libguile/read.c

   1 /*      Copyright (C) 1995,1996,1997 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.
  26  *
  27  * This exception does not however invalidate any other reasons why
  28  * the executable file might be covered by the GNU General Public License.
  29  *
  30  * This exception applies only to the code released by the
  31  * Free Software Foundation under the name GUILE.  If you copy
  32  * code from other Free Software Foundation releases into a copy of
  33  * GUILE, as the General Public License permits, the exception does
  34  * not apply to the code that you add in this way.  To avoid misleading
  35  * anyone as to the status of such modified files, you must delete
  36  * this exception notice from them.
  37  *
  38  * If you write modifications of your own for GUILE, it is your choice
  39  * whether to permit this exception to apply to your modifications.
  40  * If you do not wish that, delete this exception notice.  */
  41 \f
  42
  43 #include <stdio.h>
  44 #include "_scm.h"
  45 #include "chars.h"
  46 #include "genio.h"
  47 #include "eval.h"
  48 #include "unif.h"
  49 #include "keywords.h"
  50 #include "alist.h"
  51 #include "srcprop.h"
  52 #include "hashtab.h"
  53 #include "hash.h"
  54
  55 #include "read.h"
  56
  57 \f
  58
  59 SCM_SYMBOL (scm_keyword_prefix, "prefix");
  60
  61 scm_option scm_read_opts[] = {
  62   { SCM_OPTION_BOOLEAN, "copy", 0,
  63     "Copy source code expressions." },
  64   { SCM_OPTION_BOOLEAN, "positions", 0,
  65     "Record positions of source code expressions." },
  66   { SCM_OPTION_BOOLEAN, "case-insensitive", 0,
  67     "Convert symbols to lower case."},
  68   { SCM_OPTION_SCM, "keywords", SCM_BOOL_F,
  69     "Style of keyword recognition: #f or 'prefix"}
  70 };
  71
  72 SCM_PROC (s_read_options, "read-options-interface", 0, 1, 0, scm_read_options);
  73
  74 SCM
  75 scm_read_options (setting)
  76      SCM setting;
  77 {
  78   SCM ans = scm_options (setting,
  79                          scm_read_opts,
  80                          SCM_N_READ_OPTIONS,
  81                          s_read_options);
  82   if (SCM_COPY_SOURCE_P)
  83     SCM_RECORD_POSITIONS_P = 1;
  84   return ans;
  85 }
  86
  87 /* An association list mapping extra hash characters to procedures.  */
  88 static SCM *scm_read_hash_procedures;
  89
  90 SCM_PROC (s_read, "read", 0, 1, 0, scm_read);
  91
  92 SCM
  93 scm_read (port)
  94      SCM port;
  95 {
  96   int c;
  97   SCM tok_buf, copy;
  98
  99   if (SCM_UNBNDP (port))
 100     port = scm_cur_inp;
 101   else
 102     SCM_ASSERT (SCM_NIMP (port) && SCM_OPINPORTP (port),
 103                 port,
 104                 SCM_ARG1,
 105                 s_read);
 106
 107   c = scm_flush_ws (port, (char *) NULL);
 108   if (EOF == c)
 109     return SCM_EOF_VAL;
 110   scm_ungetc (c, port);
 111
 112   tok_buf = scm_makstr (30L, 0);
 113   return scm_lreadr (&tok_buf, port, &copy);
 114 }
 115
 116
 117
 118 char *
 119 scm_grow_tok_buf (tok_buf)
 120      SCM * tok_buf;
 121 {
 122   scm_vector_set_length_x (*tok_buf, SCM_MAKINUM (2 * SCM_LENGTH (*tok_buf)));
 123   return SCM_CHARS (*tok_buf);
 124 }
 125
 126
 127
 128 int
 129 scm_flush_ws (port, eoferr)
 130      SCM port;
 131      const char *eoferr;
 132 {
 133   register int c;
 134   while (1)
 135     switch (c = scm_getc (port))
 136       {
 137       case EOF:
 138       goteof:
 139         if (eoferr)
 140           scm_wta (SCM_UNDEFINED, "end of file in ", eoferr);
