2.9BSD - /usr/src/ucb/pascal/pi/yycosts.c

   1: /*	@(#)yycosts.c	2.3	SCCS id keyword	*/
   2: /* Copyright (c) 1979 Regents of the University of California */
   3: #
   4: /*
   5:  * pi - Pascal interpreter code translator
   6:  *
   7:  * Charles Haley, Bill Joy UCB
   8:  * Version 1.1 February 1978
   9:  *
  10:  *
  11:  * pxp - Pascal execution profiler
  12:  *
  13:  * Bill Joy UCB
  14:  * Version 1.1 February 1978
  15:  */
  16: 
  17: #include "whoami"
  18: #include "0.h"
  19: #include "yy.h"
  20: 
  21: /*
  22:  * Symbol costs for Pascal.
  23:  *
  24:  * Cost strategy of August 14, 1977.
  25:  *
  26:  * The costs determined by the routines in this file are used by
  27:  * the recovery in choosing appropriate corrections.
  28:  * The cost vectors and the error productions in the grammar
  29:  * work together to define the corrective capacity of the grammar.
  30:  *
  31:  * The costs here largely derive from those given in Steve Rhode's
  32:  * thesis for the Pascal-I error correcting parser which he implemented.
  33:  * Some minor changes have been made to adjust for the fact that
  34:  * the current error recovery is not as "smart", both because of the
  35:  * limited forward move and because of the lack of any type information
  36:  * about identifiers.
  37:  *
  38:  * These adjustments largely take the form of increased costs for certain
  39:  * tokens, noticeably keywords which are major brackets such as "begin"
  40:  * "label", "procedure", etc.
  41:  *
  42:  * The overall weighting strategy is still similar to Rhodes' strategy.
  43:  * The costs can be considered:
  44:  *
  45:  *	LOW	<= 3
  46:  *	MEDIUM	4 or 5
  47:  *	HIGH	>= 6
  48:  */
  49: 
  50: /*
  51:  * Insertion costs
  52:  *
  53:  * In addition to the normal symbol insertion costs,
  54:  * there are zero cost insertions here.
  55:  * The current error recovery system treats symbols
  56:  * which have zero insertion cost in a special way,
  57:  * inserting them but suppressing diagnostics.
  58:  * This allows the system to hold of on bracketing
  59:  * error diagnostics about missing end's until the
  60:  * reduction occurs which knows the line number of the
  61:  * corresponding "begin", "repeat", etc.
  62:  * A more intelligent and useful diagnostic can then
  63:  * be printed.
  64:  *
  65:  * Although this routine never allows the insertion
  66:  * of the keyword begin, it can be inserted after a
  67:  * procedure or function body starts, if it was omitted
  68:  * by a special case in the panic routine, which notices
  69:  * the keywords in the statement body of the procedure
  70:  * and inserts the begin to recover.
  71:  *
  72:  * Similarly, we do not insert end-of-file, but
  73:  * the fact that end-of-file is the unique input
  74:  * is noticed by the recovery routines as a special
  75:  * case and handled there.
  76:  */
  77: inscost(sy, before)
  78:     register int sy, before;
  79: {
  80: 
  81:     switch (before) {
  82:         case YEND:
  83:             if (sy == YEND)
  84:                 break;
  85:         case YPROCEDURE:
  86:         case YFUNCTION:
  87:             if (sy == YUNTIL || sy == YEND)
  88:                 return (0);
  89:     }
  90:     switch (sy) {
  91:         case ';':
  92:             return (1);
  93:         case ',':
  94:         case ':':
  95:         case YOF:
  96:         case YDO:
  97:             return (2);
  98:         case YARRAY:
  99:         case '+':
 100:         case '*':
 101:             return (3);
 102:         default:
 103:             return (4);
 104:         case '^':
 105:         case YNOT:
 106:         case YLABEL:
