libguile/read.c

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