gdb/guile/scm-iterator.c

   1 /* Simple iterators for GDB/Scheme.
   2
   3    Copyright (C) 2014-2021 Free Software Foundation, Inc.
   4
   5    This file is part of GDB.
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 3 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  19
  20 /* See README file in this directory for implementation notes, coding
  21    conventions, et.al.  */
  22
  23 /* These are *simple* iterators, used to implement iterating over a collection
  24    of objects.  They are implemented as a smob containing three objects:
  25
  26    1) the object being iterated over,
  27    2) an object to record the progress of the iteration,
  28    3) a procedure of one argument (the iterator object) that returns the next
  29       object in the iteration or a pre-determined end marker.
  30
  31    Simple example:
  32
  33    (define-public (make-list-iterator l end-marker)
  34      "Return a <gdb:iterator> object for a list."
  35      (let ((next! (lambda (iter)
  36                     (let ((l (iterator-progress iter)))
  37                       (if (eq? l '())
  38                           end-marker
  39                           (begin
  40                             (set-iterator-progress! iter (cdr l))
  41                             (car l)))))))
  42        (make-iterator l l next!)))
  43
  44    (define l '(1 2))
  45    (define i (make-list-iterator l #:eoi))
  46    (iterator-next! i) -> 1
  47    (iterator-next! i) -> 2
  48    (iterator-next! i) -> #:eoi
  49
  50    There is SRFI 41, Streams.  We might support that too eventually (not with
  51    this interface of course).  */
  52
  53 #include "defs.h"
  54 #include "guile-internal.h"
  55
  56 /* A smob for iterating over something.
  57    Typically this is used when computing a list of everything is
  58    too expensive.  */
  59
  60 struct iterator_smob
  61 {
  62   /* This always appears first.  */
  63   gdb_smob base;
  64
  65   /* The object being iterated over.  */
  66   SCM object;
  67
  68   /* An arbitrary object describing the progress of the iteration.
  69      This is used by next_x to track progress.  */
  70   SCM progress;
  71
  72   /* A procedure of one argument, the iterator.
  73      It returns the next object in the iteration.
  74      How to signal "end of iteration" is up to next_x.  */
  75   SCM next_x;
  76 };
  77
  78 static const char iterator_smob_name[] = "gdb:iterator";
  79
  80 /* The tag Guile knows the iterator smob by.  */
  81 static scm_t_bits iterator_smob_tag;
  82
  83 /* A unique-enough marker to denote "end of iteration".  */
  84 static SCM end_of_iteration;
  85
  86 const char *
  87 itscm_iterator_smob_name (void)
  88 {
  89   return iterator_smob_name;
  90 }
  91
  92 SCM
  93 itscm_iterator_smob_object (iterator_smob *i_smob)
  94 {
  95   return i_smob->object;
  96 }
  97
  98 SCM
  99 itscm_iterator_smob_progress (iterator_smob *i_smob)
 100 {
 101   return i_smob->progress;
 102 }
 103
 104 void
 105 itscm_set_iterator_smob_progress_x (iterator_smob *i_smob, SCM progress)
 106 {
 107   i_smob->progress = progress;
 108 }
 109 \f
 110 /* Administrivia for iterator smobs.  */
 111
 112 /* The smob "print" function for <gdb:iterator>.  */
 113
 114 static int
 115 itscm_print_iterator_smob (SCM self, SCM port, scm_print_state *pstate)
 116 {
 117   iterator_smob *i_smob = (iterator_smob *) SCM_SMOB_DATA (self);
 118
 119   gdbscm_printf (port, "#<%s ", iterator_smob_name);
 120   scm_write (i_smob->object, port);
 121   scm_puts (" ", port);
 122   scm_write (i_smob->progress, port);
 123   scm_puts (" ", port);
 124   scm_write (i_smob->next_x, port);
 125   scm_puts (">", port);
 126
 127   scm_remember_upto_here_1 (self);
 128
 129   /* Non-zero means success.  */
 130   return 1;
 131 }
 132
 133 /* Low level routine to make a <gdb:iterator> object.