 141         return c;
 142       case ';':
 143       lp:
 144         switch (c = scm_getc (port))
 145           {
 146           case EOF:
 147             goto goteof;
 148           default:
 149             goto lp;
 150           case SCM_LINE_INCREMENTORS:
 151             break;
 152           }
 153         break;
 154       case SCM_LINE_INCREMENTORS:
 155       case SCM_SINGLE_SPACES:
 156       case '\t':
 157         break;
 158       default:
 159         return c;
 160       }
 161 }
 162
 163
 164
 165 int
 166 scm_casei_streq (s1, s2)
 167      char * s1;
 168      char * s2;
 169 {
 170   while (*s1 && *s2)
 171     if (scm_downcase((int)*s1) != scm_downcase((int)*s2))
 172       return 0;
 173     else
 174       {
 175         ++s1;
 176         ++s2;
 177       }
 178   return !(*s1 || *s2);
 179 }
 180
 181
 182 /* recsexpr is used when recording expressions
 183  * constructed by read:sharp.
 184  */
 185 #ifndef DEBUG_EXTENSIONS
 186 #define recsexpr(obj, line, column, filename) (obj)
 187 #else
 188 static SCM recsexpr SCM_P ((SCM obj, int line, int column, SCM filename));
 189
 190 static SCM
 191 recsexpr (obj, line, column, filename)
 192      SCM obj;
 193      int line;
 194      int column;
 195      SCM filename;
 196 {
 197   if (SCM_IMP (obj) || SCM_NCONSP(obj))
 198     return obj;
 199   {
 200     SCM tmp = obj, copy;
 201     /* If this sexpr is visible in the read:sharp source, we want to
 202        keep that information, so only record non-constant cons cells
 203        which haven't previously been read by the reader. */
 204     if (SCM_FALSEP (scm_whash_lookup (scm_source_whash, obj)))
 205       {
 206         if (SCM_COPY_SOURCE_P)
 207           {
 208             copy = scm_cons (recsexpr (SCM_CAR (obj), line, column, filename),
 209                              SCM_UNDEFINED);
 210             while (SCM_NIMP (tmp = SCM_CDR (tmp)) && SCM_CONSP (tmp))
 211               {
 212                 SCM_SETCDR (copy, scm_cons (recsexpr (SCM_CAR (tmp),
 213                                                       line,
 214                                                       column,
 215                                                       filename),
 216                                             SCM_UNDEFINED));
 217                 copy = SCM_CDR (copy);
 218               }
 219             SCM_SETCDR (copy, tmp);
 220           }
 221         else
 222           {
 223             recsexpr (SCM_CAR (obj), line, column, filename);
 224             while (SCM_NIMP (tmp = SCM_CDR (tmp)) && SCM_CONSP (tmp))
 225               recsexpr (SCM_CAR (tmp), line, column, filename);
 226             copy = SCM_UNDEFINED;
 227           }
 228         scm_whash_insert (scm_source_whash,
 229                           obj,
 230                           scm_make_srcprops (line,
 231                                              column,
 232                                              filename,
 233                                              copy,
 234                                              SCM_EOL));
 235       }
 236     return obj;
 237   }
 238 }
 239 #endif
 240
 241 /* Consume an SCSH-style block comment.  Assume that we've already
 242    read the initial `#!', and eat characters until we get a
 243    newline/exclamation-point/sharp-sign/newline sequence.  */
 244
 245 static void
 246 skip_scsh_block_comment (port)
 247      SCM port;
 248 {
 249   /* Is this portable?  Dear God, spare me from the non-eight-bit
