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

   1: #
   2: /*
   3:  * pi - Pascal interpreter code translator
   4:  *
   5:  * Charles Haley, Bill Joy UCB
   6:  * Version 1.2 January 1979
   7:  *
   8:  *
   9:  * pxp - Pascal execution profiler
  10:  *
  11:  * Bill Joy UCB
  12:  * Version 1.2 January 1979
  13:  */
  14: 
  15: #include "0.h"
  16: #include "yy.h"
  17: 
  18: /*
  19:  * Symbol costs for Pascal.
  20:  *
  21:  * Cost strategy of August 14, 1977.
  22:  *
  23:  * The costs determined by the routines in this file are used by
  24:  * the recovery in choosing appropriate corrections.
  25:  * The cost vectors and the error productions in the grammar
  26:  * work together to define the corrective capacity of the grammar.
  27:  *
  28:  * The costs here largely derive from those given in Steve Rhode's
  29:  * thesis for the Pascal-I error correcting parser which he implemented.
  30:  * Some minor changes have been made to adjust for the fact that
  31:  * the current error recovery is not as "smart", both because of the
  32:  * limited forward move and because of the lack of any type information
  33:  * about identifiers.
  34:  *
  35:  * These adjustments largely take the form of increased costs for certain
  36:  * tokens, noticeably keywords which are major brackets such as "begin"
  37:  * "label", "procedure", etc.
  38:  *
  39:  * The overall weighting strategy is still similar to Rhodes' strategy.
  40:  * The costs can be considered:
  41:  *
  42:  *	LOW	<= 3
  43:  *	MEDIUM	4 or 5
  44:  *	HIGH	>= 6
  45:  */
  46: 
  47: /*
  48:  * Insertion costs
  49:  *
  50:  * In addition to the normal symbol insertion costs,
  51:  * there are zero cost insertions here.
  52:  * The current error recovery system treats symbols
  53:  * which have zero insertion cost in a special way,
  54:  * inserting them but suppressing diagnostics.
  55:  * This allows the system to hold of on bracketing
  56:  * error diagnostics about missing end's until the
  57:  * reduction occurs which knows the line number of the
  58:  * corresponding "begin", "repeat", etc.
  59:  * A more intelligent and useful diagnostic can then
  60:  * be printed.
  61:  *
  62:  * Although this routine never allows the insertion
  63:  * of the keyword begin, it can be inserted after a
  64:  * procedure or function body starts, if it was omitted
  65:  * by a special case in the panic routine, which notices
  66:  * the keywords in the statement body of the procedure
  67:  * and inserts the begin to recover.
  68:  *
  69:  * Similarly, we do not insert end-of-file, but
  70:  * the fact that end-of-file is the unique input
  71:  * is noticed by the recovery routines as a special
  72:  * case and handled there.
  73:  */
  74: inscost(sy, before)
  75:     register int sy, before;
  76: {
  77: 
  78:     switch (before) {
  79:         case YEND:
  80:             if (sy == YEND)
  81:                 break;
  82:         case YPROCEDURE:
  83:         case YFUNCTION:
  84:             if (sy == YUNTIL || sy == YEND)
  85:                 return (0);
  86:     }
  87:     switch (sy) {
  88:         case ';':
  89:             return (1);
  90:         case ',':
  91:         case ':':
  92:         case YOF:
  93:         case YDO:
  94:         case '.':
  95:             return (2);
  96:         case YARRAY:
  97:         case '+':
  98:         case '*':
  99:             return (3);
 100:         default:
 101:             return (4);
 102:         case '^':
 103:         case YNOT:
 104:         case YLABEL:
 105:         case YCONST:
 106:         case YTYPE:
 107:         case YVAR:
 108:         case YUNTIL:
 109:         case '(':
 110:         case '[':
 111:         case YWHILE:
 112:         case YWITH:
 113:         case YASSERT:
 114:             return (5);
 115:         case YPROCEDURE:
 116:         case YFUNCTION:
 117:         case YCASE:
 118:             return (6);
 119:         case YEND:
 120:             return (8);
 121:         case YBEGIN:
 122:         case YEOF:
 123:         case YREPEAT:
 124:         case YRECORD:
 125:             return (INFINITY);
 126:     }
 127: }
 128: 
 129: /*
 130:  * Replacement costs
 131:  *
 132:  * Most replacement costs are the same as an insertion
 133:  * plus a deletion cost.  One special case is the replacement
 134:  * of a large number of keywords by an identifier.
 135:  * These are given lower costs, especially the keyword "to".
 136:  */
 137: repcost(what, with)
 138:     register int what, with;
 139: {
 140:     register int c;
 141: 
 142:     if (with == what)
 143:         return (INFINITY);
 144:     if (with == YID && what > ERROR)
 145:         switch (what) {
 146:             case YID:
 147:             case YDOTDOT:
 148:             case YINT:
 149:             case YBINT:
 150:             case YSTRING:
 151:             case YNUMB:
 152:                 break;
 153:             case YTO:
 154:                 return (3);
 155:             default:
 156:                 return (5);
 157:             case YRECORD:
 158:             case YTHEN:
 159:                 return (6);
 160:             case YBEGIN:
 161:                 break;
 162:         }
 163:     if (what == ';' && (with == ',' || with == '.'))
 164:         return (CLIMIT - 1);
 165:     c = delcost(what) + inscost(with);
 166:     /*
 167: 	 * It costs extra to replace something which has
 168: 	 * semantics by something which doesn't.
 169: 	 */
 170:     if (nullsem(what) == NIL && nullsem(with) != NIL)
 171:         c =+ 4;
 172:     return (c);
 173: }
 174: 
 175: /*
 176:  * Deletion costs
 177:  */
 178: delcost(what)
 179:     int what;
 180: {
 181: 
 182:     switch (what) {
 183:         case '.':
 184:         case ':':
 185:         case ',':
 186:         case '=':
 187:         case '(':
 188:             return (3);
 189:         case YELSE:
 190:         case YTHEN:
 191:             return (4);
 192:         default:
 193:             return (5);
 194:         case YLABEL:
 195:         case YCONST:
 196:         case YTYPE:
 197:         case YVAR:
 198:             return (10);
 199:         case YPROCEDURE:
 200:         case YFUNCTION:
 201:         case YBEGIN:
 202:         case YEND:
 203:             return ((CLIMIT * 3) / 4);
 204:         case ';':
 205:         case YEOF:
 206:             return (INFINITY);
 207:     }
 208: }
 209: #ifdef DEBUG
 210: 
 211: /*
 212:  * Routine to print out costs with "-C" option.
 213:  */
 214: char    yysyms[]    ".;,:=*+/-|&()[]<>~^";
 215: 
 216: 
 217: yycosts()
 218: {
 219:     register int c;
 220:     register char *cp;
 221: 
 222:     printf("Insert\tDelete\tRep(ID)\tSymbol\n");
 223:     for (cp = yysyms; *cp; cp++)
 224:         yydocost(*cp);
 225:     for (c = ERROR + 1; c < YLAST; c++)
 226:         yydocost(c);
 227: #ifdef PXP
 228:     flush();
 229: #endif
 230: }
 231: 
 232: yydocost(c)
 233:     int c;
 234: {
 235: 
 236:     printf("%4d\t", inscost(c, -1));
 237:     printf("%4d\t", delcost(c));
 238:     if (repcost(c, YID) != inscost(YID) + delcost(c))
 239:         printf("%4d", repcost(c, YID));
 240:     printf("\t%s%s\n", charname(c));
 241: }
 242: #endif

Defined functions

Defined variables