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