 134    Caller must verify correctness of arguments.
 135    No exceptions are thrown.  */
 136
 137 static SCM
 138 itscm_make_iterator_smob (SCM object, SCM progress, SCM next)
 139 {
 140   iterator_smob *i_smob = (iterator_smob *)
 141     scm_gc_malloc (sizeof (iterator_smob), iterator_smob_name);
 142   SCM i_scm;
 143
 144   i_smob->object = object;
 145   i_smob->progress = progress;
 146   i_smob->next_x = next;
 147   i_scm = scm_new_smob (iterator_smob_tag, (scm_t_bits) i_smob);
 148   gdbscm_init_gsmob (&i_smob->base);
 149
 150   return i_scm;
 151 }
 152
 153 /* (make-iterator object object procedure) -> <gdb:iterator> */
 154
 155 SCM
 156 gdbscm_make_iterator (SCM object, SCM progress, SCM next)
 157 {
 158   SCM i_scm;
 159
 160   SCM_ASSERT_TYPE (gdbscm_is_procedure (next), next, SCM_ARG3, FUNC_NAME,
 161                    _("procedure"));
 162
 163   i_scm = itscm_make_iterator_smob (object, progress, next);
 164
 165   return i_scm;
 166 }
 167
 168 /* Return non-zero if SCM is a <gdb:iterator> object.  */
 169
 170 int
 171 itscm_is_iterator (SCM scm)
 172 {
 173   return SCM_SMOB_PREDICATE (iterator_smob_tag, scm);
 174 }
 175
 176 /* (iterator? object) -> boolean */
 177
 178 static SCM
 179 gdbscm_iterator_p (SCM scm)
 180 {
 181   return scm_from_bool (itscm_is_iterator (scm));
 182 }
 183
 184 /* (end-of-iteration) -> an "end-of-iteration" marker
 185    We rely on this not being used as a data result of an iterator.  */
 186
 187 SCM
 188 gdbscm_end_of_iteration (void)
 189 {
 190   return end_of_iteration;
 191 }
 192
 193 /* Return non-zero if OBJ is the end-of-iteration marker.  */
 194
 195 int
 196 itscm_is_end_of_iteration (SCM obj)
 197 {
 198   return scm_is_eq (obj, end_of_iteration);
 199 }
 200
 201 /* (end-of-iteration? obj) -> boolean */
 202
 203 static SCM
 204 gdbscm_end_of_iteration_p (SCM obj)
 205 {
 206   return scm_from_bool (itscm_is_end_of_iteration (obj));
 207 }
 208
 209 /* Call the next! method on ITER, which must be a <gdb:iterator> object.
 210    Returns a <gdb:exception> object if an exception is thrown.
 211    OK_EXCPS is passed to gdbscm_safe_call_1.  */
 212
 213 SCM
 214 itscm_safe_call_next_x (SCM iter, excp_matcher_func *ok_excps)
 215 {
 216   iterator_smob *i_smob;
 217
 218   gdb_assert (itscm_is_iterator (iter));
 219
 220   i_smob = (iterator_smob *) SCM_SMOB_DATA (iter);
 221   return gdbscm_safe_call_1 (i_smob->next_x, iter, ok_excps);
 222 }
 223 \f
 224 /* Iterator methods.  */
 225
 226 /* Returns the <gdb:iterator> smob in SELF.
 227    Throws an exception if SELF is not an iterator smob.  */
 228
 229 SCM
 230 itscm_get_iterator_arg_unsafe (SCM self, int arg_pos, const char *func_name)
 231 {
 232   SCM_ASSERT_TYPE (itscm_is_iterator (self), self, arg_pos, func_name,
 233                    iterator_smob_name);
 234
 235   return self;
 236 }
 237
 238 /* (iterator-object <gdb:iterator>) -> object */
 239
 240 static SCM
 241 gdbscm_iterator_object (SCM self)
 242 {
 243   SCM i_scm;
 244   iterator_smob *i_smob;
 245
 246   i_scm = itscm_get_iterator_arg_unsafe (self, SCM_ARG1, FUNC_NAME);
 247   i_smob = (iterator_smob *) SCM_SMOB_DATA (i_scm);
 248
 249   return i_smob->object;
 250 }
 251
 252 /* (iterator-progress <gdb:iterator>) -> object */
 253
 254 static SCM
 255 gdbscm_iterator_progress (SCM self)
 256 {
 257   SCM i_scm;
 258   iterator_smob *i_smob;
 259
 260   i_scm = itscm_get_iterator_arg_unsafe (self, SCM_ARG1, FUNC_NAME);
 261   i_smob = (iterator_smob *) SCM_SMOB_DATA (i_scm);
 262
 263   return i_smob->progress;
 264 }
 265
 266 /* (set-iterator-progress! <gdb:iterator> object) -> unspecified */
 267
 268 static SCM
 269 gdbscm_set_iterator_progress_x (SCM self, SCM value)
 270 {
 271   SCM i_scm;
 272   iterator_smob *i_smob;
 273
 274   i_scm = itscm_get_iterator_arg_unsafe (self, SCM_ARG1, FUNC_NAME);
 275   i_smob = (iterator_smob *) SCM_SMOB_DATA (i_scm);
 276
 277   i_smob->progress = value;
 278   return SCM_UNSPECIFIED;