 250      characters.  But is it tasteful?  */
 251   long history = 0;
 252
 253   for (;;)
 254     {
 255       int c = scm_getc (port);
 256
 257       if (c == EOF)
 258         scm_wta (SCM_UNDEFINED,
 259                  "unterminated `#! ... !#' comment", "read");
 260       history = ((history << 8) | (c & 0xff)) & 0xffffffff;
 261
 262       /* Were the last four characters read "\n!#\n"?  */
 263       if (history == (('\n' << 24) | ('!' << 16) | ('#' << 8) | '\n'))
 264         return;
 265     }
 266 }
 267
 268 static SCM
 269 scm_get_hash_procedure SCM_P ((int c));
 270
 271 static char s_list[]="list";
 272
 273 SCM
 274 scm_lreadr (tok_buf, port, copy)
 275      SCM *tok_buf;
 276      SCM port;
 277      SCM *copy;
 278 {
 279   int c;
 280   scm_sizet j;
 281   SCM p;
 282
 283 tryagain:
 284   c = scm_flush_ws (port, s_read);
 285 tryagain_no_flush_ws:
 286   switch (c)
 287     {
 288     case EOF:
 289       return SCM_EOF_VAL;
 290
 291     case '(':
 292       return SCM_RECORD_POSITIONS_P
 293              ? scm_lreadrecparen (tok_buf, port, s_list, copy)
 294              : scm_lreadparen (tok_buf, port, s_list, copy);
 295     case ')':
 296       scm_wta (SCM_UNDEFINED, "unexpected \")\"", "read");
 297       goto tryagain;
 298
 299     case '\'':
 300       p = scm_i_quote;
 301       goto recquote;
 302     case '`':
 303       p = scm_i_quasiquote;
 304       goto recquote;
 305     case ',':
 306       c = scm_getc (port);
 307       if ('@' == c)
 308         p = scm_i_uq_splicing;
 309       else
 310         {
 311           scm_ungetc (c, port);
 312           p = scm_i_unquote;
 313         }
 314     recquote:
 315       p = scm_cons2 (p,
 316                      scm_lreadr (tok_buf, port, copy),
 317                      SCM_EOL);
 318       if (SCM_RECORD_POSITIONS_P)
 319         scm_whash_insert (scm_source_whash,
 320                           p,
 321                           scm_make_srcprops (SCM_LINUM (port),
 322                                              SCM_COL (port) - 1,
 323                                              SCM_FILENAME (port),
 324                                              SCM_COPY_SOURCE_P
 325                                              ? (*copy = scm_cons2 (SCM_CAR (p),
 326                                                                    SCM_CAR (SCM_CDR (p)),
 327                                                                    SCM_EOL))
 328                                              : SCM_UNDEFINED,
 329                                              SCM_EOL));
 330       return p;
 331     case '#':
 332       c = scm_getc (port);
 333       switch (c)
 334         {
 335         case '(':
 336           p = scm_lreadparen (tok_buf, port, "vector", copy);
 337           return SCM_NULLP (p) ? scm_nullvect : scm_vector (p);
 338
 339         case 't':
 340         case 'T':
 341           return SCM_BOOL_T;
 342         case 'f':
 343         case 'F':
 344           return SCM_BOOL_F;
 345
 346         case 'b':
 347         case 'B':
 348         case 'o':
 349         case 'O':
 350         case 'd':
 351         case 'D':
 352         case 'x':
 353         case 'X':
 354         case 'i':
 355         case 'I':
 356         case 'e':
 357         case 'E':
 358           scm_ungetc (c, port);
 359           c = '#';
 360           goto num;
 361
 362         case '!':
 363           /* start of a shell script.  Parse as a block comment,
 364              terminated by !#, just like SCSH.  */
