to);
 215 #if 0
 216       if (SCM_INUMP (wind_elt))
 217         {
 218           scm_cross_dynwind_binding_scope (wind_elt, 0);
 219         }
 220       else
 221 #endif
 222         {
 223           wind_key = SCM_CAR (wind_elt);
 224           /* key = #t | symbol | thunk | list of glocs | list of fluids */
 225           if (SCM_NIMP (wind_key))
 226             {
 227               if (SCM_TYP3 (wind_key) == scm_tc3_cons_gloc)
 228                 scm_swap_bindings (wind_key, SCM_CDR (wind_elt));
 229               else if (SCM_TYP3 (wind_key) == scm_tc3_cons)
 230                 scm_swap_fluids (wind_key, SCM_CDR (wind_elt));
 231               else if (SCM_GUARDSP (wind_key))
 232                 SCM_BEFORE_GUARD (wind_key) (SCM_GUARD_DATA (wind_key));
 233               else if (SCM_TYP3 (wind_key) == scm_tc3_closure)
 234                 scm_apply (wind_key, SCM_EOL, SCM_EOL);
 235             }
 236         }
 237       scm_dynwinds = to;
 238     }
 239   else
 240     {
 241       SCM from;
 242       SCM wind_elt;
 243       SCM wind_key;
 244
 245       from = SCM_CDR (SCM_CAR (scm_dynwinds));
 246       wind_elt = SCM_CAR (scm_dynwinds);
 247       scm_dynwinds = SCM_CDR (scm_dynwinds);
 248 #if 0
 249       if (SCM_INUMP (wind_elt))
 250         {
 251           scm_cross_dynwind_binding_scope (wind_elt, 0);
 252         }
 253       else
 254 #endif
 255         {
 256           wind_key = SCM_CAR (wind_elt);
 257           if (SCM_NIMP (wind_key))
 258             {
 259               if (SCM_TYP3 (wind_key) == scm_tc3_cons_gloc)
 260                 scm_swap_bindings (wind_key, from);
 261               else if (SCM_TYP3 (wind_key) == scm_tc3_cons)
 262                 scm_swap_fluids_reverse (wind_key, from);
 263               else if (SCM_GUARDSP (wind_key))
 264                 SCM_AFTER_GUARD (wind_key) (SCM_GUARD_DATA (wind_key));
 265               else if (SCM_TYP3 (wind_key) == scm_tc3_closure)
 266                 scm_apply (from, SCM_EOL, SCM_EOL);
 267             }
 268         }
 269       delta--;
 270       goto tail;                /* scm_dowinds(to, delta-1); */
 271     }
 272 }
 273
 274
 275
 276 void
 277 scm_init_dynwind ()
 278 {
 279   tc16_guards = scm_make_smob_type ("guards", 0);
 280   scm_set_smob_print (tc16_guards, guards_print);
 281 #ifndef SCM_MAGIC_SNARFER
 282 #include "libguile/dynwind.x"
 283 #endif
 284 }
 285
 286 /*
 287   Local Variables:
 288   c-file-style: "gnu"
 289   End:
 290 */