 279 }
 280
 281 /* (iterator-next! <gdb:iterator>) -> object
 282    The result is the next value in the iteration or some "end" marker.
 283    It is up to each iterator's next! function to specify what its end
 284    marker is.  */
 285
 286 static SCM
 287 gdbscm_iterator_next_x (SCM self)
 288 {
 289   SCM i_scm;
 290   iterator_smob *i_smob;
 291
 292   i_scm = itscm_get_iterator_arg_unsafe (self, SCM_ARG1, FUNC_NAME);
 293   i_smob = (iterator_smob *) SCM_SMOB_DATA (i_scm);
 294   /* We leave type-checking of the procedure to gdbscm_safe_call_1.  */
 295
 296   return gdbscm_safe_call_1 (i_smob->next_x, self, NULL);
 297 }
 298 \f
 299 /* Initialize the Scheme iterator code.  */
 300
 301 static const scheme_function iterator_functions[] =
 302 {
 303   { "make-iterator", 3, 0, 0, as_a_scm_t_subr (gdbscm_make_iterator),
 304     "\
 305 Create a <gdb:iterator> object.\n\
 306 \n\
 307   Arguments: object progress next!\n\
 308     object:   The object to iterate over.\n\
 309     progress: An object to use to track progress of the iteration.\n\
 310     next!:    A procedure of one argument, the iterator.\n\
 311       Returns the next element in the iteration or an implementation-chosen\n\
 312       value to signify iteration is complete.\n\
 313       By convention end-of-iteration should be marked with (end-of-iteration)\n\
 314       from module (gdb iterator)." },
 315
 316   { "iterator?", 1, 0, 0, as_a_scm_t_subr (gdbscm_iterator_p),
 317     "\
 318 Return #t if the object is a <gdb:iterator> object." },
 319
 320   { "iterator-object", 1, 0, 0, as_a_scm_t_subr (gdbscm_iterator_object),
 321     "\
 322 Return the object being iterated over." },
 323
 324   { "iterator-progress", 1, 0, 0, as_a_scm_t_subr (gdbscm_iterator_progress),
 325     "\
 326 Return the progress object of the iterator." },
 327
 328   { "set-iterator-progress!", 2, 0, 0,
 329     as_a_scm_t_subr (gdbscm_set_iterator_progress_x),
 330     "\
 331 Set the progress object of the iterator." },
 332
 333   { "iterator-next!", 1, 0, 0, as_a_scm_t_subr (gdbscm_iterator_next_x),
 334     "\
 335 Invoke the next! procedure of the iterator and return its result." },
 336
 337   { "end-of-iteration", 0, 0, 0, as_a_scm_t_subr (gdbscm_end_of_iteration),
 338     "\
 339 Return the end-of-iteration marker." },
 340
 341   { "end-of-iteration?", 1, 0, 0, as_a_scm_t_subr (gdbscm_end_of_iteration_p),
 342     "\
 343 Return #t if the object is the end-of-iteration marker." },
 344
 345   END_FUNCTIONS
 346 };
 347
 348 void
 349 gdbscm_initialize_iterators (void)
 350 {
 351   iterator_smob_tag = gdbscm_make_smob_type (iterator_smob_name,
 352                                              sizeof (iterator_smob));
 353   scm_set_smob_print (iterator_smob_tag, itscm_print_iterator_smob);
 354
 355   gdbscm_define_functions (iterator_functions, 1);
 356
 357   /* We can make this more unique if it's necessary,
 358      but this is good enough for now.  */
 359   end_of_iteration = scm_from_latin1_keyword ("end-of-iteration");
 360 }