 365           skip_scsh_block_comment (port);
 366           /* EOF is not an error here */
 367           c = scm_flush_ws (port, (char *)NULL);
 368           goto tryagain_no_flush_ws;
 369
 370         case '*':
 371           j = scm_read_token (c, tok_buf, port, 0);
 372           p = scm_istr2bve (SCM_CHARS (*tok_buf) + 1, (long) (j - 1));
 373           if (SCM_NFALSEP (p))
 374             return p;
 375           else
 376             goto unkshrp;
 377
 378         case '{':
 379           j = scm_read_token (c, tok_buf, port, 1);
 380           p = scm_intern (SCM_CHARS (*tok_buf), j);
 381           return SCM_CAR (p);
 382
 383         case '\\':
 384           c = scm_getc (port);
 385           j = scm_read_token (c, tok_buf, port, 0);
 386           if (j == 1)
 387             return SCM_MAKICHR (c);
 388           if (c >= '0' && c < '8')
 389             {
 390               p = scm_istr2int (SCM_CHARS (*tok_buf), (long) j, 8);
 391               if (SCM_NFALSEP (p))
 392                 return SCM_MAKICHR (SCM_INUM (p));
 393             }
 394           for (c = 0; c < scm_n_charnames; c++)
 395             if (scm_charnames[c]
 396                 && (scm_casei_streq (scm_charnames[c], SCM_CHARS (*tok_buf))))
 397               return SCM_MAKICHR (scm_charnums[c]);
 398           scm_wta (SCM_UNDEFINED, "unknown # object: #\\", SCM_CHARS (*tok_buf));
 399
 400           /* #:SYMBOL is a syntax for keywords supported in all contexts.  */
 401         case ':':
 402           j = scm_read_token ('-', tok_buf, port, 0);
 403           p = scm_intern (SCM_CHARS (*tok_buf), j);
 404           return scm_make_keyword_from_dash_symbol (SCM_CAR (p));
 405
 406         default:
 407         callshrp:
 408           {
 409             SCM sharp = scm_get_hash_procedure (c);
 410
 411             if (SCM_NIMP (sharp))
 412               {
 413                 int line = SCM_LINUM (port);
 414                 int column = SCM_COL (port) - 2;
 415                 SCM got;
 416
 417                 got = scm_apply (sharp,
 418                                  SCM_MAKICHR (c),
 419                                  scm_acons (port, SCM_EOL, SCM_EOL));
 420                 if (SCM_UNSPECIFIED == got)
 421                   goto unkshrp;
 422                 if (SCM_RECORD_POSITIONS_P)
 423                   return *copy = recsexpr (got, line, column,
 424                                            SCM_FILENAME (port));
 425                 else
 426                   return got;
 427               }
 428           }
 429         unkshrp:
 430           scm_misc_error (s_read, "Unknown # object: %S",
 431                           scm_listify (SCM_MAKICHR (c), SCM_UNDEFINED));
 432         }
 433
 434     case '"':
 435       j = 0;
 436       while ('"' != (c = scm_getc (port)))
 437         {
 438           SCM_ASSERT (EOF != c, SCM_UNDEFINED, "end of file in ", "string");
 439
 440           while (j + 2 >= SCM_LENGTH (*tok_buf))
 441             scm_grow_tok_buf (tok_buf);
 442
 443           if (c == '\\')
 444             switch (c = scm_getc (port))
 445               {
 446               case '\n':
 447                 continue;
 448               case '0':
 449                 c = '\0';
 450                 break;
 451               case 'f':
 452                 c = '\f';
 453                 break;
 454               case 'n':
 455                 c = '\n';
 456                 break;
 457               case 'r':
 458                 c = '\r';