 107:         case YCONST:
 108:         case YTYPE:
 109:         case YVAR:
 110:         case YUNTIL:
 111:         case '(':
 112:         case '[':
 113:         case YWHILE:
 114:         case YWITH:
 115:         case YASSERT:
 116:             return (5);
 117:         case YPROCEDURE:
 118:         case YFUNCTION:
 119:         case YCASE:
 120:             return (6);
 121:         case YEND:
 122:             return (8);
 123:         case YBEGIN:
 124:         case YEOF:
 125:         case YREPEAT:
 126:         case YRECORD:
 127:             return (INFINITY);
 128:     }
 129: }
 130: 
 131: /*
 132:  * Replacement costs
 133:  *
 134:  * Most replacement costs are the same as an insertion
 135:  * plus a deletion cost.  One special case is the replacement
 136:  * of a large number of keywords by an identifier.
 137:  * These are given lower costs, especially the keyword "to".
 138:  */
 139: repcost(what, with)
 140:     register int what, with;
 141: {
 142:     register int c;
 143: 
 144:     if (with == what)
 145:         return (INFINITY);
 146:     if (with == YID && what > ERROR)
 147:         switch (what) {
 148:             case YID:
 149:             case YDOTDOT:
 150:             case YINT:
 151:             case YBINT:
 152:             case YSTRING:
 153:             case YNUMB:
 154:                 break;
 155:             case YTO:
 156:                 return (3);
 157:             default:
 158:                 return (5);
 159:             case YRECORD:
 160:             case YTHEN:
 161:                 return (6);
 162:             case YBEGIN:
 163:                 break;
 164:         }
 165:     if (what == ';' && (with == ',' || with == '.'))
 166:         return (CLIMIT - 1);
 167:     c = delcost(what) + inscost(with);
 168:     /*
 169: 	 * It costs extra to replace something which has
 170: 	 * semantics by something which doesn't.
 171: 	 */
 172:     if (nullsem(what) == NIL && nullsem(with) != NIL)
 173:         c =+ 4;
 174:     return (c);
 175: }
 176: 
 177: /*
 178:  * Deletion costs
 179:  */
 180: delcost(what)
 181:     int what;
 182: {
 183: 
 184:     switch (what) {
 185:         case '.':
 186:         case ':':
 187:         case ',':
 188:         case '=':
 189:         case '(':
 190:             return (3);
 191:         case YELSE:
 192:         case YTHEN:
 193:             return (4);
 194:         default:
 195:             return (5);
 196:         case YLABEL:
 197:         case YCONST:
 198:         case YTYPE:
 199:         case YVAR:
 200:             return (10);
 201:         case YPROCEDURE:
 202:         case YFUNCTION:
 203:         case YBEGIN:
 204:         case YEND:
 205:             return ((CLIMIT * 3) / 4);
 206:         case ';':
 207:         case YEOF:
 208:             return (INFINITY);
 209:     }
 210: }
 211: #ifdef DEBUG
 212: 
 213: /*
 214:  * Routine to print out costs with "-C" option.
 215:  */
 216: char    yysyms[]    ";,:=*+/-|&()[]<>~^";
 217: 
 218: 
 219: yycosts()
 220: {
 221:     register int c;
 222:     register char *cp;
 223: 
 224:     printf("Insert\tDelete\tRep(ID)\tSymbol\n");
 225:     for (cp = yysyms; *cp; cp++)
 226:         yydocost(*cp);
 227:     for (c = ERROR + 1; c < YLAST; c++)
 228:         yydocost(c);
 229: #ifdef PXP
 230:     flush();
 231: #endif
 232: }
 233: 
 234: yydocost(c)
 235:     int c;
 236: {
 237: 
 238:     printf("%4d\t", inscost(c, -1));
 239:     printf("%4d\t", delcost(c));
 240:     if (repcost(c, YID) != inscost(YID) + delcost(c))
 241:         printf("%4d", repcost(c, YID));
 242:     printf("\t%s%s\n", charname(c , 0 ) , charname(c , 1 ));
 243: }
 244: #endif

Defined functions

Defined variables