 459                 break;
 460               case 't':
 461                 c = '\t';
 462                 break;
 463               case 'a':
 464                 c = '\007';
 465                 break;
 466               case 'v':
 467                 c = '\v';
 468                 break;
 469               }
 470           SCM_CHARS (*tok_buf)[j] = c;
 471           ++j;
 472         }
 473       if (j == 0)
 474         return scm_nullstr;
 475       SCM_CHARS (*tok_buf)[j] = 0;
 476       {
 477         SCM str;
 478         str = scm_makfromstr (SCM_CHARS (*tok_buf), j, 0);
 479         return str;
 480       }
 481
 482     case'0':case '1':case '2':case '3':case '4':
 483     case '5':case '6':case '7':case '8':case '9':
 484     case '.':
 485     case '-':
 486     case '+':
 487     num:
 488       j = scm_read_token (c, tok_buf, port, 0);
 489       p = scm_istring2number (SCM_CHARS (*tok_buf), (long) j, 10L);
 490       if (SCM_NFALSEP (p))
 491         return p;
 492       if (c == '#')
 493         {
 494           if ((j == 2) && (scm_getc (port) == '('))
 495             {
 496               scm_ungetc ('(', port);
 497               c = SCM_CHARS (*tok_buf)[1];
 498               goto callshrp;
 499             }
 500           scm_wta (SCM_UNDEFINED, "unknown # object", SCM_CHARS (*tok_buf));
 501         }
 502       goto tok;
 503
 504     case ':':
 505       if (SCM_KEYWORD_STYLE == scm_keyword_prefix)
 506         {
 507           j = scm_read_token ('-', tok_buf, port, 0);
 508           p = scm_intern (SCM_CHARS (*tok_buf), j);
 509           return scm_make_keyword_from_dash_symbol (SCM_CAR (p));
 510         }
 511       /* fallthrough */
 512     default:
 513       j = scm_read_token (c, tok_buf, port, 0);
 514       /* fallthrough */
 515
 516     tok:
 517       p = scm_intern (SCM_CHARS (*tok_buf), j);
 518       return SCM_CAR (p);
 519     }
 520 }
 521
 522 #ifdef _UNICOS
 523 _Pragma ("noopt");              /* # pragma _CRI noopt */
 524 #endif
 525
 526 scm_sizet
 527 scm_read_token (ic, tok_buf, port, weird)
 528      int ic;
 529      SCM *tok_buf;
 530      SCM port;
 531      int weird;
 532 {
 533   register scm_sizet j;
 534   register int c;
 535   register char *p;
 536
 537   c = (SCM_CASE_INSENSITIVE_P ? scm_downcase(ic) : ic);
 538   p = SCM_CHARS (*tok_buf);
 539
 540   if (weird)
 541     j = 0;
 542   else
 543     {
 544       j = 0;
 545       while (j + 2 >= SCM_LENGTH (*tok_buf))
 546         p = scm_grow_tok_buf (tok_buf);
 547       p[j] = c;
 548       ++j;
 549     }
 550
 551   while (1)
 552     {
 553       while (j + 2 >= SCM_LENGTH (*tok_buf))
 554         p = scm_grow_tok_buf (tok_buf);
 555       c = scm_getc (port);
 556       switch (c)
 557         {
 558         case '(':
 559         case ')':
 560         case '"':
 561         case ';':
 562         case SCM_WHITE_SPACES:
 563         case SCM_LINE_INCREMENTORS:
 564           if (weird)
 565             goto default_case;
 566
 567           scm_ungetc (c, port);
 568         case EOF:
 569         eof_case:
 570           p[j] = 0;
 571           return j;
 572         case '\\':
 573           if (!weird)
 574             goto default_case;
 575           else
 576             {
 577               c = scm_getc (port);
 578               if (c == EOF)
 579                 goto eof_case;
 580               else
 581                 goto default_case;
 582             }
 583         case '}':
 584           if (!weird)
 585             goto default_case;
 586
 587           c = scm_getc (port);
 588           if (c == '#')
 589             {
 590               p[j] = 0;
 591               return j;
 592             }
 593           else
 594             {
 595               scm_ungetc (c, port);
 596               c = '}';
 597               goto default_case;
 598             }
 599
 600         default:
 601         default_case:
 602           {
 603             c = (SCM_CASE_INSENSITIVE_P ? scm_downcase(c) : c);
 604             p[j] = c;
 605             ++j;
 606           }
 607
 608         }
 609     }
 610 }
 611
 612 #ifdef _UNICOS
 613 _Pragma ("opt");                /* # pragma _CRI opt */
 614 #endif
 615
 616 SCM
 617 scm_lreadparen (tok_buf, port, name, copy)
 618      SCM *tok_buf;
 619      SCM port;
 620      char *name;
 621      SCM *copy;
 622 {
 623   SCM tmp;
 624   SCM tl;
 625   SCM ans;
 626   int c;
 627
 628   c = scm_flush_ws (port, name);
 629   if (')' == c)
 630     return SCM_EOL;
 631   scm_ungetc (c, port);
 632   if (scm_i_dot == (tmp = scm_lreadr (tok_buf, port, copy)))
 633     {
 634       ans = scm_lreadr (tok_buf, port, copy);
 635     closeit:
 636       if (')' != (c = scm_flush_ws (port, name)))
 637         scm_wta (SCM_UNDEFINED, "missing close paren", "");
 638       return ans;
 639     }
 640   ans = tl = scm_cons (tmp, SCM_EOL);
 641   while (')' != (c = scm_flush_ws (port, name)))
 642     {
 643       scm_ungetc (c, port);
 644       if (scm_i_dot == (tmp = scm_lreadr (tok_buf, port, copy)))
 645         {
 646           SCM_SETCDR (tl, scm_lreadr (tok_buf, port, copy));
 647           goto closeit;
 648         }
 649       SCM_SETCDR (tl, scm_cons (tmp, SCM_EOL));
 650       tl = SCM_CDR (tl);
 651     }
 652   return ans;
 653 }
 654
 655
 656 SCM
 657 scm_lreadrecparen (tok_buf, port, name, copy)
 658      SCM *tok_buf;
 659      SCM port;
 660      char *name;
 661      SCM *copy;
 662 {
 663   register int c;
 664   register SCM tmp;
 665   register SCM tl, tl2 = SCM_EOL;
 666   SCM ans, ans2 = SCM_EOL;
 667   /* Need to capture line and column numbers here. */
 668   int line = SCM_LINUM (port);
 669   int column = SCM_COL (port) - 1;
 670
 671   c = scm_flush_ws (port, name);
 672   if (')' == c)
 673     return SCM_EOL;
 674   scm_ungetc (c, port);
 675   if (scm_i_dot == (tmp = scm_lreadr (tok_buf, port, copy)))
 676     {
 677       ans = scm_lreadr (tok_buf, port, copy);
 678       if (')' != (c = scm_flush_ws (port, name)))
 679         scm_wta (SCM_UNDEFINED, "missing close paren", "");
 680       return ans;
 681     }
 682   /* Build the head of the list structure. */
 683   ans = tl = scm_cons (tmp, SCM_EOL);
 684   if (SCM_COPY_SOURCE_P)
 685     ans2 = tl2 = scm_cons (SCM_NIMP (tmp) && SCM_CONSP (tmp)
 686                            ? *copy
 687                            : tmp,
 688                            SCM_EOL);
 689   while (')' != (c = scm_flush_ws (port, name)))
 690     {
 691       scm_ungetc (c, port);
 692       if (scm_i_dot == (tmp = scm_lreadr (tok_buf, port, copy)))
 693         {
 694           SCM_SETCDR (tl, tmp = scm_lreadr (tok_buf, port, copy));
 695           if (SCM_COPY_SOURCE_P)
 696             SCM_SETCDR (tl2, scm_cons (SCM_NIMP (tmp) && SCM_CONSP (tmp)
 697                                        ? *copy
 698                                        : tmp,
 699                                        SCM_EOL));
 700           if (')' != (c = scm_flush_ws (port, name)))
 701             scm_wta (SCM_UNDEFINED, "missing close paren", "");
 702           goto exit;
 703         }
 704       tl = SCM_SETCDR (tl, scm_cons (tmp, SCM_EOL));
 705       if (SCM_COPY_SOURCE_P)
 706         tl2 = SCM_SETCDR (tl2, scm_cons (SCM_NIMP (tmp) && SCM_CONSP (tmp)
 707                                          ? *copy
 708                                          : tmp,
 709                                          SCM_EOL));
 710     }
 711 exit:
 712   scm_whash_insert (scm_source_whash,
 713                     ans,
 714                     scm_make_srcprops (line,
 715                                        column,
 716                                        SCM_FILENAME (port),
 717                                        SCM_COPY_SOURCE_P
 718                                        ? *copy = ans2
 719                                        : SCM_UNDEFINED,
 720                                        SCM_EOL));
 721   return ans;
 722 }
 723
 724
 725 \f
 726
 727 /* Manipulate the read-hash-procedures alist.  This could be written in
 728    Scheme, but maybe it will also be used by C code during initialisation.  */
 729 SCM_PROC (s_read_hash_extend, "read-hash-extend", 2, 0, 0, scm_read_hash_extend);
 730 SCM
 731 scm_read_hash_extend (chr, proc)
 732      SCM chr;
 733      SCM proc;
 734 {
 735   SCM this;
 736   SCM prev;
 737
 738   SCM_ASSERT (SCM_ICHRP(chr), chr, SCM_ARG1, s_read_hash_extend);
 739   SCM_ASSERT (SCM_FALSEP (proc) || SCM_NIMP(proc), proc, SCM_ARG2,
 740               s_read_hash_extend);
 741
 742   /* Check if chr is already in the alist.  */
 743   this = *scm_read_hash_procedures;
 744   prev = SCM_BOOL_F;
 745   while (1)
 746     {
 747       if (SCM_NULLP (this))
 748         {
 749           /* not found, so add it to the beginning.  */
 750           if (SCM_NFALSEP (proc))
 751             {
 752               *scm_read_hash_procedures =
 753                 scm_cons (scm_cons (chr, proc), *scm_read_hash_procedures);
 754             }
 755           break;
 756         }
 757       if (chr == SCM_CAAR (this))
 758         {
 759           /* already in the alist.  */
 760           if (SCM_FALSEP (proc))
 761             {
 762               /* remove it.  */
 763               if (prev == SCM_BOOL_F)
 764                 {
 765                   *scm_read_hash_procedures =
 766                     SCM_CDR (*scm_read_hash_procedures);
 767                 }
 768               else
 769                 scm_set_cdr_x (prev, SCM_CDR (this));
 770             }
 771           else
 772             {
 773               /* replace it.  */
 774               scm_set_cdr_x (SCM_CAR (this), proc);
 775             }
 776           break;
 777         }
 778       prev = this;
 779       this = SCM_CDR (this);
 780     }
 781
 782   return SCM_UNSPECIFIED;
 783 }
 784
 785 /* Recover the read-hash procedure corresponding to char c.  */
 786 static SCM
 787 scm_get_hash_procedure (c)
 788      int c;
 789 {
 790   SCM rest = *scm_read_hash_procedures;
 791
 792   while (1)
 793     {
 794       if (SCM_NULLP (rest))
 795         return SCM_BOOL_F;
 796
 797       if (SCM_ICHR (SCM_CAAR (rest)) == c)
 798         return SCM_CDAR (rest);
 799
 800       rest = SCM_CDR (rest);
 801     }
 802 }
 803
 804 void
 805 scm_init_read ()
 806 {
 807   scm_read_hash_procedures =
 808     SCM_CDRLOC (scm_sysintern ("read-hash-procedures", SCM_EOL));
 809
 810   scm_init_opts (scm_read_options, scm_read_opts, SCM_N_READ_OPTIONS);
 811 #include "read.x"
 812 }